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Nervous system ‫الجهاز‬ ‫العصبي‬ •The nervous system can be divided into two main anatomical parts: the central nervous system (CNS) and the peripheral nervous system (PNS) ‫مرکزی‬ ‫عصبی‬ ‫سیستم‬ :‫میشود‬ ‫تقسیم‬ ‫اصلی‬ ‫بخش‬ ‫دو‬ ‫به‬ ‫آناتومیکی‬ ‫نظر‬ ‫از‬ ‫عصبی‬ ‫سیستم‬ ) CNS ) ‫سیستم‬ ‫و‬ ‫محیطی‬ ‫عصبی‬ )PNS) •The central nervous system consists of the brain and spinal cord. ‫یشمل‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫الدماغ‬ ‫والنخاع‬ ‫الشوكي‬ . •It (CNS) receives and processes information from the organs and then sends information back to the organs, instructing them to perform various tasks . ‫یتلقى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫المعلومات‬ ‫من‬ ‫األعضاء‬ ‫ویعالجها‬ ‫ثم‬ ‫یعید‬ ‫المعلومات‬ ‫المعالجة‬ ‫إلى‬ ‫األعضاء‬ ‫ویأمر‬ ‫باإلجراءات‬ ‫التي‬ ‫یتعین‬ ‫القیام‬ ‫بها‬ . ‫یعطي‬ ‫األطراف‬ ‫أجزاء‬ ‫مختلفة‬ . •The central nervous system is also the site of learning ,memory, emotions, and other complex functions. ‫یعد‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫ًا‬‫ض‬‫أی‬ ‫المكان‬ ‫المناسب‬ ‫للقیام‬ ‫بأشیاء‬ ‫مثل‬ ‫التعلم‬ ‫والذاكرة‬ ‫والعواطف‬ ‫والوظائف‬ ‫المعقدة‬ ‫األخرى‬ . •The peripheral nervous system consists of nerve cells that provide communication between the central nervous system and organs throughout the body . ‫یتكون‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫التي‬ ‫تربط‬ ‫بین‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫واألعضاء‬ ‫المختلفة‬ ‫في‬ ‫جمیع‬ ‫أنحاء‬ ‫الجسم‬ . •The peripheral nervous system can be subdivided into two divisions: •Afferent •Efferent ‫یمكن‬ ‫تقسیم‬ PNS ‫إلى‬ ‫قسمین‬ : ‫أفاران‬. ‫وابران‬
•Nerve cells of the afferent division transmit information from the organs to the central nervous system. ‫تحمل‬ ‫الخالیا‬ ‫العصبیة‬ ‫األفارانیة‬ ‫المعلومات‬ ‫من‬ ‫األعضاء‬ ‫إلى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ . •Information transmitted to the central nervous system includes sensory information pertaining to the external environment (such as touch, temperature, vision, and sound) and visceral information pertaining to the internal environment (such as fullness of the stomach, blood pressure, and blood pH) ‫تتضمن‬ ‫المعلومات‬ ‫المرسلة‬ ‫إلى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫المعلومات‬ ‫الحسیة‬ ‫الواردة‬ ‫من‬ ‫البیئة‬ ‫الخارجیة‬ ( ‫مثل‬ ‫اللمس‬ ‫ودرجة‬ ‫الحرارة‬ ‫والبصر‬ ‫والصوت‬ ) ‫باإلضافة‬ ‫إلى‬ ‫المعلومات‬ ‫العمیقة‬ ‫الواردة‬ ‫من‬ ‫البیئة‬ . ‫داخل‬ ‫الجسم‬ ( ‫مثل‬ ‫امتالء‬ ‫المعدة‬ ‫وضغط‬ ‫الدم‬ ‫ودرجة‬ ‫حموضة‬ ‫الدم‬ ) . •Nerve cells of the efferent division transmit information from the central nervous system to organs in the periphery, called effector organs that perform functions in response to commands from neurons. ‫تنقل‬ ‫الخالیا‬ ‫العصبیة‬ ‫الصادرة‬ ‫المعلومات‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫إ‬ ‫لى‬ ‫األعضاء‬ . ‫تسمى‬ ‫هذه‬ ‫األعضاء‬ ‫باألعضاء‬ ‫الوظیفیة‬ ، ‫وهي‬ ‫في‬ ‫الواقع‬ ‫أوامر‬ ‫إنهم‬ ‫یفعلون‬ . •Effector organs are usually muscles and glands. ‫عادة‬ ‫ما‬ ‫تكون‬ ‫األعضاء‬ ‫النشطة‬ ‫عبارة‬ ‫عن‬ ‫عضالت‬ ‫وغدد‬ . •A neuron capable of transmitting messages to an effector organ is said to innervate that effector organ. ‫إن‬ ‫العصب‬ ‫الذي‬ ‫لدیه‬ ‫القدرة‬ ‫على‬ ‫نقل‬ ‫رسالة‬ ‫إلى‬ ‫عضو‬ ‫نشط‬ ‫هو‬ ‫في‬ ‫الواقع‬ ‫یعصب‬ ‫األعضاء‬ ‫النشطة‬ .
•The efferent division can be further subdivided into two main branches: •Somatic nervous system (SNS) •Autonornic nervous system (ANS) ‫ینقسم‬ ‫الجزء‬ ‫الصادر‬ ‫إلى‬ ‫جزأین‬ ‫رئیسیین‬ : ‫الجهاز‬ ‫العصبي‬ ‫للجسم‬ (SNS) ، ‫والجهاز‬ ‫العصبي‬ ‫الالإرادي‬ (ANS) •The somatic nervous system consists of the nerve cells (called motor neurons) that regulate skeletal muscle contractions. ‫تحتوي‬ SNS ‫على‬ ‫خالیا‬ ‫عصبیة‬ ‫تتحكم‬ ‫في‬ ‫تقلصات‬ ‫العضالت‬ ‫الهیكلیة‬ ( ‫الخالیا‬ ‫العصبیة‬ ‫الحركیة‬ ) •The autonomic nervous system consists of nerve cells that regulate the function of internal organs and other structures (such as sweat glands and blood vessels) that are not under voluntary control. ‫یتكون‬ S ( ‫الجهاز‬ ‫العصبي‬ ‫الالإرادي‬ ) ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫التي‬ ‫تتحكم‬ ‫في‬ ‫األعضاء‬ ‫الداخلیة‬ ‫والبنى‬ ‫الداخلیة‬ ‫األخرى‬ ‫التي‬ ‫تفتقر‬ ‫هي‬ ‫الضوابط‬ ‫الطوعیة‬ ( ‫مثل‬ ‫الغدد‬ ‫العرقیة‬ ‫واألوعیة‬ ‫الدمویة‬ ) . •The autonomic nervous system can be divided into two branches: •Parasympathetic nervous systems •Sympathetic nervous systems
‫ینقسم‬ ‫الجهاز‬ ‫العصبي‬ ‫السمبثاوي‬ ‫نفسه‬ ‫إلى‬ ‫فرعین‬ ‫رئیسیین‬ : ‫الجهاز‬ ‫العصبي‬ ‫السمبثاوي‬ ‫والجهاز‬ ‫العصبي‬ ‫الودي‬ •These two branches tend to have opoosite effects on organs. ‫عادة‬ ‫ما‬ ‫یكون‬ ‫لهذین‬ ‫الجهازین‬ ‫العصبیین‬ ‫تأثیرات‬ ‫معاكس‬ ‫ة‬ . •The body also has an enteric nervous system (ENS), which consists of an intricate network of nerve cells in the gastrointestinal tract that can function independently of the rest of the nervous system but communicates with the autonomic nervous system. ‫یحتوي‬ ‫الجسم‬ ‫ًا‬‫ض‬‫أی‬ ‫على‬ ‫جهاز‬ ‫عصبي‬ ‫آخر‬ ‫یسمى‬ ‫الجهاز‬ ‫العصبي‬ ‫المعوي‬ (ENS) ، ‫وهو‬ ‫عبارة‬ ‫عن‬ ‫شبكة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجهاز‬ ‫الهضمي‬ . ‫یمكن‬ ‫أن‬ ‫یعمل‬ ‫بشكل‬ ‫مستقل‬ ‫عن‬ ‫أجزاء‬ ‫أخرى‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ، ‫ولكن‬ ‫لدیه‬ ‫ًا‬‫ض‬‫أی‬ ‫اتصاالت‬ ‫بالجهاز‬ ‫العصبي‬ ANS Cells of the Nervous System ‫خالیا‬ ‫الجهاز‬ ‫العصبي‬ •The nervous system contains two main classes of cells : •Neurons •Glial cells ‫یحتوي‬ ‫الجهاز‬ ‫العصبي‬ ‫على‬ ‫مجموعتین‬ ‫من‬ ‫الخالیا‬ : ‫الخالیا‬ ‫العصبیة‬ ‫والخالیا‬ ‫الدبقیة‬ •Neurons, or nerve cells, are" excitable cells "that communicate by transmitting electrical impulses . ‫الخالیا‬ ‫العصبیة‬ ، ‫أو‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫هي‬ ‫خالیا‬ ‫قابلة‬ ‫لإلثارة‬ ‫تتواصل‬ ‫مع‬ ‫بعضها‬ ‫البعض‬ ‫عن‬ ‫طریق‬ ‫النبضات‬ ‫الكهربائیة‬ •Excitable cells are defined as cells capable of producing large, rapid electrical signals called action potentials ‫ا‬ ‫لخالیا‬ ‫العصبیة‬ ‫هي‬ ‫الخالیا‬ ‫التي‬ ‫لدیها‬ ‫القدرة‬ ‫على‬ ‫إنتاج‬ ‫إشارات‬ ‫كهربائیة‬ ‫كبیرة‬ ‫وسریعة‬ ( ‫تسمى‬ ‫جهود‬ ‫الفعل‬ ) . •In the nervous system, the neuron is the functional unit ,the smallest unit of a tissue that can carry out the function of that tissue. ‫في‬ ‫الجهاز‬ ‫العصب‬ ‫ي‬ ، ‫الخالیا‬ ‫العصبیة‬ ‫هي‬ ‫وحدات‬ ‫التمثیل‬ ، ‫وهي‬ ‫في‬ ‫الواقع‬ ‫أصغر‬ ‫اللبنات‬ ‫األساسیة‬ ‫لألنسجة‬ ‫العصبیة‬ .
•Glial cells ,which constitute 90% of the cells in the nervous system, provide various types of support to the neurons, including structural and metabolic support ‫تحتوي‬ ‫الخالیا‬ ‫الدبقیة‬ ، ‫التي‬ ‫تشكل‬ 09 ٪ ‫من‬ ‫خالیا‬ ‫الجهاز‬ ‫العصبي‬ ، ‫على‬ ‫مجموعة‬ ‫متنوعة‬ ‫من‬ ‫الوظائف‬ ‫الداعمة‬ ‫للخالیا‬ ‫العصبیة‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ ‫الدعم‬ ‫الهیكلي‬ ‫والتمثیل‬ ‫الغذائي‬ Neurons ‫الخالیا‬ ‫العصبیة‬ •Most neurons contain three main components: ‫تتكون‬ ‫معظم‬ ‫الخالیا‬ ‫العص‬ ‫بیة‬ ‫من‬ ‫ثالثة‬ ‫أجزاء‬ ‫رئیسیة‬ : •A cell body ‫جسم‬ ‫أو‬ ‫جسم‬ ‫الخلیة‬ •Two types of neural processes that extend from the cell body : the dendrite(s) and an axon. ‫نوعان‬ ‫من‬ ‫تكاثر‬ ‫الخالیا‬ ‫التي‬ ‫تركت‬ ‫جسم‬ ‫الخلیة‬ : ‫التشعبات‬ ‫والمحور‬ ‫العصبي‬ •The cell body (or soma) contains the cell nucleus and most of the cell's organelles; ‫یحتوي‬ ‫جسم‬ ‫الخلیة‬ ، ‫أو‬ ‫سوما‬ ، ‫على‬ ‫نواة‬ ‫ومعظم‬ ‫أعضاء‬ ‫الخلیة‬ . •It carries out most of the functions that other cells perform, such as protein synthesis and cellular metabolism . ‫یقوم‬ ‫جسم‬ ‫الخلیة‬ ‫بمعظم‬ ‫األشیا‬ ‫ء‬ ‫التي‬ ‫تقوم‬ ‫بها‬ ‫الخالیا‬ ‫األخرى‬ ، ‫مثل‬ ‫تخلیق‬ ‫البروتین‬ ‫والتمثیل‬ ‫الغذائي‬ ‫الخلوي‬ . •Although they have a nucleus, mature neurons lose the ability to undergo cell division. ‫على‬ ‫الرغم‬ ‫من‬ ‫أن‬ ‫هذه‬ ‫الخالیا‬ ‫لها‬ ‫نوى‬ ، ‫إال‬ ‫أن‬ ‫الخالیا‬ ‫العصبیة‬ ‫البالغة‬ ‫تفتقر‬ ‫إلى‬ ‫القدرة‬ ‫عل‬ ‫ى‬ ‫االنقسام‬ .
•Thus in most areas of the nervous system, adults have all the neurons they will ever have. ‫وهكذا‬ ، ‫في‬ ‫معظم‬ ‫أجزاء‬ ‫الجهاز‬ ‫العصبي‬ ، ‫تبقى‬ ‫الخالیا‬ ‫العصبیة‬ ‫طوال‬ ‫الحیاة‬ . •However, we now know that in a few areas of the adult human brain new neurons can develop from undifferentiated cells (Neurogenesis) ‫ومع‬ ‫ذلك‬ ، ‫فقد‬ ‫أظهرت‬ ‫الدراسات‬ ‫الحدیثة‬ ‫أنه‬ ‫في‬ ‫بعض‬ ‫مناطق‬ ‫الدماغ‬ ‫البشري‬ ‫البالغ‬ ، ‫تتكون‬ ‫الخالیا‬ ‫العصبیة‬ ‫من‬ ‫خالیا‬ ‫غیر‬ ‫متمایزة‬ ‫تكوین‬ ‫الخالیا‬ ‫العصبیة‬ . •Dendrites branch from the cell body and receive input from other neurons at specialized junctions called synapses (Cell bodies themselves can also receive synaptic input). ‫تتفرع‬ ‫التشعبات‬ ‫خارج‬ ‫جسم‬ ‫الخلیة‬ ‫وتتلقى‬ ‫المعلومات‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫األخرى‬ ‫عند‬ ‫وصالت‬ ‫محددة‬ ‫تسمى‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ ( ‫الجسم‬ ‫نفسه‬ ) . ‫تصنع‬ ‫ال‬ ‫خلیة‬ ‫ًا‬‫ض‬‫أی‬ ‫مستقبالت‬ ‫متشابكة‬ •At a synapse, a presynaptic cell releases a chemical messenger called a neurotransmitter that usually communicates with the dendrite or cell body of a postsynaptic cell ‫نام‬ ‫به‬ ‫ویژهای‬ ‫شیمیایی‬ ‫مواد‬ ‫پیشسیناپسی‬ ‫سلول‬ ،‫سیناپس‬ ‫یک‬ ‫در‬ ‫سلولی‬ ‫جسم‬ ‫یا‬ ‫دندریتها‬ ‫با‬ ‫که‬ ‫میکند‬ ‫رها‬ ‫خود‬ ‫از‬ ‫را‬ ‫نوروترانسمیر‬ ‫پس‬ ‫نورون‬- ‫میکند‬ ‫برقرار‬ ‫ارتباط‬ ‫سیناپسی‬ . •Neurons have another branch that comes off the cell body called an axon ,or nerve fiber. ‫للخالیا‬ ‫العصبیة‬ ‫فرع‬ ‫آخر‬ ( ‫یتفرع‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ ) ‫یسمى‬ ‫محور‬ ‫عصبي‬ ‫أو‬ ‫ل‬ ‫یف‬ ‫عصبي‬ . •Unlike a dendrite, whose function is to receive information, an axon's job is to send information. ‫على‬ ‫عكس‬ ‫التشعبات‬ ، ‫تلعب‬ ‫المحاور‬ ‫دور‬ ‫إرسال‬ ‫المعلومات‬ . •Generally, a neuron has only one axon, but axons can branch and thus send signals to more than one destination.
‫عادة‬ ، ‫تحتوي‬ ‫الخلیة‬ ‫العصبیة‬ ‫على‬ ‫محور‬ ‫عصبي‬ ‫واحد‬ ‫فقط‬ ، ‫ولكن‬ ‫یمكن‬ ‫أن‬ ‫یتفرع‬ ‫المحور‬ ‫العصبي‬ ‫ویرسل‬ ‫إشارات‬ ‫إلى‬ ‫أكثر‬ ‫من‬ ‫وجهة‬ ‫واحدة‬ . •The branches of an axon are called collaterals, and like dendrites, the extent of branching varies among neurons and is indicative of the amount of communication with other cells. ‫تسمى‬ ‫الفروع‬ ‫المحوریة‬ ‫الضمانات‬ ، ‫ومثل‬ ‫التشعبات‬ ، ‫یختلف‬ ‫طولها‬ ‫ویشیر‬ ‫إلى‬ ‫مقدار‬ ‫االتصال‬ ‫بالخالیا‬ ‫األخرى‬ . •The axon functions is the transmission of information over relatively long distances in the form of electrical signals called action potentials ‫تتمثل‬ ‫وظیفة‬ ‫المحور‬ ‫العصبي‬ ‫في‬ ‫نقل‬ ‫المعلومات‬ ‫في‬ ‫شكل‬ ‫إشارات‬ ‫كهربائیة‬ ( ‫تسمى‬ ‫إمكانات‬ ‫الفعل‬ ) ‫عبر‬ ‫مسار‬ ‫طویل‬ ‫ًا‬‫ی‬‫نسب‬ . •The beginning and end of an axon are specialized structures called the axon hillock and the axon terminal, respectively. ‫تحتوي‬ ‫بدایة‬ ‫ونهایة‬ ‫المحور‬ ‫العصبي‬ ‫على‬ ‫هیاكل‬ ‫خاصة‬ ‫تسمى‬ ‫نتوءات‬ ‫محور‬ ‫عصبي‬ ‫ومحطات‬ ‫محوریة‬ ، ‫على‬ ‫التوالي‬ . • The axon hillock, the site where the axon originates from the cell body, is specialized in most neurons for the initiation of action potentials . ‫االنتفاخ‬ ‫المحوري‬ ( ‫حیث‬ ‫ینشأ‬ ‫المحور‬ ‫العصبي‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ ) ‫هو‬ ‫المكان‬ ‫الذي‬ ‫یبدأ‬ ‫فیه‬ ‫جهد‬ ‫الفعل‬ . •Once initiated, action potentials are transmitted to the axon terminal. ‫عندما‬ ‫یتم‬ ‫إنشاء‬ ‫جهد‬ ‫الفعل‬ ، ‫یتم‬ ‫توجیه‬ ‫هذه‬ ‫اإلمكانات‬ ‫إلى‬ ‫الم‬ ‫حطة‬ ‫المحوریة‬ . •The axon terminal is specialized to release a neurotransmitter upon arrival of an action potential . ‫خصائص‬ ‫المحطة‬ ‫المحوریة‬ ‫هي‬ ‫أنه‬ ‫عندما‬ ‫یتم‬ ‫الوصول‬ ‫إلى‬ ‫جهد‬ ‫الفعل‬ ، ‫فإنه‬ ‫یطلق‬ ‫الناقل‬ ‫العصبي‬ . •The released neurotransmitter molecules carry a signal to a postsynaptic cell, usually to a dendrite or the cell body of another neuron or to the cells of an effector organ. ‫ترسل‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫التي‬ ‫تم‬ ‫إطالقها‬ ‫إشارة‬ ‫عصبیة‬ ‫إلى‬ ‫خلیة‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫والتي‬ ‫عادة‬ ‫ما‬ ‫تكون‬ ‫التشعبات‬ ‫أو‬ ‫جسم‬ ‫الخلیة‬ ‫للخالیا‬ ‫ال‬ ‫عصبیة‬ ‫أو‬ ‫خالیا‬ ‫العضو‬ ‫التالیة‬ . ‫إنه‬ ‫عملي‬ ، ‫یحترقون‬ .
The opening or closing of ion channels changes the permeability of the plasma membrane for a specific ion, resulting in ion movement across the membrane that causes a change in the electrical properties of the cell or triggers the release of a neurotransmitter .
‫یؤدي‬ ‫إغالق‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ‫إلى‬ ‫تغییر‬ ‫نفاذیة‬ ‫غشاء‬ ‫البالزما‬ ‫لبعض‬ ‫األیونات‬ ‫ونتیجة‬ ‫لذلك‬ ‫تمر‬ ‫األیونات‬ ‫عبر‬ ‫عرض‬ ‫الغشاء‬ ‫وبالتالي‬ ‫یتم‬ ‫تغییر‬ ‫الخصائص‬ ‫الكهربائیة‬ ‫للخلیة‬ ‫أو‬ ‫تحفیز‬ ‫إطالق‬ ‫الن‬ ‫اقالت‬ ‫العصبیة‬ . •Leak channels ,which are found in the plasma membrane throughout a neuron, are always open and are responsible for the resting membrane potential. ‫تكون‬ ‫قنوات‬ ‫التسرب‬ ‫الموجودة‬ ‫في‬ ‫جمیع‬ ‫أجزاء‬ ‫غشاء‬ ‫البالزما‬ ‫العصبیة‬ ‫مفتوحة‬ ‫ا‬ً‫م‬‫دائ‬ ‫وهي‬ ‫مسؤولة‬ ‫عن‬ ‫إ‬ ‫مكانات‬ ‫الراحة‬ ‫للغشاء‬ . •Ligand-gated channels open or close in response to the binding of a chemical messenger to a specific receptor in the plasma membrane. In neurons, ligand-gated channels are located in the dendrites and cell body (areas that receive communication from presynaptic neurons in the form of neurotransmitters). ‫تفتح‬ ‫قنوات‬ Ligand ‫أو‬ ‫تغلق‬ ً‫ة‬‫استجاب‬ ‫الرتباط‬ ‫المواد‬ ‫الكیمیائیة‬ ‫بمستقبالت‬ ‫محددة‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ . ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫قنوات‬ ‫یجند‬ ‫یوجد‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫التشعبات‬ ‫وجسم‬ ‫الخلیة‬ ( ‫المناطق‬ ‫ال‬ ‫تي‬ ‫یتم‬ ‫فیها‬ ‫إجراء‬ ‫الوصالت‬ ‫العصبیة‬ ‫بواسطة‬ ‫الناقالت‬ ‫العصبیة‬ ‫للخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ . ‫منجز‬ •Voltage-gated channels open or close in response to changes in membrane potential. ‫یتم‬ ‫سماع‬ ‫قنوات‬ ‫الجهد‬ ‫استجابة‬ ‫إلمكانیة‬ ‫عمل‬ ‫األغشیة‬ ‫المفتوحة‬ ‫أو‬ ‫المغلقة‬ . •Voltage-gated sodium channels and voltage-gated potassium channels are located throughout the neuron, but most densely in the axon and in greatest density in the axon hillock, and are necessary for the initiation and propagation of action potentials. ‫تنتشر‬ ‫قنو‬ ‫ات‬ ‫جهد‬ ‫الصودیوم‬ ‫والبوتاسیوم‬ ‫في‬ ‫جمیع‬ ‫أنحاء‬ ‫غشاء‬ ‫البالزما‬ ‫العصبیة‬ ، ‫ولكن‬ ‫أعلى‬ ‫كثافة‬ ‫لها‬ ‫تكون‬ ‫في‬ ‫المحاور‬ ، ‫وخاصة‬ ‫االنتفاخ‬ . ‫إنه‬ ‫محور‬ ‫عصبي‬ . ‫هذه‬ ‫القنوات‬ ‫ضروریة‬ ‫لبدء‬ ‫وتوسیع‬ ‫إمكانات‬ ‫العمل‬ . •Voltage-gated calcium channels are located in the axon terminal, these channels open in response to the arrival of an action potential at the axon terminal. When these channels are open, calcium enters the cytosol or the axon terminal and triggers the release of neurotransmitter.
‫توجد‬ ‫قنوات‬ ‫جهد‬ ‫الكالسیوم‬ ‫في‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ‫وتفتح‬ ً‫ة‬‫استجاب‬ ‫إلمكانیة‬ ‫الفعل‬ . ‫عندما‬ ‫تفتح‬ ‫هذه‬ ‫القنوات‬ ، ‫یدخل‬ ‫الكالسیوم‬ ‫إلى‬ ‫الخلیة‬ ‫الخلویة‬ ‫أو‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ‫ویحفز‬ ‫إطالق‬ ‫الناقالت‬ ‫العصبیة‬ . Structural and functional Classification of Neurons ‫التصنیف‬ ‫الهیكلي‬ ‫والوظیفي‬ ‫للخالیا‬ ‫العصبیة‬ Structural Classification of Neurons ‫التصنیف‬ ‫الهیكلي‬ ‫للخالیا‬ ‫العصبیة‬ •Neurons can be classified structurally according to the number of processes (axons and dendrites) that project from the cell body ‫یمكن‬ ‫تصنیف‬ ‫الخالیا‬ ‫العصبیة‬ ‫ًا‬‫ی‬‫هیكل‬ ً‫ء‬‫بنا‬ ‫على‬ ‫عدد‬ ‫المحاور‬ ( ‫المحاور‬ ‫والتشعبا‬ ‫ت‬ ) ‫التي‬ ‫تتفرع‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ . •Unipolar neurons have a single projection from the cell body. ‫الخالیا‬ ‫العصبیة‬ ‫أحادیة‬ ‫القطب‬ ‫لها‬ ‫ملحق‬ ‫بجسم‬ ‫الخلیة‬ . •Bipolar neurons have two projections, an axon and a dendrite, projecting from the cell body. Typical bipolar cells include sensory nenrons for olfaction (smell) and vision. ‫تحتوي‬ ‫الخالیا‬ ‫العصبیة‬ ‫ثنائیة‬ ‫القطب‬ ‫على‬ ‫ملحقین‬ ‫یتفرعان‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ ( ‫محور‬ ‫عصبي‬ ‫وتغصنات‬ ) . ‫هم‬ ‫البصر‬ ‫والرائحة‬ . •Other sensory neurons, including those for touch and pain, are pseudo-unipolar neurons, a subclass of bipolar neurons. Although only one process seems to extend in two directions from the cell body, there are actually two processes, an axon and a modified dendrite, that project from the cell body in opposite directions. The modified dendritic process is called the peripheral axon because it originates in the periphery with sensory receptors and functions as an axon in that it transmits action potentials. The axon process is called the central axon because it ends in the central nervous system, where it forms synapses with other neurons. ‫الخالیا‬ ‫العصبیة‬ ‫الحسیة‬ ‫األخرى‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ ‫العمود‬ ‫الفقري‬ ‫واأللم‬ ، ‫هي‬ ‫الخالیا‬ ‫العصبیة‬ ‫القطبیة‬ ‫الزائفة‬ ( ‫مجموعة‬ ‫فرعیة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫ثنائیة‬ ‫القطب‬ ) ، ‫على‬ ‫الرغم‬ ‫من‬ ‫أنها‬ ‫تبدو‬ ‫فقط‬
‫تغادر‬ ‫إحدى‬ ‫الزوائد‬ ‫جسم‬ ‫ال‬ ‫خلیة‬ ‫وتستمر‬ ‫في‬ ‫اتجاهین‬ ، ‫ولكن‬ ‫هناك‬ ‫بالفعل‬ ‫ملحقان‬ ، ‫أحدهما‬ ‫محوار‬ ‫واآلخر‬ ‫شجیري‬ ، ‫في‬ ‫كال‬ ‫االتجاهین‬ . ‫تستمر‬ ‫األضداد‬ . ‫تسمى‬ ‫هذه‬ ‫التشعبات‬ ‫الخاصة‬ ‫بالمحاور‬ ‫الطرفیة‬ ‫ألنها‬ ‫تنشأ‬ ‫من‬ ‫المستقبالت‬ ‫الحسیة‬ ، ‫ومثل‬ ‫المحاور‬ ، ‫تنقل‬ ‫جهد‬ ‫الفعل‬ . ‫زایده‬ ‫ُطلق‬‫ی‬ ‫على‬ ‫المحوار‬ ‫ًا‬‫ض‬‫أی‬ ‫اسم‬ ‫محو‬ ‫ر‬ ‫عصبي‬ ‫مركزي‬ ‫ألنه‬ ‫ینتهي‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫ویتشابك‬ ‫مع‬ ‫الخالیا‬ ‫العصبیة‬ ‫األخرى‬ ‫في‬ ‫هذه‬ ‫المنطقة‬ . •Multipolar neurons, the most common neurons, have multiple projections from the cell body; one projection is an axon, all the others are dendrites ‫تحتوي‬ ‫الفیرونات‬ ‫متعددة‬ ‫األقطاب‬ ، ‫والتي‬ ‫تعد‬ ‫ًا‬‫ض‬‫أی‬ ‫أكثر‬ ‫أنواع‬ ‫الخالیا‬ ‫العصبیة‬ ‫ًا‬‫ع‬‫شیو‬ ، ‫على‬ ‫العدید‬ ‫من‬ ‫الزوائد‬ ‫في‬ ‫جسم‬ ‫الخلیة‬ . ‫أحد‬ ‫هذه‬ ‫االمتدادات‬ ‫هو‬ ‫محور‬ ‫عصبي‬ ‫والباقي‬ ‫هو‬ ‫التشعبات‬ ‫نكون‬ .
Functional Classification of Neurons ‫التصنیف‬ ‫الوظیفي‬ ‫للخالیا‬ ‫العصبیة‬ •There are three functional classes of neurons : •Efferent neurons ‫الخالیا‬ ‫العصبیة‬ ‫المرنة‬ •Afferent neurons ‫الخالیا‬ ‫العصبیة‬ ‫األفارانیة‬ • Interneurons. ‫الخالیا‬ ‫العصبیة‬ ‫الوسیطة‬ Efferent neurons transmit information from the central nervous system to effector organs. ‫تنقل‬ ‫الخالیا‬ ‫العصبیة‬ ‫الصادرة‬ ‫المعلومات‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫إلى‬ ‫األعضاء‬ ‫النشطة‬ . • Recall that efferent neurons include the motor neurons extending to skeletal muscle and neurons of the autonomic nervous system
‫وتجدر‬ ‫اإلشارة‬ ‫إلى‬ ‫أن‬ ‫الخالیا‬ ‫ال‬ ‫عصبیة‬ ‫الصادرة‬ ‫تشمل‬ ‫الخالیا‬ ‫العصبیة‬ ‫الحركیة‬ ( ‫العضالت‬ ‫الهیكلیة‬ ) ‫والخالیا‬ ‫العصبیة‬ ANS • The cell body and dendrites of efferent neurons are located in the central nervous system (autonomic postganglionic neurons, are an exception). ‫یقع‬ ‫جسم‬ ‫الخلیة‬ ‫والتشعبات‬ ‫ل‬ ‫لخالیا‬ ‫العصبیة‬ ‫الصادرة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ( ‫الخالیا‬ ‫العصبیة‬ ‫االرتجاعیة‬ ‫الالإرادیة‬ ‫هي‬ ‫استثناء‬ ) . • The axon leaves the central nervous system and becomes part of the peripheral nervous system as it travels to the effector organ it innervates ‫تغادر‬ ‫محاو‬ ‫ر‬ ‫هذه‬ ‫الخالیا‬ ‫العصبیة‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫وكجزء‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ (PNS) ‫تذهب‬ ‫إلى‬ ‫األعضاء‬ ‫النشطة‬ ‫وتعصبها‬ . •The function of afferent neurons is to transmit either sensory information from sensory receptors (which detect information pertaining to the outside environment) or visceral information from visceral receptors (which detect information pertaining to conditions in the interior of the body) to the central nervous system for further processing . ‫تتمثل‬ ‫وظیفة‬ ‫الخالیا‬ ‫العصبیة‬ ‫الواردة‬ ‫في‬ ‫نقل‬ ‫المعلوم‬ ‫ات‬ ‫الحسیة‬ ‫من‬ ‫المستقبالت‬ ‫الحسیة‬ ( ‫التي‬ ‫تأخذ‬ ‫المعلومات‬ ‫من‬ ‫البیئة‬ ) ‫أو‬ ‫المعلومات‬ ‫الحشویة‬ ‫من‬ ‫المستقبالت‬ ‫یتم‬ ‫إرسال‬ ‫األحشاء‬ ( ‫التي‬ ‫تتلقى‬ ‫معلومات‬ ‫حول‬ ‫الظروف‬ ‫الداخلیة‬ ‫للجسم‬ ) ‫إلى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫لمزید‬ ‫من‬ ‫المعالجة‬ . •Most afferent neurons are pseudo-unipolar neurons ,with the cell body located outside the central nervous system in a ganglion (the general term for a cluster of neural cell bodies located outside the CNS) ‫معظم‬ ‫الخالیا‬ ‫العصبیة‬ ‫الواردة‬ ‫هي‬ ‫عصبونات‬ ‫زائفة‬ ‫أحادیة‬ ‫القطب‬ ‫تكون‬ ‫أجسامها‬ ‫الخلویة‬ ‫خارج‬ ‫الجهاز‬ ‫الع‬ ‫صبي‬ ‫المركزي‬ ‫وفي‬ ‫العقد‬ ‫العصبیة‬. ‫من‬ ‫الشائع‬ ‫أن‬ ‫تتراكم‬ ‫أجسام‬ ‫الخالیا‬ ‫خارج‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ . •The endings of the peripheral axon are located in the peripheral organ (sensory organ or visceral organ), where they are either modified into sensory receptors or receive communication from separate sensory receptor cells . ‫تقع‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ‫المحیطي‬ ‫في‬ ‫األعضاء‬ ‫المحیطیة‬ ( ‫األعضاء‬ ‫الحسیة‬ ‫أو‬ ‫الحشویة‬ ) ، ‫أي‬ ‫حیث‬ ‫تذهب‬ ‫إلى‬ ‫المستقبالت‬ ‫الحسیة‬ ‫أو‬ ‫تجري‬ ‫اتصاالت‬ . ‫یتلقون‬ ‫مستقبالت‬ ‫حسیة‬ ‫منفصلة‬ ‫من‬ ‫الخالیا‬ .
•The central axon terminates in the central nervous system, where it releases a neurotransmitter to communicate with other neurons. ‫ینتهي‬ ‫المحور‬ ‫المركزي‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ، ‫حیث‬ ‫یطلق‬ ‫نواقله‬ ‫العصبیة‬ ‫للتواصل‬ ‫مع‬ ‫الخالیا‬ ‫العصبیة‬ ‫األخرى‬ . •The third functional class of neurons is interneurons ,which account for 99% of all neurons in the body . ‫المجموعة‬ ‫الثالثة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ( ‫وظیفیا‬ ) ‫هي‬ ‫الخالیا‬ ‫العصبیة‬ ‫الوسیطة‬ ‫التي‬ ‫تشكل‬ 00 ٪ ‫من‬ ‫مجموع‬ ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجسم‬ . •They are located entirely in the central nervous system . ‫تقع‬ ‫بالكامل‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ . •Interneurons perform all the functions of the central nervous system ,including processing sensory information from afferent neurons, sending out commands to effector organs through efferent neurons, and carrying out complex functions of the brain such as thought, memory, and emotions. ‫الخالیا‬ ‫العصبیة‬ ‫الوسیطة‬ ‫جمیع‬ ‫وظائف‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ ‫معالجة‬ ‫المعلومات‬ ‫الحسیة‬ ‫الواردة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫الواردة‬ ، ‫وإرسال‬ ‫األوامر‬ ‫إلى‬ ‫األعضاء‬ ‫النشطة‬ . ‫من‬ ‫خالل‬ ‫الخالیا‬ ‫ا‬ ‫لعصبیة‬ ‫الصادرة‬ ، ‫وتؤدي‬ ‫العدید‬ ‫من‬ ‫وظائف‬ ‫الدماغ‬ ‫المعقدة‬ ‫مثل‬ ‫التفكیر‬ ‫والذاكرة‬ ‫والعواطف‬ .
Structural Organization of Neurons in the Nervous System ‫التنظیم‬ ‫الهیكلي‬ ‫للخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ •Structural Organization of Neurons in the Nervous System Neurons are arranged within the nervous system in an orderly fashion, with those having similar functions tending to be grouped together. ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫لها‬ ‫ترتیب‬ ‫هرمي‬ ، ‫وتلك‬ ‫التي‬ ‫تعمل‬ ‫بشكل‬ ‫مشابه‬ ‫تشكل‬ ‫مجموعات‬ . •Neurons are aligned in such a way that cell bodies and dendrites of adjacent cells tend to be grouped together, and axons of adjacent cells tend to be grouped together.
‫یتم‬ ‫ترتیب‬ ‫الخالیا‬ ‫العصبیة‬ ‫بحیث‬ ‫تشكل‬ ‫أجسام‬ ‫الخالیا‬ ‫والتشعبات‬ ‫للخالیا‬ ‫المجاورة‬ ‫مجموعة‬ ‫مع‬ ‫بعضها‬ ‫البعض‬ ، ‫ومحاور‬ ‫للخالیا‬ ‫المجاورة‬ ‫هم‬ ‫أیضا‬ ‫یشكلون‬ ‫مجموعات‬ ‫مع‬ ‫بعضهم‬ ‫البعض‬ •In the central nervous system ,cell bodies of neurons are often grouped into nuclei (singular = nucleus), and the axons travel together in bundles called pathways, tracts, or commissures. ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ، ‫ًا‬‫ب‬‫غال‬ ‫ما‬ ‫تتجمع‬ ‫أجسام‬ ‫الخالیا‬ ‫العصبیة‬ ‫داخل‬ ‫النوى‬ ، ‫وتتجمع‬ ‫المحاور‬ ‫في‬ ‫مجموعات‬ ‫تسمى‬ ‫المسارات‬ ‫أو‬ ‫الوصالت‬ ‫أو‬ ‫التقاطعات‬ . ‫وجدت‬ . •In the peripheral nervous system ,cell bodies of neurons are clustered together in ganglia (singular = ganglion), and the axons travel together in bundles called nerves ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ ، ‫تتجمع‬ ‫أجسام‬ ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫عقد‬ ، ‫وتتجمع‬ ‫المحاور‬ ‫في‬ ‫مجموعات‬ ‫تسمى‬ ‫األعصاب‬ . Glial Cells ‫الخالیا‬ ‫الدبقیة‬ •Glial cells ,the second class of non-neural cells found in the nervous system, account for 90% of all cells in the nervous system. ‫الخالیا‬ ‫الدبقیة‬ - ‫ثاني‬ ‫أكبر‬ ‫مجموعة‬ ‫من‬ ‫الخالیا‬ ‫غیر‬ ‫العصبیة‬ ‫الموجودة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ - 09 ٪ ‫من‬ ‫جمیع‬ ‫الخالیا‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫یعطون‬ . •They do not function directly in signal transmission; instead, they provide structural integrity to the nervous system (glia is Latin for "glue”) and they are necessary for neurons to carry out their functions. ‫ال‬ ‫تلعب‬ ‫هذه‬ ‫الخالیا‬ ‫ا‬ ً‫دور‬ ‫ا‬ً‫مباشر‬ ‫في‬ ‫نقل‬ ‫اإلشارات‬ ‫العصبیة‬ ، ‫ولكنها‬ ً‫ال‬‫بد‬ ‫من‬ ‫ذلك‬ ‫توفر‬ ‫قوة‬ ‫هیكلیة‬ ‫للجهاز‬ ‫ا‬ ‫لعصبي‬ ‫إنه‬ ‫یعني‬ ‫الغراء‬ ( ‫وبالتالي‬ ‫فهو‬ ‫ضروري‬ ‫للتشغیل‬ ‫السلیم‬ ‫للخالیا‬ ‫العصبیة‬ .
•There are five types of glial cells: •Astrocytes •Eependymal cells •Microglia •Oligodendrocytes •Schwann cells ‫هناك‬ ‫خمسة‬ ‫أنواع‬ ‫من‬ ‫الخالیا‬ ‫الدبقیة‬ : * ‫الخالیا‬ ‫القشریة‬ ‫أو‬ ‫الخال‬ ‫یا‬ ‫النجمیة‬ * ‫خالیا‬ ‫البطانة‬ ‫العصبیة‬ * ‫الخالیا‬ ‫الدبقیة‬ ‫الصغیرة‬ * ‫خالیا‬ Oligodendron * ‫خالیا‬ ‫شوان‬
Astrocytes are critical role in formation of the blood-brain barrier (they stimulate endothelial cells to develop tight junctions by unknown mechanisms). ‫تل‬ ‫عب‬ ‫الخالیا‬ ‫القشریة‬ ‫ا‬ً‫دور‬ ‫ا‬ً‫م‬‫مه‬ ‫في‬ ‫تكوین‬ ‫الحاجز‬ ‫الدموي‬ ‫الدماغي‬ ، ‫فهي‬ ‫تحفز‬ ‫الخالیا‬ ‫البطانیة‬ ‫على‬ ‫تكوین‬ ‫روابط‬ ‫بواسطة‬ ‫آلیة‬ ‫غیر‬ ‫معروفة‬ . ‫تصبح‬ ‫صعبة‬ •Ependymal cells that lining the ventricles and central canal of CNS, are a type of epithelial cell ‫الخالیا‬ ‫البطان‬ ‫یة‬ ‫العصبیة‬ ‫التي‬ ‫تبطن‬ ‫بطینات‬ ‫الدماغ‬ ‫والقناة‬ ‫المركزیة‬ ‫للجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫هي‬ ‫ظهاریة‬ . •Microglial cells are part of the supporting structure of CNS that are migratory and phagocytic (phagocyte the waste products of nerve tissue in CNS) ‫الخالیا‬ ‫الدبقیة‬ ‫الصغ‬ ‫یرة‬ ‫هي‬ ‫جزء‬ ‫من‬ ‫الهیكل‬ ‫الوقائي‬ ‫للجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫ولها‬ ‫خاصیة‬ ‫الهجرة‬ ‫والبلعمة‬ ( ‫البلعمة‬ ) ‫من‬ ‫إفرازات‬ ‫األنسجة‬ ‫العصبیة‬ ‫في‬ CNS) ‫لها‬
•Oligodendrocytes and Schwann cells are crucial role in electrical transmission of neurons ‫تلعب‬ ‫خالیا‬ Oligodendral ‫و‬ Schwann ‫دو‬ ‫ا‬ً‫ر‬ ‫ا‬ً‫م‬‫مه‬ ‫في‬ ‫النقل‬ ‫الكهربائي‬ ‫للخالیا‬ ‫العصبیة‬ •The primary function of oligodendrocytes and Schwann cells is to form an insulating wrap of myelin around the axons of neurons. ‫یتمثل‬ ‫الدور‬ ‫الرئیسي‬ ‫لخالیا‬ oligodendral ‫و‬ Schwann ‫في‬ ‫إنشاء‬ ‫غمد‬ ‫المایلین‬ ‫حول‬ ‫المح‬ ‫اور‬ ‫العصبیة‬ •Such insulation enables neurons to transmit action potentials more efficiently and rapidly. ‫تزید‬ ‫هذه‬ ‫العزلة‬ ‫من‬ ‫سرعة‬ ‫وكفاءة‬ ‫انتقال‬ ‫الفعل‬ ‫المحتمل‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ . •Myelin consists of concentric layers of the cell membranes of either oligodendrocytes or Schwann cells ‫یحتوي‬ ‫المیالین‬ ‫على‬ ‫طبقات‬ ‫متحدة‬ ‫المركز‬ ‫من‬ ‫أغشیة‬ ‫الخالیا‬ ‫لخالیا‬ ‫قلیلة‬ ‫التغصن‬ ‫وخالیا‬ ‫شوان‬ . •Oligodendrocytes form myelin around axons in the central nervous system ‫تشكل‬ ‫الخالیا‬ ‫قلیلة‬ ‫التغصن‬ ‫غشاء‬ ‫المایلین‬ ‫حول‬ ‫محاور‬ ‫عصبیة‬ ‫في‬ ‫الجهاز‬ ‫الع‬ ‫صبي‬ ‫المركزي‬ . •One oligodendrocyt sends out projections providing the myelin segments for many axons ‫تنضح‬ ‫خلیة‬ oligodendron ‫الزوائد‬ ‫التي‬ ‫تشكل‬ ‫غشاء‬ ‫المایلین‬ ‫لعدة‬ ‫محاور‬ •Schwann calls form myelin around axons in the peripheral nervous system ,but each Schwann cell provides myelin for only one axon ‫تشكل‬ ‫خالیا‬ ‫شوان‬ ‫غشاء‬ ‫المایلین‬ ‫على‬ ‫المحاور‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ ، ‫لكن‬ ‫كل‬ ‫خلیة‬ ‫شوان‬ ‫تنتج‬ ‫ا‬ً‫محوار‬ ‫ًا‬‫د‬‫واح‬ ‫فقط‬ ‫من‬ ‫غشاء‬ ‫المایلین‬ . ‫یفعل‬ . •Many oligodendrocytes or Schwann cells are needed to provide the myelin for a single axon. ‫هناك‬ ‫حاجة‬ ‫إلى‬ ‫عدة‬ ‫خالیا‬ oligodendron ‫أو‬ Schwann ‫إلنتاج‬ ‫المایلین‬ ‫من‬ ‫محور‬ ‫عصبي‬ •Because the lipid bilayer of a cell membrane has low permeability to ions, the several layers of membrane that make up a myelin sheath substantially reduce leakage of ions across the cell membrane ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫الغشاء‬ ‫الخلوي‬ ‫ثنائي‬ ‫الطبقة‬ ‫الدهنیة‬ ‫له‬ ‫نفاذیة‬ ‫منخفضة‬ ‫لألیونات‬ ، ‫یمكن‬ ‫أن‬ ‫تكون‬ ‫طبقات‬ ‫عدیدة‬ ‫من‬ ‫غشاء‬ ‫الخلیة‬ ‫التي‬ ‫یتكون‬ ‫منها‬ ‫غشاء‬ ‫المایلین‬ ‫بشكل‬ ‫ملحوظ‬ ‫یقلل‬ ‫بشكل‬ ‫كبیر‬ ‫من‬ ‫نفاذیة‬ ‫األیونات‬ ‫من‬ ‫غشاء‬ ‫الخلیة‬ ‫للخالیا‬ ‫العصبیة‬ .
•However in gaps in the myelin, called nodes of Ranvier ,The axonal membrane contains voltage-gated sodium and potassium channels that function in the transmission of action potentials by allowing ion movement across the membrane. ‫ومع‬ ‫ذلك‬ ، ‫في‬ ‫مناطق‬ ‫من‬ ‫غشاء‬ ‫ا‬ ‫لمیالین‬ ‫تسمى‬ ‫العقد‬ ‫الكلویة‬ ، ‫یحتوي‬ ‫غشاء‬ ‫المحور‬ ‫العصبي‬ ‫على‬ ‫قنوات‬ ‫جهد‬ ‫الصودیوم‬ ‫والبوتاسیوم‬ ‫التي‬ ‫تمر‬ ‫عبرها‬ . ‫األیونات‬ ‫تنقل‬ ‫الجهد‬ ‫من‬ ‫الغشاء‬ .
Types of nerve fiber ‫أنواع‬ ‫األلیاف‬ ‫العصبیة‬ •A fibers : ‫ألیاف‬ ‫من‬ ‫النوع‬ ‫أ‬ •Myelinated afferent or efferent fibers of somatic nervous system having a diameter of 2 to 20 micron and conduction velocity of 12 to 120 meter per second; they include alpha, beta, gamma and delta fibers
‫األفاران‬ ‫واأللیاف‬ ‫النخاعیة‬ ‫الصادرة‬ ، ‫الجهاز‬ ‫العصبي‬ ، SNS ( ‫ا‬ ‫لجسم‬ ( 2 ‫إلى‬ 29 ‫میكرون‬ ‫في‬ ‫القطر‬ ‫و‬ 22 ‫إلى‬ 229 ‫ا‬ً‫متر‬ ‫في‬ ‫الثانیة‬ ) ‫وهي‬ ‫تشمل‬ ‫ألفا‬ ‫وبیتا‬ ‫وجاما‬ ‫ودلتا‬ . •A alpha fibers : ‫ألیاف‬ ‫نوع‬ ‫ألفا‬ •Motor and proprioceptive fibers of the A type having conduction velocities of 70 to 120 meter per second and ranging from 12 to 20 micron in diameter ‫نوع‬ ‫ألفا‬ ‫أ‬ : ‫األلیاف‬ ‫الحسیة‬ ‫والحسیة‬ ‫العمیقة‬ ، ‫استقبال‬ ‫الرسائل‬ ‫الحسیة‬ ‫من‬ ‫أعماق‬ ‫الجسم‬ ( ‫النوع‬ ‫أ‬ ، ‫بمعدل‬ ‫نقل‬ ‫من‬ 09 ‫إلى‬ 229 ‫متر‬ ‫في‬ ‫الثانیة‬ ‫واألقطار‬ ‫من‬ 22 ‫إلى‬ 29 ‫میكرون‬ . •A beta fibers : •Motor and proprioceptive fibers of the A type having conduction velocities of 30 to 70 meter per second and ranging from 5 to 12 micron in diameter ‫ألیاف‬ ‫بیتا‬ ‫من‬ ‫النوع‬ A: ‫محرك‬ ‫عمیق‬ ‫وألیاف‬ ‫حسیة‬ ‫لها‬ ‫معدل‬ ‫نقل‬ ‫من‬ 09 ‫إلى‬ 09 ‫متر‬ ‫في‬ ‫الثانیة‬ ‫وقطر‬ ‫من‬ 5 ‫إلى‬ 22 ‫میكرون‬ •A gamma fibers : •Fibers of the A type having conduction velocities of 15 to 30 meter per second and ranging from 3 to 6 micron in diameter. These fiber are fusimotor fiber (modified muscle fibers which surrounded by fluid and enclosed in connective tissue envelope, compose the muscle spindle). ‫ألیا‬ ‫ف‬ ‫جاما‬ ‫من‬ ‫النوع‬ ‫أ‬ : ‫سرعة‬ ‫النقل‬ ‫من‬ 25 ‫إلى‬ 09 ‫متر‬ ‫في‬ ‫الثانیة‬ ‫وقطرها‬ ‫من‬ 0 ‫إلى‬ 6 ‫میكرون‬ . ‫هذه‬ ‫األلیاف‬ ‫هي‬ ‫ألیاف‬ fusimotor ‫عضالت‬ ‫مشوهة‬ ‫محاطة‬ ‫بسائل‬ ‫وتقع‬ ‫في‬ ‫غمد‬ ‫من‬ ‫النسیج‬ ‫الضام‬ . •A delta fibers : •A type of small myelinated afferent A fibers that respond to pressure, temperature, or chemical stimuli, conducting from the cutaneous tissues the initial stimulus perceived as the primary painful event. Their conducting velocity is low, about the same as that of B fibers ‫ألیاف‬ ‫دلتا‬ ‫من‬ ‫النوع‬ A: ‫نوع‬ ‫من‬ ‫األلیاف‬ A ‫تكون‬ ‫صادرة‬ ‫ومخلفة‬ ‫وتستجیب‬ ‫لمحفزات‬ ‫انضغاطیة‬ ‫أو‬ ‫حراریة‬ ‫أو‬ ‫كیمیائیة‬ ‫من‬ ‫أنسجة‬ ‫الجلد‬ ‫معدل‬ ‫نقل‬ ‫هذه‬ ‫األلیاف‬ ‫منخفض‬ ‫وحوالي‬ ‫األلیاف‬ ‫ب‬ . •B fibers : ‫ألیاف‬ ‫ب‬
•Myelinated preganglionic autonomic axons having conduction velocities of 3 to 15 meter per second and ranging from 1 to 3 micron in diameter. ‫محاور‬ ‫أمامیة‬ ‫ذاتیة‬ ‫النخاع‬ ‫بسرعة‬ ‫نقل‬ ‫من‬ 0 ‫إلى‬ 25 ‫ا‬ ً‫متر‬ ‫في‬ ‫الثانیة‬ ‫وقطرها‬ ‫من‬ 2 ‫إلى‬ 0 ‫میكرون‬ . •These include only efferent fibers ‫هذه‬ ‫األلیاف‬ ‫هي‬ ‫فقط‬ ‫من‬ ‫النوع‬ ‫الصادر‬ . •C fibers : ‫ألیاف‬ ‫ج‬ •Unmyelinated nerve fibers, having slower conduction velocities (0.7 to 2.3 meter per second) and smaller diameter (0.3 to 1.3 micron) than alpha fibers ‫ألیاف‬ ‫غیر‬ ‫المیالنین‬ ‫ذات‬ ‫معدل‬ ‫نقل‬ ‫أقل‬ ( 0.9 ‫إلى‬ 0.2 ‫م‬ / ‫ث‬ ( ‫وقطرها‬ ‫أصغر‬ ‫من‬ ‫ألیاف‬ ‫ألفا‬ ( ) 0.9 ‫إلى‬ 0.2 ‫میكرومتر‬ ) • They are found as postganglionic (efferent) fibers of the autonomic nervous system, and as afferent fibers at as thermoreceptors, nociceptors, and interoceptors ‫عرف‬ُ‫ت‬ ‫هذه‬ ‫األلیاف‬ ‫باأللیاف‬ ‫التبخیریة‬ ‫المرتجعة‬ ‫لنظام‬ ANS ‫واأللیاف‬ ‫الواردة‬ ‫مثل‬ ‫المستقبالت‬ ‫الحراریة‬ ‫وأعصاب‬ ‫األلم‬ ‫واألعصاب‬ ‫الحشویة‬ .
Neural Integration ‫االستمراریة‬ ‫العصبیة‬ •Communication between neuruns, however, is not a one-to-one relationship ‫االتصال‬ ‫بین‬ ‫الخالیا‬ ‫العصبیة‬ ‫لیس‬ ‫مجرد‬ ‫اتصال‬ ‫واحد‬ ‫لواحد‬ .
•In some cases many neurons communicate with a given neuron, an arrangement called convergence ‫في‬ ‫بعض‬ ‫الحاالت‬ ، ‫ترتبط‬ ‫العدید‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫بخالیا‬ ‫عصبیة‬ ‫واحدة‬ ، ‫وهو‬ ‫ترتیب‬ ‫یسمى‬ ‫التقارب‬ . •In convergence, a neuron must function as an integrator ,taking in informalion from several different sources in the form of graded potentials ,summing it, and then on the basis of the results, either generating an action potential or not ‫عند‬ ‫التقارب‬ ، ‫تعمل‬ ‫الخلیة‬ ‫العصبیة‬ ‫كمولد‬ ‫للتحالف‬ ، ‫وتجمع‬ ‫المعلومات‬ ‫من‬ ‫عدة‬ ‫مصادر‬ ‫مختلفة‬ ‫ثم‬ ‫أ‬ ‫یخلق‬ ‫إمكانات‬ ‫فعلیة‬ ( ‫أو‬ ‫ال‬ ‫تخلق‬ ‫إمكانات‬ ‫فعلیة‬ ) . •In other cases the axon of one neuron branches into many terminals that communicate with many other cells, an arrangement called divergence ‫في‬ ‫حاالت‬ ‫أخرى‬ ، ‫یقسم‬ ‫المحور‬ ‫العصبي‬ ‫الخالیا‬ ‫العصبیة‬ ‫إلى‬ ‫عدة‬ ‫فروع‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫تكوین‬ ‫ترتیب‬ ‫یسمى‬ ‫متشعب‬ .
SYNAPSES ‫المشابك‬ TYPES OF SYNAPSES ‫أنواع‬ ‫المشابك‬
•Neurons communicate at specialized structures called synapses. ‫تتواصل‬ ‫الخالیا‬ ‫العصبیة‬ ‫مع‬ ‫بعضها‬ ‫البعض‬ ‫في‬ ‫هیاكل‬ ‫خاصة‬ ‫تسمى‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ . •There are two types of synapses in the nervous system: ‫هناك‬ ‫نوعان‬ ‫من‬ ‫نقاط‬ ‫االشتباك‬ ‫ال‬ ‫عصبي‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ . •Electrical synapses •Chemical synapses • ‫المشابك‬ ‫الكهربائیة‬ • ‫المشابك‬ ‫الكیمیائیة‬ Electrical synapses Electrical synapses operate by allowing electrical signals to be transmitted directly from one neuron to another ;neurotransmitters are not involved . ‫تسمح‬ ‫المشابك‬ ‫الكهربائیة‬ ‫بنقل‬ ‫اإلشارات‬ ‫الكهربائیة‬ ‫مباشرة‬ ‫من‬ ‫خلیة‬ ‫عصبیة‬ ‫إلى‬ ‫أخرى‬ ‫دون‬ ‫استخدام‬ ‫الناقالت‬ ‫العصبیة‬ . •At these synapses the plasma membranes of adjacent cells are linked together by gap junctions such that when an electrical signal, such as an action potential, is generated in one cell, it is directly transferred to the adjacent cell by means of ions flowing through the gap junctions. ‫في‬ ‫هذه‬ ‫المشابك‬ ، ‫ترتبط‬ ‫أغشیة‬ ‫البالزما‬ ‫لخلیتین‬ ‫متجاورتین‬ ‫عن‬ ‫طریق‬ ‫وصالت‬ ‫وإشارة‬ ‫كهربائیة‬ ( ‫مثل‬ ‫یتم‬ ‫نقل‬ ‫جهد‬ ‫الفعل‬ ( ‫الذي‬ ‫تم‬ ‫إنشاؤه‬ ‫في‬ ‫خلیة‬ ‫مباشرة‬ ‫إلى‬ ‫الخلیة‬ ‫المجاورة‬ ) ‫عن‬ ‫طریق‬ ‫تدفق‬ ‫األیونات‬ ‫من‬ ‫فجوة‬ ‫الوصلة‬ . •Because the function of electrical synapses in the nervous system is not well understood, they will not be discussed any further here. ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫وظیفة‬ ‫المشابك‬ ‫الكهربائیة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫لم‬ ‫یتم‬ ‫توضیحها‬ ‫بشكل‬ ‫صحیح‬ ‫بعد‬ ، ‫فلن‬ ‫یتم‬ ‫شرحها‬ ‫بمزید‬ ‫من‬ ‫التفصیل‬ ‫هنا‬ . •However, gap junctions in smooth and cardiac muscle have an important role in enabling these muscles to contract as a unit .
‫فجوات‬ ‫التقاطع‬ ‫في‬ ‫ال‬ ‫عضالت‬ ‫الملساء‬ ‫وعضلة‬ ‫القلب‬ ‫لها‬ ‫دور‬ ‫مهم‬ ‫في‬ ‫تقلص‬ ‫هذه‬ ‫العضالت‬ ( ‫كوحدة‬ ) . CHEMICAL SYNAPSES ‫المشابك‬ ‫الكیمیائیة‬ •Almost all neurons transmit messages to other cells at chemical synapses. ‫تنقل‬ ‫جمیع‬ ‫الخالیا‬ ‫العصبیة‬ ‫ًا‬‫ب‬‫تقری‬ ‫رسائلها‬ ‫إلى‬ ‫الخالیا‬ ‫األخرى‬ ‫من‬ ‫خالل‬ ‫المشاب‬ ‫ك‬ ‫الكیمیائیة‬ . •In a chemical synapse, one neuron secretes a neurotransmitter into the extracellular fluid in response to an action potential arriving at its axon terminal . ‫في‬ ‫المشابك‬ ‫الكیمیائیة‬ ، ‫تفرز‬ ‫الخالیا‬ ‫العصبیة‬ ‫نقاط‬ ‫نهایة‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫السائل‬ ‫خا‬ ‫رج‬ ‫الخلیة‬ ً‫ة‬‫استجاب‬ ‫لقدرتها‬ ‫على‬ ‫الفعل‬ . ‫یفعل‬ . •The neurotransmitter then binds to receptors on the plasma membrane of a second cell, triggering in that cell an electrical signal that may or may not initiate an action potential, depending on a number of circumstances. ‫ثم‬ ‫یتصل‬ ‫الناقل‬ ‫العصبي‬ ‫بمستقبالت‬ ‫معینة‬ ‫على‬ ‫غشاء‬ ‫البالزما‬ ‫للخلیة‬ ‫الثانیة‬ ، ‫مما‬ ‫ینتج‬ ‫عنه‬ ‫إشارة‬ ‫كهربائیة‬ ‫قد‬ ‫قد‬ ‫یؤدي‬ ‫أو‬ ‫ال‬ ‫یؤدي‬ ‫إلى‬ ‫إجراء‬ ‫محتمل‬ ( ‫حسب‬ ‫ظروف‬ ‫معینة‬ ) . •A neuron can form synapses with other neurons or with effector cells such as muscle or gland cells. ‫یمكن‬ ‫أن‬ ‫تتكون‬ ‫الخالیا‬ ‫العصبیة‬ ‫مع‬ ‫خالیا‬ ‫عصبیة‬ ‫أخرى‬ ‫أو‬ ‫خالیا‬ ‫وظیفیة‬ ‫مثل‬ ‫خالیا‬ ‫العضالت‬ ‫أو‬ ‫الغدد‬ ‫المشبكیة‬ . •Muscles and glands are generally referred to as effector organs, and a synapse between a neuron and an effector cell is called a neuroeffector junction. ‫تسمى‬ ‫العضالت‬ ‫والغدد‬ ‫عادة‬ ‫باألعضاء‬ ‫العاملة‬ ، ‫ُطلق‬‫ی‬‫و‬ ‫على‬ ‫المشبك‬ ‫بین‬ ‫الخلیة‬ ‫العصبیة‬ ‫والخلیة‬ ‫العاملة‬ ‫تقاطع‬ ‫العامل‬ ‫العصبي‬ . •Neuroeffector junctions operate according to the same basic principles concerning neuron-to-neuron synapses. ‫تعمل‬ ‫اتصاال‬ ‫ت‬ ‫العوامل‬ ‫العصبیة‬ ‫ا‬ً‫ق‬‫وف‬ ‫لنفس‬ ‫المبادئ‬ ‫التي‬ ‫تحكم‬ ‫المشابك‬ ‫العصبیة‬ . •In a few instances, non-neuronal cells can form synapses with neurons, as occurs ,for example, with taste receptor cells in taste buds on the tongue
‫في‬ ‫حاالت‬ ‫نادرة‬ ، ‫یمكن‬ ‫للخالیا‬ ‫غیر‬ ‫العصبیة‬ ‫تشكیل‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ ‫مع‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫مثل‬ ‫المشابك‬ ‫مع‬ ‫خالیا‬ ‫مستقبالت‬ ‫الذوق‬ ‫في‬ ‫براعم‬ ‫التذوق‬ . Functional Anatomy of Chemical Synapses ‫التشریح‬ ‫الوظیفي‬ ‫للمشابك‬ ‫الكیمیائیة‬ •The possible arrangements in typical neuron-to-neuron synapses are close junctions between the axon terminal of one neuron and the plasma membrane of another neuron . ‫الترتیب‬ ‫النموذجي‬ ‫للمشابك‬ ‫العصبیة‬ ‫للخالیا‬ ‫العصبیة‬ ‫هو‬ ‫االرتباط‬ ‫الوثیق‬ ‫بین‬ ‫نهایة‬ ‫محور‬ ‫عصبون‬ ‫لعصب‬ ‫واحد‬ ‫وغشاء‬ ‫البالزما‬ ‫لخلیة‬ ‫عصبون‬ ‫أخرى‬ . •The first neuron, which transmits signals to the second, is designated the presynaptic neuron ;the second neuron, which receives signals from the first, is referred to as the postsynaptic neuron . ‫ُطلق‬‫ی‬ ‫على‬ ‫العصبون‬ ‫األول‬ ‫الذي‬ ‫ینقل‬ ‫اإلشارات‬ ‫إلى‬ ‫العصبون‬ ‫الثاني‬ ‫اسم‬ ‫العصبون‬ ‫قبل‬ ‫المشبكي‬ ، ‫ویطلق‬ ‫على‬ ‫العصبون‬ ‫الثاني‬ ‫الذي‬ ‫یستقبل‬ ‫اإلشارات‬ ‫من‬ ‫العصبون‬ ‫األول‬ . ‫ُطلق‬‫ی‬ ‫على‬ ‫البطيء‬ ‫اسم‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •Most often the presynaptic neuron's axon terminal forms a synapse with either a dendrite or the cell body of the postsynapcic neuron, in which case the synapses are referred to as axodendritic or axosomatic synapses ,respectively. ‫في‬ ‫معظم‬ ‫الحاالت‬ ، ‫یشكل‬ ‫الجزء‬ ‫المحوري‬ ‫من‬ ‫العصبون‬ ‫قبل‬ ‫المشبكي‬ ‫ا‬ً‫ك‬‫مشاب‬ ‫مع‬ ‫جسم‬ ‫شجیري‬ ‫أو‬ ‫خلیة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ . ‫تسمى‬ ‫هذه‬ ‫األنواع‬ ‫من‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ ‫ا‬ ‫لمشابك‬ ‫العصبیة‬ ‫المحوریة‬ ‫والمشابك‬ ‫المحوریة‬ ، ‫على‬ ‫التوالي‬ . •In some cases the presynaptic neuron's axon terminal forms a synapse with the postsynaptic neuron's axon terminal, in which case the synapse is called an axoaxonic synapse ‫في‬ ‫بعض‬ ‫الحاالت‬ ، ‫یشكل‬ ‫ا‬ ‫لجزء‬ ‫المحوري‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ ‫ا‬ً‫ك‬‫مشاب‬ ‫مع‬ ‫طرف‬ ‫محور‬ ‫عصبي‬ ‫من‬ ‫العصبون‬ ‫قبل‬ ‫المشبكي‬ . ‫لهذا‬ ‫النوع‬ ‫من‬ ‫المشبك‬ ، ‫یطلق‬ ‫علیه‬ ‫المشبك‬ ‫المحوري‬ .
•In all cases, the axon terminal of the presynaptic neuron releases neurotransmitters into the narrow (30-50 nm) space between the two cells, called the synaptic cleft. ‫في‬ ‫جمیع‬ ‫الحاالت‬ ، ‫تضع‬ ‫المحطات‬ ‫المحوریة‬ ‫للخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكي‬ ‫نواقلها‬ ‫العصبیة‬ ‫في‬ ‫مساحة‬ ‫ضیقة‬ ( 09 ‫إلى‬ 59 ‫نانومتر‬ ) ‫بین‬ ‫خلیتین‬ ‫تسمى‬ - Synaptic ‫شق‬ ‫متشابك‬ ( ‫شق‬ ‫متشابك‬ ) . •Once released into the synaptic cleft, the neurotransmitters diffuse rapidly across the cleft and bind to receptors on the postsynaptic neuron ‫عندما‬ ‫یتم‬ ‫إطالق‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الفضاء‬ ‫المشبكي‬ ‫المشقوق‬ ، ‫فإنها‬ ‫تنتشر‬ ‫بسرعة‬ ‫عبر‬ ‫الشق‬ ‫وفي‬ ‫مستقبالتها‬ ‫المحددة‬ ‫على‬ ‫السطح‬ . ‫ترتبط‬ ‫الخالیا‬ ‫العصب‬ ‫یة‬ ‫بعد‬ ‫المشبكي‬ .
The binding of the neurotransmitter to the receptors produces a response in the postsynaptic neuron by a mechanism called signal transduction ‫ینتج‬ ‫ربط‬ ‫الناقالت‬ ‫العصبیة‬ ‫بالمستقبالت‬ ‫استجابة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫بو‬ ‫اسطة‬ ‫آلیة‬ ‫تسمى‬ ‫تحویل‬ ‫اإلشارة‬ . •The axon terminal of the presynaptic neuron contains numerous small, membrane-bound compartments called synaptic vesicles ,which store neurotransmitter molecules . ‫تحتوي‬ ‫المحطة‬ ‫المحوریة‬ ‫للخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكي‬ ‫على‬ ‫عدد‬ ‫ك‬ ‫بیر‬ ‫من‬ ‫الخالیا‬ ‫التي‬ ‫تحتوي‬ ‫على‬ ‫ناقالت‬ ‫عصبیة‬ ‫تسمى‬ ‫الحویصالت‬ ‫المشبكیة‬ . •Most neurotransmitters are synthesized in the cylosol of the axon terminal, where the enzymes for their synthesis are located. ‫تصنع‬ ‫معظم‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الخلیة‬ ‫الخلویة‬ ‫الطرفیة‬ ‫المحور‬ ‫یة‬ ( ‫حیث‬ ‫توجد‬ ‫اإلنزیمات‬ ‫الالزمة‬ ‫للقیام‬ ‫بذلك‬ ) . •After synthesis, neurotransmitters, are actively transported into synaptic vesicles, where they are stored until their eventual release by exocytosis.
‫بعد‬ ‫أن‬ ‫یتم‬ ‫تصنیعها‬ ، ‫یتم‬ ‫نقل‬ ‫النواقل‬ ‫الفارغة‬ ‫بنشاط‬ ‫إلى‬ ‫حوی‬ ‫صالت‬ ‫متشابكة‬ ‫وهناك‬ ‫حتى‬ ‫یتم‬ ‫إطالقها‬ ( ‫عن‬ ‫طریق‬ ‫اإلفراز‬ ‫الخلوي‬ ) . ‫یتم‬ ‫حفظها‬ .
Voltage-gated sodium and potassium channels are abundant in the membrane of the axon to support the propagation of action potentials down the length of the axon ‫توجد‬ ‫قنوات‬ ‫جه‬ ‫د‬ ‫الصودیوم‬ ‫والبوتاسیوم‬ ‫بكثرة‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫المحوار‬ ‫ویساعد‬ ‫عملها‬ ‫على‬ ‫نقل‬ ‫إمكانات‬ ‫العمل‬ ‫أثناء‬ ‫هو‬ ‫محور‬ ‫عصبي‬ . • But most abundant in the membrane of the axon terminal are voltage-gated calcium channels . ‫ولكن‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫الطرفیة‬ ‫المحوریة‬ ‫یوجد‬ ‫المزید‬ ‫من‬ ‫قنوات‬ ‫جهد‬ ‫الكالسیوم‬ . •These calcium channels open when the axon terminal is depolarized, which occurs upon arrival of an action potential at the axon terminal (see (1) in next Figure). ‫عندما‬ ‫یصل‬ ‫جهد‬ ‫الفعل‬ ‫إلى‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ( ‫ونهایة‬ ‫المحوار‬ ‫غیر‬ ‫مس‬ ‫تقطب‬ ) ، ‫تفتح‬ ‫قنوات‬ ‫الكالسیوم‬ ‫هذه‬ . •When the calcium channels open (2), they allow calcium to flow down its electrochemical gradient into the axon terminal, increasing the concentration of cytosolic calcium in the axon terminal. ‫عندما‬ ‫یتم‬ ‫فتح‬ ‫هذه‬ ‫القنوات‬ ، ‫یتدفق‬ ‫الكالسیوم‬ ‫إلى‬ ‫المحطة‬ ‫المحوریة‬ ً‫ء‬‫بنا‬ ‫على‬ ‫التدرج‬ ‫الكهروكیمیائي‬ ، ‫وتركیز‬ ‫الكالسیوم‬ ‫الخلوي‬ ‫في‬ ‫الطرف‬ ‫یزید‬ ‫المحور‬ ‫العصبي‬ .
•Calcium then causes the membranes of synaptic vesicles to fuse with vesicle attachment sites on the inner surface of the axon terminal membrane and undergo exocytosis, thereby releasing the neurotransmitters into the synaptic cleft (3). ‫یقوم‬ ‫الكالسیوم‬ ‫بعد‬ ‫ذلك‬ ‫بدمج‬ ‫أغشیة‬ ‫الحویصالت‬ ‫المشبكیة‬ ‫مع‬ ‫مواقع‬ ‫محددة‬ ‫على‬ ‫السطح‬ ‫الداخلي‬ ‫للغشاء‬ ‫الطرفي‬ ‫للمحور‬ ‫ویحدث‬ ‫خروج‬ ‫الخالیا‬ . ‫وهكذا‬ ، ‫یتم‬ ‫إطالق‬ ‫الن‬ ‫واقل‬ ‫العصبیة‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ . •Unless another action potential arrives, neurotransmitter release stops within a few milliseconds, because the voltage-gated calcium channels close soon after opening, and because calcium ions are actively transported out of the axon terminal on a continual basis, bringing the cytosolic calcium concentration back to its resting level. ‫إذا‬ ‫لم‬ ‫یتم‬ ‫الوصول‬ ‫إلى‬ ‫جهد‬ ‫فعل‬ ، ‫فإن‬ ‫إطالق‬ ‫النواقل‬ ‫العصبیة‬ ‫یتوقف‬ ‫في‬ ‫غضون‬ ‫بضعة‬ ‫أجزاء‬ ‫من‬ ‫األلف‬ ‫من‬ ‫الثانیة‬ ، ‫ألن‬ ‫قنوات‬ ‫الكالسیوم‬ ‫تغلق‬ ‫بسرعة‬ . ‫من‬ ‫ن‬ ‫احیة‬ ‫أخرى‬ ، ‫یتم‬ ‫نقل‬ ‫أیونات‬ ‫الكالسیوم‬ ‫بنشاط‬ ‫خارج‬ ‫المحطة‬ ‫المحوریة‬ ‫ویعود‬ ‫تركیز‬ ‫الكالسیوم‬ ‫في‬ ‫العصارة‬ ‫الخلویة‬ ‫إلى‬ ‫طبیعته‬ . ‫قبل‬ ‫العودة‬ . •A second action potential will elicit a quick burst of neurotransmitter release similar to the first. ‫تتسبب‬ ‫احتمالیة‬ ‫اإلجراء‬ ‫الثاني‬ ‫في‬ ‫اإلطالق‬ ‫المفاجئ‬ ‫للناقالت‬ ‫العصبیة‬ ‫كما‬ ‫كان‬ ‫من‬ ‫قبل‬ . •When a series of action potentials arrives at an axon terminal, the amount of neurotransmitter released from the presynaptic cell is greater than the amount released in response to a single action potential, and as a result the concentration of neurotransmitter in the synaptic cleft increases as the frequency of action potentials increases. ‫عندما‬ ‫تصل‬ ‫سلسلة‬ ‫من‬ ‫إمكانات‬ ‫الفعل‬ ‫إلى‬ ‫المحطة‬ ‫المحوریة‬ ، ‫فإن‬ ‫كمیة‬ ‫الناقالت‬ ‫العصبیة‬ ‫المنبعثة‬ ‫من‬ ‫الخالیا‬ ‫العصب‬ ‫یة‬ ‫قبل‬ ‫المشبكیة‬ ‫تكون‬ ‫أكبر‬ ‫من‬ ‫مجرد‬ ‫یصل‬ ‫إلى‬ ‫جهد‬ ‫فعل‬ ‫واحد‬ ، ‫وبالتالي‬ ‫فإن‬ ‫زیادة‬ ‫تواتر‬ ‫جهد‬ ‫الفعل‬ ‫یزید‬ ‫من‬ ‫تركیز‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ .
•Once in the synaptic cleft, neurotransmitter molecules diffuse away from the axon terminal and toward the postsynaptic neuron, where they bind to receptors (see (4) in next figure), thereby inducing a response in the postsynaptic neuron (5) ‫ثم‬ ‫تنتشر‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫وترتبط‬ ‫بمستقبالتها‬ ‫المحددة‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫تكوین‬ ‫الردود‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •The binding of a neurotransmitter molecule to a receptor is a brief and reversible process. ‫یكون‬ ‫اتصال‬ ‫الناقل‬ ‫العصبي‬ ‫بالمستقبل‬ ‫ًا‬‫ی‬‫مقطع‬ ً ‫وقابال‬ ‫لالنعكاس‬ . The neurotransmitter is a ligand and the receptor is a protein, and the two bind through weak chemical interactions ‫الناقل‬ ‫العصبي‬ ‫عبارة‬ ‫عن‬ ‫لیجند‬ ‫والمستقبالت‬ ‫عبارة‬ ‫عن‬ ‫بروتین‬ ، ‫وكالهما‬ ‫یرتبط‬ ‫ببعضهما‬ ‫البعض‬ ‫بروابط‬ ‫كیمیائیة‬ ‫ضعیفة‬ . •If neurotransmitter molecules were to remain indefinitely in the synaptic cleft following their release, they would bind to receptors over and over again, inducing a continual response in the postsynaptic neuron.
‫إذا‬ ‫كانت‬ ‫النواقل‬ ‫العصبیة‬ ‫مرتبطة‬ ‫بشكل‬ ‫دائم‬ ‫ومستمر‬ ‫بالمستقبالت‬ ، ‫فإنها‬ ‫ستثیر‬ ‫استجابة‬ ‫دائمة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ . •However, continual binding does not occur because a number of processes quickly clear the neurotransmitter from the cleft, thereby terminating the signal. ‫ومع‬ ‫ذلك‬ ، ‫ال‬ ‫یحدث‬ ‫هذا‬ ( ‫االتصال‬ ‫الدائم‬ ‫للناقل‬ ‫العصبي‬ ‫بالمستقبالت‬ ) ‫ألن‬ ‫العدید‬ ‫من‬ ‫العملیات‬ ‫تتسبب‬ ‫في‬ ‫إزالة‬ ‫الناقل‬ ‫العصبي‬ ‫بسرعة‬ ‫من‬ ‫الشق‬ ‫المشبكي‬ . •Some neurotransmitter molecules are degraded by enzymes ,which may be located either on the postsynaptic neuron's plasma membrane (see (6) in next figure), on the presynaptic neuron's plasma membrane, on the plasma membranes of nearby glial cells, or even in the cytoplasm of the presynaptic neuron or glial cells . ‫یتم‬ ‫إنتاج‬ ‫بعض‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫بواسطة‬ ‫اإلنزیمات‬ ‫الموجودة‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ ، ‫أو‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ، ‫أو‬ ‫الخالیا‬ ‫الدبقیة‬ ، ‫أو‬ ‫حتى‬ ‫ینهار‬ ‫سیتوبالزم‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكي‬ ‫أو‬ ‫الخالیا‬ ‫الدبقیة‬ . •Other neurotransmitter molecules can be actively transported back into the presynaptic neuron that released them (see (7) in next figure), a process known as reuptake . ‫یتم‬ ‫إرجاع‬ ‫بقیة‬ ‫جزیئا‬ ‫ت‬ ‫الناقل‬ ‫العصبي‬ ‫بنشاط‬ ‫إلى‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ ( ‫آلیة‬ ‫تسمى‬ ‫االسترداد‬ ) . •Once inside the neuron, these neurotransmitter molecules are usually degraded and the breakdown products recycled to form new neurotransmitter molecules . ‫تتحلل‬ ‫النواقل‬ ‫العصب‬ ‫یة‬ ‫بعد‬ ‫دخولها‬ ‫الخلیة‬ ‫وتستخدم‬ ‫نواتج‬ ‫التحلل‬ ‫لصنع‬ ‫جزیئات‬ ‫ناقل‬ ‫عصبي‬ ‫جدیدة‬ . ‫تم‬ ‫وضعه‬ . •Other neurotransmitter molecules in the synaptic cleft simply diffuse out of the cleft (see (8) in next figure) ‫یتم‬ ‫تحریر‬ ‫جزء‬ ‫آخر‬ ‫من‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ ‫عن‬ ‫ط‬ ‫ریق‬ ‫االنتشار‬ ‫البسیط‬ . •So long as neurotransmitter molecules are not bound to receptors, they may be subject to any of the fates just described.
‫تواجه‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫غیر‬ ‫المرتبطة‬ ‫بالمستقبالت‬ ‫أحد‬ ‫المصائر‬ ‫المذكورة‬ ‫أعاله‬ . •As a result, neurotransmitter is usually present in the synaptic cleft for only a few milliseconds after its release from the presynaptic neuron. ‫نتیجة‬ ‫لذلك‬ ، ‫تبقى‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ ‫لبضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ ‫بعد‬ ‫إطالقها‬ . •It takes approximately 1-5 msec from the time an action potential arrives at the axon terminal before a response occurs in the postsynaptic cell ‫یحدث‬ ‫إطالق‬ ‫النواقل‬ ‫العصبیة‬ ‫من‬ 2 ‫إلى‬ 5 ‫أجزاء‬ ‫من‬ ‫الثانیة‬ ‫بعد‬ ‫وصول‬ ‫جهد‬ ‫الفعل‬ ‫إلى‬ ‫المحطة‬ ‫المحوریة‬ . •This time lag, called the synaptic delay, is mostly due to the time required for calcium to trigger the exocytosis of neurotransmitter. ‫یسمى‬ ‫وقت‬ ‫التأخیر‬ ‫هذا‬ ‫بالتأخیر‬ ‫المشبكي‬ ‫ویرجع‬ ‫ذلك‬ ‫إلى‬ ‫الوقت‬ ‫الالزم‬ ‫لعمل‬ ‫الكالسیوم‬ ‫لبدء‬ ‫إفراز‬ ‫الناقل‬ ‫العصبي‬ . •Once in the synaptic cleft, diffusion of neurotransmitter to the receptor is so rapid as to be negligible. ‫في‬ ‫الشق‬ ‫المشبكي‬ ، ‫ینتشر‬ ‫الناقل‬ ‫العصبي‬ ‫ویرتبط‬ ‫بالمستقبل‬ ‫بسرعة‬ ‫كبیرة‬ ، ‫والوقت‬ ‫الالزم‬ ‫للقیام‬ ‫بذلك‬ ‫ال‬ ‫یكاد‬ ‫یذكر‬ . •Norepinephrine is actively transported back to the pre-synaptic axon ‫یتم‬ ‫نقل‬ ‫النواقل‬ ‫العصبیة‬ ‫مثل‬ norepinephrine ‫بنشاط‬ ‫إلى‬ ‫محور‬ ‫عصبي‬ ‫قبل‬ ‫المشبكي‬ . •CNS neurotransmitters (amines, peptides, amino acids) move into circulation or transported to pre- synaptic terminal. ‫تتدفق‬ ‫الناقالت‬ ‫العصبیة‬ ‫للجهاز‬ ‫العصبي‬ ‫المركزي‬ ( ‫األمینات‬ ‫والببتیدات‬ ‫واألحماض‬ ‫األمینیة‬ ) ‫إلى‬ ‫مجرى‬ ‫الدم‬ ‫أو‬ ‫تنتقل‬ ‫إلى‬ ‫الخلیة‬ ‫قبل‬ ‫المشبكیة‬ .
Signal Transduction Mechanisms at Chemical Synapses ‫آلیات‬ ‫إرسال‬ ‫اإلشارات‬ ‫في‬ ‫المشابك‬ ‫الكیمیائیة‬ •The neurotransmitter released by a presynaptic neuron is a messenger ‫الناقل‬ ‫العصبي‬ ‫المنطلق‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبك‬ ‫یة‬ ‫لنبي‬ . •When it binds to receptors on the postsynaptic neuron, a message is conveyed. ‫عندما‬ ‫یرتبط‬ ‫هذا‬ ‫الناقل‬ ‫العصبي‬ ‫بمستقبالته‬ ‫في‬ ‫العصبون‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫تنتقل‬ ‫الرسالة‬ ‫ًا‬‫ی‬‫فعل‬ . •Neurotransmitters can induce in a postsynaptic neuron either a fast or a slow response. ‫یمكن‬ ‫أن‬ ‫تحفز‬ ‫الناقالت‬ ‫العصبیة‬ ‫استجابات‬ ‫سریعة‬ ‫أو‬ ‫بطیئة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . Fast response ‫استجابة‬ ‫حادة‬ •Fast response occurs whenever a neurutransmitter binds to a channel-linked receptor ,also called an ionotropic receptor. ‫تحدث‬ ‫اال‬ ‫ستجابة‬ ‫السریعة‬ ‫عندما‬ ‫یتصل‬ ‫ناقل‬ ‫عصبي‬ ‫بمستقبل‬ ‫متصل‬ ‫بالقناة‬ ‫أو‬ ‫مستقبل‬ ‫مؤثر‬ ‫في‬ ‫األیونات‬ . •All channel-linked receptors are ligand-gated channels . ‫جمیع‬ ‫المستقبالت‬ ‫المتصلة‬ ‫بالقناة‬ ‫هي‬ ‫قنوات‬ ‫یجند‬ .
•The binding of the neurotransmitter opens the ion channel, allowing a specific ion or ions to permeate the plasma membrane and change the electrical properties of the postsynaptic neuron . ‫یؤدي‬ ‫ارتباط‬ ‫ناقل‬ ‫عصبي‬ ‫إلى‬ ‫فتح‬ ‫القناة‬ ‫األیونیة‬ ‫واختراق‬ ‫أیونات‬ ‫أو‬ ‫أیونات‬ ‫معینة‬ ‫من‬ ‫غشاء‬ ‫البالزما‬ ‫وتغیرات‬ ‫في‬ ‫الخواص‬ ‫الكهربائیة‬ ‫لما‬ ‫بعد‬ ‫یصبح‬ ‫متشابك‬ •The typical response is a change in the membrane potential, called a postsynaptic potential ,or PSP ,which occurs very rapidly and turns off rapidly (normally within a lew milliseconds) because the channel closes as soon as the neuroiransmitter leaves the receptor. ‫تتمثل‬ ‫االستجابة‬ ‫المعتادة‬ ‫في‬ ‫هذه‬ ‫الحالة‬ ‫في‬ ‫إجراء‬ ‫تغییر‬ ‫في‬ ‫إمكانات‬ ‫الغشاء‬ ‫تسمى‬ ‫إمكانات‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫أو‬ PSP ، ‫وهي‬ ‫سریعة‬ ‫ًا‬‫د‬‫ج‬ ‫وشدیدة‬ ‫التحمل‬ . ‫یختفي‬ ‫بسرعة‬ ( ‫في‬ ‫بضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ ) ‫ألن‬ ‫القناة‬ ‫تغلق‬ ‫بسرعة‬ ‫بعد‬ ‫أن‬ ‫ینفصل‬ ‫الناقل‬ ‫العصبي‬ ‫عن‬ ‫المستقبل‬ . Slow responses ‫رد‬ ‫بطيء‬ •Slow responses, on the other hand, are mediated through G-protein-linked receptors called metabotropic receptors ,which include any receptor that works by triggering biochemical changes rather than simply inducing a change in permeability
‫یتم‬ ‫التوسط‬ ‫في‬ ‫االستجابات‬ ‫البطیئة‬ ‫بواسطة‬ ‫مستقبالت‬ ‫البروتین‬ G ( ‫وتسمى‬ ‫ًا‬‫ض‬‫أی‬ ‫مستقبالت‬ ‫التمثیل‬ ‫الغذائي‬ ) ‫تعمل‬ ‫التغییرات‬ ‫البیوكیمیائیة‬ ، ‫ولیس‬ ‫التغییرات‬ ‫البسیطة‬ ‫في‬ ‫نفاذیة‬ ‫الغشاء‬ . •In the nervous system, G proteins can trigger either the opening or the closing of ion channels, depending on the specific synapse . ‫في‬ ‫الجهاز‬ ‫العصبي‬ ، ‫یمكن‬ ‫أن‬ ‫تتسبب‬ ‫بروتینات‬ G ‫في‬ ‫فتح‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ، ‫ًا‬‫د‬‫اعتما‬ ‫على‬ ‫نوع‬ ‫المشبك‬ •These G-protein-regulated ion channels respond to the binding of neurotransmitter more slowly than the channels that mediate the fast response, with durations ranging from milliseconds to hours, depending on the synapse, but with the same ultimate effect : ‫قنوات‬ Y ‫األیونیة‬ ‫التي‬ ‫یتحكم‬ ‫فیها‬ ‫بروتین‬ G ‫أبطأ‬ ‫بكثیر‬ ‫في‬ ‫االرتباط‬ ‫بالناقالت‬ ‫العصبیة‬ ‫من‬ ‫قنوات‬ ‫االستجابة‬ ‫السریعة‬ . ‫أظهر‬ ‫أنه‬ ‫یمكن‬ ‫أن‬ ‫یكون‬ ‫من‬ ‫بضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ ‫إلى‬ ‫بضع‬ ‫ساعات‬ ( ‫حسب‬ ‫نوع‬ ‫المشبك‬ ) ‫لكن‬ ‫تأثیراتها‬ ‫متشابهة‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ : •1-The opening or closing of ion channels alters the permeability of the postsynaptic neuron to a specific ion or ions, resulting in changes in the electrical properties of the cell. •2-The G protein can serve as a direct coupling between the receptor and the ion channel (figure b), or it can trigger the activation or inhibition of a second messenger system (figure c) •3-Neurotransmitters that act through G proteins are also called neuromodulators because some of the slow responses modulate the fast responses occurring at ionotropic receptors. 2. ‫یؤدي‬ ‫فتح‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ‫إلى‬ ‫تغییر‬ ‫في‬ ‫نفاذیة‬ ‫الخالیا‬ ‫ا‬ ‫لعصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫إلى‬ ‫أیونات‬ ‫أو‬ ‫أیونات‬ ‫محددة‬ ، ‫وبالتالي‬ ‫تغیرات‬ ‫في‬ ‫الخصائص‬ ‫تصبح‬ ‫الخلیة‬ ‫كهربائیة‬ . 2. ‫یعمل‬ ‫البروتین‬ G ‫كرابط‬ ‫مباشر‬ ‫بین‬ ‫المستقبل‬ ‫والقناة‬ ‫األیونیة‬ ‫أو‬ ‫یمكنه‬ ‫تنشیط‬ ‫أو‬ ‫تثبیط‬ ‫نظام‬ ‫المرسل‬ ‫الثانوي‬ . ‫عرف‬ُ‫ت‬ ‫الناقالت‬ ‫العصبیة‬ ‫التي‬ ‫تعمل‬ ‫من‬ ‫خالل‬ ‫بروتینات‬ G ‫ًا‬‫ض‬‫أی‬ ‫باسم‬ ‫ِّالت‬‫عد‬ُ‫م‬‫ال‬ ‫العصبیة‬ ‫ألن‬ ‫بعض‬ ‫االستجابات‬ ‫البطیئة‬ ‫تعدل‬ ‫االستجابة‬ . ‫تتولد‬ ‫بسرعة‬ ‫في‬ ‫مستقبالت‬ ‫التأین‬ .
Excitatory and inhibitory Synapses ‫المشابك‬ ‫التحفیزیة‬ ‫والمثبطة‬ •In general, a neurotransmitter exerts its effects on a postsynaptic neuron by triggering the opening or closing of ion channels, which typically causes a change in membrane potential.
‫تمارس‬ ‫الناقالت‬ ‫العصبیة‬ ‫ا‬ً‫م‬‫عمو‬ ‫تأثیرها‬ ‫على‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫عن‬ ‫طریق‬ ‫تحفیز‬ ‫فتح‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ‫التي‬ ‫تغیر‬ ‫إمكانات‬ ‫الغشاء‬ . ‫تطبیق‬ . •Depending on the type of channel that is opened or closed, the resulting change in membrane potential may be positive or negative ;that is, it may cause either a depolarization or a hyperpolarization ,respectively. ‫ًا‬‫د‬‫اعتما‬ ‫على‬ ‫نوع‬ ‫القناة‬ ‫التي‬ ‫تفتح‬ ‫أو‬ ‫غل‬ُ‫ت‬ ‫ق‬ ، ‫قد‬ ‫یكون‬ ‫التغییر‬ ‫في‬ ‫إمكانات‬ ‫الغشاء‬ ‫ًا‬‫ی‬‫إیجاب‬ ‫أو‬ ‫ًا‬‫ی‬‫سلب‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫إزالة‬ ‫االستقطاب‬ ، ‫أو‬ ‫یصبح‬ ‫مفرط‬ ‫االستقطاب‬ . •At any given synapse, the direction of the response is always the same, and the synapse is classified as being either excitatory and inhibitory synapses ‫في‬ ‫المشبك‬ ، ‫یكون‬ ‫اتجاه‬ ‫االستجابة‬ ‫هو‬ ‫نفسه‬ ‫ا‬ً‫م‬‫دائ‬ ، ‫وینقسم‬ ‫المشبك‬ ‫إلى‬ ‫مثیر‬ ‫ومثبط‬ . Excitatory Synapses ‫تحفیز‬ ‫السینابیس‬ •An excitatory synapse is one that brings the membrane potential of the postsynaptic neuron closer to the threshold for generating an action potential; that is, excitatory synapses depolarize the postsynaptic neuron. ‫یخلق‬ ‫المشبك‬ ‫االستثاري‬ ‫إمكانات‬ ‫فعلیة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ‫ویزیل‬ ‫استقطاب‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •This depolarization is called an excitatory postsynaptic potential, or EPSP, and can occur as either a fast response or a slow response. ‫یسمى‬ ‫هذا‬ ‫االستقطاب‬ ‫بالجهد‬ ‫المثیر‬ ‫لما‬ ‫بعد‬ ‫المشبكي‬ ، ‫أو‬ EPSP ، ‫ویمكن‬ ‫أن‬ ‫یحدث‬ ‫في‬ ‫شكل‬ ‫استجابة‬ ‫بطیئة‬ ‫أو‬ ‫سریعة‬ . Fast EPSPs ‫شارب‬ EPSPs •Fast EPSPs are generally caused by the binding of neurotransmitter molecules to their receptors on the postsynaptic cell, in the process opening channels that allow small cations (sodium and potassium ions) to move through them (Figure a) ً‫ة‬‫عاد‬ ‫ما‬ ‫یكون‬ ‫سبب‬ ‫التهاب‬ ‫العصب‬ ‫البصري‬ ‫الحاد‬ ‫هو‬ ‫ارتباط‬ ‫جزی‬ ‫ئات‬ ‫الناقل‬ ‫العصبي‬ ‫بمستقبالتها‬ ‫المحددة‬ ‫في‬ ‫الخلیة‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ‫وفتح‬ ‫القنوات‬ ‫التي‬ ‫تسمح‬ ‫یحدث‬ ‫االنتقال‬ ‫إلى‬ ‫الكاتیونات‬ ‫الصغیرة‬ (Na ‫و‬ K)
•Recall that at resting potential ,sodium is far from equilibrium, and that there is a strong electrochemical force for moving sodium ions into the cell ,whereas because potassium is near equilibrium, only a weak electrochemical force exists for moving potassium ions out of the cell . ‫من‬ ‫المفترض‬ ‫أنه‬ ‫في‬ ‫حالة‬ ‫الراحة‬ ، ‫یكون‬ ‫الصودیوم‬ ‫في‬ ‫حالة‬ ‫عدم‬ ‫توازن‬ ‫ولدیه‬ ‫میل‬ ‫كهروكیمیائي‬ ‫مرتفع‬ ‫ل‬ ‫دخول‬ ‫الخلیة‬ ، ‫بینما‬ ‫البوتاسیوم‬ ‫قریب‬ ‫من‬ ‫التوازن‬ ‫وهناك‬ ‫القلیل‬ ‫من‬ ‫المیل‬ ‫الكهروكیمیائي‬ ‫لمغادرة‬ ‫الخلیة‬ . •Therefore, when channels open, allowing both sodium and potassium ions to move through them, more sodium ions move in than potassium ions move out, producing a net depolarization. ‫لذلك‬ ، ‫عند‬ ‫فتح‬ ‫القنوات‬ ، ‫ُسمح‬‫ی‬ ‫ألیونات‬ K ‫و‬ Na ‫بالمرور‬ ‫عبرها‬ ‫ویدخل‬ ‫المزید‬ ‫من‬ ‫الصودیوم‬ ‫إلى‬ ‫الخلیة‬ ‫بینما‬ ‫أقل‬ ‫من‬ K ‫یترك‬ ‫الخلیة‬ ‫وهذا‬ ‫یسبب‬ ‫نزع‬ ‫االستقطاب‬ . •Note on the voltmeter (oscilloscope) in next Figure that fast EPSPs last only milliseconds. ‫الحظ‬ ‫مقیاس‬ ‫الفولتمیتر‬ ( ‫راسم‬ ‫الذبذبات‬ ) ‫في‬ ‫الشكل‬ ‫أ‬ ‫؛‬ ‫تدوم‬ ESPS ‫السریع‬ ‫فقط‬ ‫بضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ .
Slow EPSPs EPSPs ‫بطیئة‬ •Slow EPSPs can be caused by various mechanisms, but a typical mechanism is the closing of potassium channels involving the most common second messenger, cAMP (Figure b) ‫یتم‬ ‫إنتاج‬ EPSPs ‫البطيء‬ ‫بواسطة‬ ‫مجموعة‬ ‫متنوعة‬ ‫من‬ ‫اآللیات‬ ، ‫ولكن‬ ‫اآللیة‬ ‫األكثر‬ ‫ًا‬‫ع‬‫شیو‬ ‫ترجع‬ ‫إلى‬ ‫إغالق‬ ‫قنوات‬ ‫البوتاسیوم‬ ‫بواسطة‬ cAMP ‫المرسال‬ ‫الثانوي‬ . •When the neurotransmittcr binds to a receptor (1) and activates a G protein (2), the G protein then activates the enzyme adenylate cyclasc(3), which then catalyzes the reaction converting ATP to cAMP (4). ‫عندما‬ ‫یتصل‬ ‫ناقل‬ ‫عصبي‬ ‫بالمستقبل‬ ( 2 ) ‫وینشط‬ ‫بروتین‬ G (2) ، ‫ینشط‬ ‫بروتین‬ G ‫إنزیم‬ ‫دورة‬ adenylate 0) ‫وهذا‬ ‫اإلنزیم‬ ‫یحول‬ ATP ‫إلى‬ cAMP) 4) • cAMP acts as a second messenger that activates protein kinase A (5), which catalyzes the addition of a phosphate group to the potassium channel (6). Phosphorylation of the potassium channel closes it (7) cAMP ‫كمرسل‬ ‫ثانوي‬ ‫ینشط‬ ‫بروتین‬ ‫كینا‬ ‫ز‬ ‫أ‬ ( 5 ) ‫الذي‬ ‫یضیف‬ ‫مجموعة‬ ‫فوسفات‬ ‫إلى‬ ‫قناة‬ ‫البوتاسیوم‬ (6) ‫تؤدي‬ ‫الفسفرة‬ ‫في‬ ‫قناة‬ ‫البوتاسیوم‬ ‫إلى‬ ‫إغالقها‬ ) 0 . •Before the potassium channel was phosphorylaled, the channel was open, and potassium ions were leaking out of the cell while sodium ions were leaking into the cell. ‫قبل‬ ‫فسفرة‬ ‫قناة‬ ‫البوتاسیوم‬ ، ‫تكون‬ ‫هذه‬ ‫القناة‬ ‫مفتوحة‬ ، ‫مما‬ ‫یتسبب‬ ‫في‬ ‫تسرب‬ ‫أیونات‬ K ‫ودخول‬ Na ‫إلى‬ ‫الخلیة‬ •No change in membrane potential was occurring because the sodium and potassium leaks were balanced. ‫في‬ ‫هذه‬ ‫الحالة‬ ، ‫ال‬ ‫تتغیر‬ ‫إمكانات‬ ‫الغشاء‬ ‫ألن‬ ‫تسرب‬ K ‫و‬ Na ‫في‬ ‫حالة‬ ‫توازن‬ . • ‫عندما‬ ‫یتم‬ ‫إغالق‬ ‫قناة‬ ‫البوتاسیوم‬ ‫عن‬ ‫طریق‬ ‫الفسفرة‬ ، ‫یتسرب‬ ‫عدد‬ ‫أقل‬ ‫من‬ ‫أیونات‬ ‫البوتاسیوم‬ ‫من‬ ‫الخلیة‬ •The net effect is a depolarization, because if permeability to potassium decreases while permeability to sodium remains the same, the membrane potential will move away from the equilibrium potential for potassium and toward the equilibrium potential for sodium .
‫التأثیر‬ ‫الصافي‬ ‫لهذا‬ ‫هو‬ ‫إزالة‬ ‫االستقطاب‬ ، ‫ألنه‬ ‫عندما‬ ‫تنخفض‬ ‫نفاذیة‬ ‫البوتاسیوم‬ ‫بینما‬ ‫ال‬ ‫تتغیر‬ ‫نفاذیة‬ ‫الصودیوم‬ ، ‫فإن‬ ‫اإلمك‬ ‫انات‬ ‫الغشاء‬ ‫خارج‬ ‫التوازن‬ ‫لـ‬ K ‫ویتحرك‬ ‫نحو‬ ‫توازن‬ ‫الصودیوم‬ •Slow EPSPs take longer to develop and last longer (seconds lo hours) than fast EPSPs. In the case of cAMPdependent closure of potassium channels, the membrane potential will not return to resting conditions until the potassium channels are dephosphorylated, which will not occur until enough cAMP has been degraded by phosphodiesterase to return the cAMP concentration to its resting level. ‫مدة‬ EPSPs ‫بطیئة‬ ‫وطویلة‬ ‫وطویلة‬ ‫األمد‬ ‫ًا‬‫ض‬‫أی‬ ‫طویلة‬ ( ‫بضع‬ ‫ثوان‬ ‫إل‬ ‫ى‬ ‫بضع‬ ‫ساعات‬ ) ، ‫بینما‬ ‫قنوات‬ ‫البوتاسیوم‬ ‫مع‬ ‫یتم‬ ‫إغالق‬ ‫اآللیة‬ ‫المعتمدة‬ ‫على‬ cAMP ، ‫وال‬ ‫تعود‬ ‫إمكانات‬ ‫الغشاء‬ ‫إلى‬ ‫الراحة‬ ‫ما‬ ‫لم‬ ‫یتم‬ ‫إعادة‬ ‫فسفرة‬ ‫قنوات‬ ‫البوتاسیوم‬ ، ‫وهذا‬ ‫یحدث‬ ‫هذا‬ ‫اإلجراء‬ ‫عندما‬ ‫یتحلل‬ cAMP ‫بواسطة‬ ‫إنزیم‬ phosphordiasterase
‫المشابك‬ ‫المثبطة‬ •An inhibitory synapse is one that either takes the membrane potential of the postsynaptic neuron away from the action potential threshold by hyperpolarizing the neuron ,or stabilizes the membrane potential at the resting value . ‫المشبك‬ ‫المثبط‬ ‫هو‬ ‫المشبك‬ ‫الذي‬ ‫یتم‬ ‫منعه‬ ‫عن‬ ‫طریق‬ ‫فرط‬ ‫االستقطاب‬ ‫أو‬ ‫عن‬ ‫طریق‬ ‫الحفاظ‬ ‫على‬ ‫إمكانات‬ ‫عمل‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫ثابتة‬ ‫في‬ ‫حالة‬ ‫الراحة‬ . ‫یصبح‬ ‫جهد‬ ‫الفعل‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •In either case, activity at the synapse decreases the likelihood that an action potential will be generated in the postsynaptic nenron (which is why the synapse is said to be inhibitory). ‫في‬ ‫كلتا‬ ‫الحالتین‬ ، ‫یقلل‬ ‫نشاط‬ ‫هذا‬ ‫المشبك‬ ‫من‬ ‫احتمالیة‬ ‫الفعل‬ ‫المحتمل‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •At inhibitory synapses, the binding of a neurotransmitter to its receptors opens channels for either potassium ions or chloride ions. ‫في‬ ‫المشبك‬ ‫المثبط‬ ، ‫یؤدي‬ ‫ارتباط‬ ‫الناقل‬ ‫العصبي‬ ‫بالمستقبالت‬ ‫إلى‬ ‫فتح‬ ‫قنوات‬ ‫ألیونات‬ ‫الكلور‬ ‫والبوتاسیوم‬ . •When a neurotransrnitter causes potassium channels to open, potassium will move out of the cell, hyperpolarizing it . ‫عندما‬ ‫یتسبب‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫فتح‬ ‫القنوات‬ ، ‫یتم‬ ‫إطالق‬ ‫البوتاسیوم‬ ‫من‬ ‫الخلیة‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫فرط‬ ‫استقطاب‬ ‫الخلیة‬ . •This hyperpolarization is called an inhibitory post-synaptic potential ,orIPSP .
‫یسمى‬ ‫هذا‬ ‫االستقطاب‬ ‫المفرط‬ ‫بإمكا‬ ‫نیة‬ ‫تثبیط‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫أو‬ IPSP •An IPSP, like an EPSP, is a graded potential: When more neurotransmitter molecules bind to receptors, more potassium channels open and the hyperpolarization is greater. ‫یتمتع‬ IPSP ، ‫مثل‬ EPSP ، ‫بإمكانیة‬ ‫متدرجة‬ : ‫كلما‬ ‫زاد‬ ‫ارتباط‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫بالمستقبالت‬ ، ‫زادت‬ ‫القنوا‬ ‫یتم‬ ‫إطالق‬ ‫المزید‬ ‫من‬ ‫البوتاسیوم‬ ‫وسیكون‬ ‫فرط‬ ‫االستقطاب‬ ‫أكثر‬ ‫حدة‬ (‫مثل‬ EPSP) • IPSPs (like EPSPs and all other graded potentials) decrease in size as they move toward the axon hillock, where the hyperpolarization moves the membrane potential away from threshold, thereby decreasing the likelihood that an action potential will be generated in the postsynaptic neuron. ‫بینما‬ ‫نتحرك‬ ‫على‬ ‫طول‬ ‫المحور‬ ‫العصبي‬ ‫إلى‬ ‫سلسلة‬ ‫التالل‬ ‫المحوریة‬ (‫محور‬ hillock axon) ، ‫تنخفض‬ ‫كمیة‬ IPSPs (‫مثل‬ EPSPs)
Inhibitory post-synaptic potential involving potassium channels ‫في‬ IPSP ، ‫تشارك‬ ‫قنوات‬ ‫البوتاسیوم‬ •What happens when a neurotransmitter causes chloride (Cl- ) channels to open depends on the size and direction of the electrochemical driving force acting to move chloride ions across the postsynaptic neuron membrane. ‫عندما‬ ‫یتسبب‬ ‫ناقل‬ ‫عصبي‬ ‫في‬ ‫فتح‬ ‫قنوات‬ ‫الكلور‬ ( ‫حسب‬ ‫حجم‬ ‫واتجاه‬ ‫قوة‬ ‫التوصیل‬ ) ‫وعبور‬ ‫أیونات‬ ‫الكلور‬ ‫الغشاء‬ ‫بعد‬ ‫المشبكي‬ ‫تصبح‬ ‫خالیا‬ ‫عصبیة‬ ، ‫ما‬ ‫یحدث‬ . •Because the chloride ion has a negative charge (is an anion), the membrane potential at rest is an electrical force that acts to move chloride out of the cell . ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫أیونات‬ ‫الكلور‬ ‫لها‬ ‫شحنة‬ ‫سالبة‬ ، ‫فإن‬ ‫إمكانات‬ ‫الغشاء‬ ‫في‬ ‫حالة‬ ‫السكون‬ ‫تسبب‬ ‫قوة‬ ‫كهربائیة‬ ‫تمیل‬ ‫إلى‬ ‫طرد‬ ‫أیونات‬ ‫الكلور‬ . ‫من‬ ‫الخلیة‬ ‫یمكن‬ ‫أن‬ ‫یكون‬ •However, because chloride ions are found in greater concentration outside the cell than inside, there is a chemical force for moving chloride into the cell . ‫ومع‬ ‫ذلك‬ ، ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫تركیز‬ ‫أیونات‬ ‫الكلور‬ ‫خارج‬ ‫الخلیة‬ ‫أعلى‬ ‫منه‬ ‫بداخلها‬ ، ‫فهنا‬ ‫ك‬ ‫ًا‬‫ض‬‫أی‬ ‫قوة‬ ‫كیمیائیة‬ ‫لدخول‬ ‫الكلور‬ ‫إلى‬ ‫الخلیة‬ . •The net force depends on the neuron in question. ‫لها‬ ‫قوى‬ ‫نقیة‬ ‫تعتمد‬ ‫على‬ ‫حالة‬ ‫الخالیا‬ ‫العصبیة‬ . • In some neurons, chloride ions are actively transported out of the cell, making the concentration outside much higher than inside the cell. ‫في‬ ‫بعض‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫یتم‬ ‫طرد‬ ‫أیونات‬ ‫الكلور‬ ‫بشكل‬ ‫نشط‬ ‫من‬ ‫الخلیة‬ ، ‫وبالتالي‬ ‫یكون‬ ‫تركیز‬ ‫الكلور‬ ‫خارج‬ ‫الخلیة‬ ‫أعلى‬ ‫بكثیر‬ ‫منه‬ ‫داخل‬ ‫الخلیة‬ . • Under these conditions, the equilibrium potential for chloride is negative and larger than the resting membrane potential. ‫في‬ ‫مثل‬ ‫هذه‬ ‫الحالة‬ ، ‫تكون‬ ‫احتمالیة‬ ‫توازن‬ ‫الكلور‬ ‫سالبة‬ ‫وهي‬ ‫أكبر‬ ‫من‬ ‫احتمالیة‬ ‫الراحة‬ ‫للغشاء‬ . •In other neurons no active transport of chloride occurs, but there are some ion channels through which chloride can diffuse. ‫في‬ ‫بعض‬ ‫ال‬ ‫خالیا‬ ‫العصبیة‬ ‫األخرى‬ ، ‫ال‬ ‫یوجد‬ ‫نقل‬ ‫نشط‬ ‫للكلور‬ ‫وهناك‬ ‫قنوات‬ ‫إلطالق‬ ‫الكلور‬ .
عصبی11
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عصبی11

  • 1. Nervous system ‫الجهاز‬ ‫العصبي‬ •The nervous system can be divided into two main anatomical parts: the central nervous system (CNS) and the peripheral nervous system (PNS) ‫مرکزی‬ ‫عصبی‬ ‫سیستم‬ :‫میشود‬ ‫تقسیم‬ ‫اصلی‬ ‫بخش‬ ‫دو‬ ‫به‬ ‫آناتومیکی‬ ‫نظر‬ ‫از‬ ‫عصبی‬ ‫سیستم‬ ) CNS ) ‫سیستم‬ ‫و‬ ‫محیطی‬ ‫عصبی‬ )PNS) •The central nervous system consists of the brain and spinal cord. ‫یشمل‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫الدماغ‬ ‫والنخاع‬ ‫الشوكي‬ . •It (CNS) receives and processes information from the organs and then sends information back to the organs, instructing them to perform various tasks . ‫یتلقى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫المعلومات‬ ‫من‬ ‫األعضاء‬ ‫ویعالجها‬ ‫ثم‬ ‫یعید‬ ‫المعلومات‬ ‫المعالجة‬ ‫إلى‬ ‫األعضاء‬ ‫ویأمر‬ ‫باإلجراءات‬ ‫التي‬ ‫یتعین‬ ‫القیام‬ ‫بها‬ . ‫یعطي‬ ‫األطراف‬ ‫أجزاء‬ ‫مختلفة‬ . •The central nervous system is also the site of learning ,memory, emotions, and other complex functions. ‫یعد‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫ًا‬‫ض‬‫أی‬ ‫المكان‬ ‫المناسب‬ ‫للقیام‬ ‫بأشیاء‬ ‫مثل‬ ‫التعلم‬ ‫والذاكرة‬ ‫والعواطف‬ ‫والوظائف‬ ‫المعقدة‬ ‫األخرى‬ . •The peripheral nervous system consists of nerve cells that provide communication between the central nervous system and organs throughout the body . ‫یتكون‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫التي‬ ‫تربط‬ ‫بین‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫واألعضاء‬ ‫المختلفة‬ ‫في‬ ‫جمیع‬ ‫أنحاء‬ ‫الجسم‬ . •The peripheral nervous system can be subdivided into two divisions: •Afferent •Efferent ‫یمكن‬ ‫تقسیم‬ PNS ‫إلى‬ ‫قسمین‬ : ‫أفاران‬. ‫وابران‬
  • 2. •Nerve cells of the afferent division transmit information from the organs to the central nervous system. ‫تحمل‬ ‫الخالیا‬ ‫العصبیة‬ ‫األفارانیة‬ ‫المعلومات‬ ‫من‬ ‫األعضاء‬ ‫إلى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ . •Information transmitted to the central nervous system includes sensory information pertaining to the external environment (such as touch, temperature, vision, and sound) and visceral information pertaining to the internal environment (such as fullness of the stomach, blood pressure, and blood pH) ‫تتضمن‬ ‫المعلومات‬ ‫المرسلة‬ ‫إلى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫المعلومات‬ ‫الحسیة‬ ‫الواردة‬ ‫من‬ ‫البیئة‬ ‫الخارجیة‬ ( ‫مثل‬ ‫اللمس‬ ‫ودرجة‬ ‫الحرارة‬ ‫والبصر‬ ‫والصوت‬ ) ‫باإلضافة‬ ‫إلى‬ ‫المعلومات‬ ‫العمیقة‬ ‫الواردة‬ ‫من‬ ‫البیئة‬ . ‫داخل‬ ‫الجسم‬ ( ‫مثل‬ ‫امتالء‬ ‫المعدة‬ ‫وضغط‬ ‫الدم‬ ‫ودرجة‬ ‫حموضة‬ ‫الدم‬ ) . •Nerve cells of the efferent division transmit information from the central nervous system to organs in the periphery, called effector organs that perform functions in response to commands from neurons. ‫تنقل‬ ‫الخالیا‬ ‫العصبیة‬ ‫الصادرة‬ ‫المعلومات‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫إ‬ ‫لى‬ ‫األعضاء‬ . ‫تسمى‬ ‫هذه‬ ‫األعضاء‬ ‫باألعضاء‬ ‫الوظیفیة‬ ، ‫وهي‬ ‫في‬ ‫الواقع‬ ‫أوامر‬ ‫إنهم‬ ‫یفعلون‬ . •Effector organs are usually muscles and glands. ‫عادة‬ ‫ما‬ ‫تكون‬ ‫األعضاء‬ ‫النشطة‬ ‫عبارة‬ ‫عن‬ ‫عضالت‬ ‫وغدد‬ . •A neuron capable of transmitting messages to an effector organ is said to innervate that effector organ. ‫إن‬ ‫العصب‬ ‫الذي‬ ‫لدیه‬ ‫القدرة‬ ‫على‬ ‫نقل‬ ‫رسالة‬ ‫إلى‬ ‫عضو‬ ‫نشط‬ ‫هو‬ ‫في‬ ‫الواقع‬ ‫یعصب‬ ‫األعضاء‬ ‫النشطة‬ .
  • 3. •The efferent division can be further subdivided into two main branches: •Somatic nervous system (SNS) •Autonornic nervous system (ANS) ‫ینقسم‬ ‫الجزء‬ ‫الصادر‬ ‫إلى‬ ‫جزأین‬ ‫رئیسیین‬ : ‫الجهاز‬ ‫العصبي‬ ‫للجسم‬ (SNS) ، ‫والجهاز‬ ‫العصبي‬ ‫الالإرادي‬ (ANS) •The somatic nervous system consists of the nerve cells (called motor neurons) that regulate skeletal muscle contractions. ‫تحتوي‬ SNS ‫على‬ ‫خالیا‬ ‫عصبیة‬ ‫تتحكم‬ ‫في‬ ‫تقلصات‬ ‫العضالت‬ ‫الهیكلیة‬ ( ‫الخالیا‬ ‫العصبیة‬ ‫الحركیة‬ ) •The autonomic nervous system consists of nerve cells that regulate the function of internal organs and other structures (such as sweat glands and blood vessels) that are not under voluntary control. ‫یتكون‬ S ( ‫الجهاز‬ ‫العصبي‬ ‫الالإرادي‬ ) ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫التي‬ ‫تتحكم‬ ‫في‬ ‫األعضاء‬ ‫الداخلیة‬ ‫والبنى‬ ‫الداخلیة‬ ‫األخرى‬ ‫التي‬ ‫تفتقر‬ ‫هي‬ ‫الضوابط‬ ‫الطوعیة‬ ( ‫مثل‬ ‫الغدد‬ ‫العرقیة‬ ‫واألوعیة‬ ‫الدمویة‬ ) . •The autonomic nervous system can be divided into two branches: •Parasympathetic nervous systems •Sympathetic nervous systems
  • 4. ‫ینقسم‬ ‫الجهاز‬ ‫العصبي‬ ‫السمبثاوي‬ ‫نفسه‬ ‫إلى‬ ‫فرعین‬ ‫رئیسیین‬ : ‫الجهاز‬ ‫العصبي‬ ‫السمبثاوي‬ ‫والجهاز‬ ‫العصبي‬ ‫الودي‬ •These two branches tend to have opoosite effects on organs. ‫عادة‬ ‫ما‬ ‫یكون‬ ‫لهذین‬ ‫الجهازین‬ ‫العصبیین‬ ‫تأثیرات‬ ‫معاكس‬ ‫ة‬ . •The body also has an enteric nervous system (ENS), which consists of an intricate network of nerve cells in the gastrointestinal tract that can function independently of the rest of the nervous system but communicates with the autonomic nervous system. ‫یحتوي‬ ‫الجسم‬ ‫ًا‬‫ض‬‫أی‬ ‫على‬ ‫جهاز‬ ‫عصبي‬ ‫آخر‬ ‫یسمى‬ ‫الجهاز‬ ‫العصبي‬ ‫المعوي‬ (ENS) ، ‫وهو‬ ‫عبارة‬ ‫عن‬ ‫شبكة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجهاز‬ ‫الهضمي‬ . ‫یمكن‬ ‫أن‬ ‫یعمل‬ ‫بشكل‬ ‫مستقل‬ ‫عن‬ ‫أجزاء‬ ‫أخرى‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ، ‫ولكن‬ ‫لدیه‬ ‫ًا‬‫ض‬‫أی‬ ‫اتصاالت‬ ‫بالجهاز‬ ‫العصبي‬ ANS Cells of the Nervous System ‫خالیا‬ ‫الجهاز‬ ‫العصبي‬ •The nervous system contains two main classes of cells : •Neurons •Glial cells ‫یحتوي‬ ‫الجهاز‬ ‫العصبي‬ ‫على‬ ‫مجموعتین‬ ‫من‬ ‫الخالیا‬ : ‫الخالیا‬ ‫العصبیة‬ ‫والخالیا‬ ‫الدبقیة‬ •Neurons, or nerve cells, are" excitable cells "that communicate by transmitting electrical impulses . ‫الخالیا‬ ‫العصبیة‬ ، ‫أو‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫هي‬ ‫خالیا‬ ‫قابلة‬ ‫لإلثارة‬ ‫تتواصل‬ ‫مع‬ ‫بعضها‬ ‫البعض‬ ‫عن‬ ‫طریق‬ ‫النبضات‬ ‫الكهربائیة‬ •Excitable cells are defined as cells capable of producing large, rapid electrical signals called action potentials ‫ا‬ ‫لخالیا‬ ‫العصبیة‬ ‫هي‬ ‫الخالیا‬ ‫التي‬ ‫لدیها‬ ‫القدرة‬ ‫على‬ ‫إنتاج‬ ‫إشارات‬ ‫كهربائیة‬ ‫كبیرة‬ ‫وسریعة‬ ( ‫تسمى‬ ‫جهود‬ ‫الفعل‬ ) . •In the nervous system, the neuron is the functional unit ,the smallest unit of a tissue that can carry out the function of that tissue. ‫في‬ ‫الجهاز‬ ‫العصب‬ ‫ي‬ ، ‫الخالیا‬ ‫العصبیة‬ ‫هي‬ ‫وحدات‬ ‫التمثیل‬ ، ‫وهي‬ ‫في‬ ‫الواقع‬ ‫أصغر‬ ‫اللبنات‬ ‫األساسیة‬ ‫لألنسجة‬ ‫العصبیة‬ .
  • 5. •Glial cells ,which constitute 90% of the cells in the nervous system, provide various types of support to the neurons, including structural and metabolic support ‫تحتوي‬ ‫الخالیا‬ ‫الدبقیة‬ ، ‫التي‬ ‫تشكل‬ 09 ٪ ‫من‬ ‫خالیا‬ ‫الجهاز‬ ‫العصبي‬ ، ‫على‬ ‫مجموعة‬ ‫متنوعة‬ ‫من‬ ‫الوظائف‬ ‫الداعمة‬ ‫للخالیا‬ ‫العصبیة‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ ‫الدعم‬ ‫الهیكلي‬ ‫والتمثیل‬ ‫الغذائي‬ Neurons ‫الخالیا‬ ‫العصبیة‬ •Most neurons contain three main components: ‫تتكون‬ ‫معظم‬ ‫الخالیا‬ ‫العص‬ ‫بیة‬ ‫من‬ ‫ثالثة‬ ‫أجزاء‬ ‫رئیسیة‬ : •A cell body ‫جسم‬ ‫أو‬ ‫جسم‬ ‫الخلیة‬ •Two types of neural processes that extend from the cell body : the dendrite(s) and an axon. ‫نوعان‬ ‫من‬ ‫تكاثر‬ ‫الخالیا‬ ‫التي‬ ‫تركت‬ ‫جسم‬ ‫الخلیة‬ : ‫التشعبات‬ ‫والمحور‬ ‫العصبي‬ •The cell body (or soma) contains the cell nucleus and most of the cell's organelles; ‫یحتوي‬ ‫جسم‬ ‫الخلیة‬ ، ‫أو‬ ‫سوما‬ ، ‫على‬ ‫نواة‬ ‫ومعظم‬ ‫أعضاء‬ ‫الخلیة‬ . •It carries out most of the functions that other cells perform, such as protein synthesis and cellular metabolism . ‫یقوم‬ ‫جسم‬ ‫الخلیة‬ ‫بمعظم‬ ‫األشیا‬ ‫ء‬ ‫التي‬ ‫تقوم‬ ‫بها‬ ‫الخالیا‬ ‫األخرى‬ ، ‫مثل‬ ‫تخلیق‬ ‫البروتین‬ ‫والتمثیل‬ ‫الغذائي‬ ‫الخلوي‬ . •Although they have a nucleus, mature neurons lose the ability to undergo cell division. ‫على‬ ‫الرغم‬ ‫من‬ ‫أن‬ ‫هذه‬ ‫الخالیا‬ ‫لها‬ ‫نوى‬ ، ‫إال‬ ‫أن‬ ‫الخالیا‬ ‫العصبیة‬ ‫البالغة‬ ‫تفتقر‬ ‫إلى‬ ‫القدرة‬ ‫عل‬ ‫ى‬ ‫االنقسام‬ .
  • 6. •Thus in most areas of the nervous system, adults have all the neurons they will ever have. ‫وهكذا‬ ، ‫في‬ ‫معظم‬ ‫أجزاء‬ ‫الجهاز‬ ‫العصبي‬ ، ‫تبقى‬ ‫الخالیا‬ ‫العصبیة‬ ‫طوال‬ ‫الحیاة‬ . •However, we now know that in a few areas of the adult human brain new neurons can develop from undifferentiated cells (Neurogenesis) ‫ومع‬ ‫ذلك‬ ، ‫فقد‬ ‫أظهرت‬ ‫الدراسات‬ ‫الحدیثة‬ ‫أنه‬ ‫في‬ ‫بعض‬ ‫مناطق‬ ‫الدماغ‬ ‫البشري‬ ‫البالغ‬ ، ‫تتكون‬ ‫الخالیا‬ ‫العصبیة‬ ‫من‬ ‫خالیا‬ ‫غیر‬ ‫متمایزة‬ ‫تكوین‬ ‫الخالیا‬ ‫العصبیة‬ . •Dendrites branch from the cell body and receive input from other neurons at specialized junctions called synapses (Cell bodies themselves can also receive synaptic input). ‫تتفرع‬ ‫التشعبات‬ ‫خارج‬ ‫جسم‬ ‫الخلیة‬ ‫وتتلقى‬ ‫المعلومات‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫األخرى‬ ‫عند‬ ‫وصالت‬ ‫محددة‬ ‫تسمى‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ ( ‫الجسم‬ ‫نفسه‬ ) . ‫تصنع‬ ‫ال‬ ‫خلیة‬ ‫ًا‬‫ض‬‫أی‬ ‫مستقبالت‬ ‫متشابكة‬ •At a synapse, a presynaptic cell releases a chemical messenger called a neurotransmitter that usually communicates with the dendrite or cell body of a postsynaptic cell ‫نام‬ ‫به‬ ‫ویژهای‬ ‫شیمیایی‬ ‫مواد‬ ‫پیشسیناپسی‬ ‫سلول‬ ،‫سیناپس‬ ‫یک‬ ‫در‬ ‫سلولی‬ ‫جسم‬ ‫یا‬ ‫دندریتها‬ ‫با‬ ‫که‬ ‫میکند‬ ‫رها‬ ‫خود‬ ‫از‬ ‫را‬ ‫نوروترانسمیر‬ ‫پس‬ ‫نورون‬- ‫میکند‬ ‫برقرار‬ ‫ارتباط‬ ‫سیناپسی‬ . •Neurons have another branch that comes off the cell body called an axon ,or nerve fiber. ‫للخالیا‬ ‫العصبیة‬ ‫فرع‬ ‫آخر‬ ( ‫یتفرع‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ ) ‫یسمى‬ ‫محور‬ ‫عصبي‬ ‫أو‬ ‫ل‬ ‫یف‬ ‫عصبي‬ . •Unlike a dendrite, whose function is to receive information, an axon's job is to send information. ‫على‬ ‫عكس‬ ‫التشعبات‬ ، ‫تلعب‬ ‫المحاور‬ ‫دور‬ ‫إرسال‬ ‫المعلومات‬ . •Generally, a neuron has only one axon, but axons can branch and thus send signals to more than one destination.
  • 7. ‫عادة‬ ، ‫تحتوي‬ ‫الخلیة‬ ‫العصبیة‬ ‫على‬ ‫محور‬ ‫عصبي‬ ‫واحد‬ ‫فقط‬ ، ‫ولكن‬ ‫یمكن‬ ‫أن‬ ‫یتفرع‬ ‫المحور‬ ‫العصبي‬ ‫ویرسل‬ ‫إشارات‬ ‫إلى‬ ‫أكثر‬ ‫من‬ ‫وجهة‬ ‫واحدة‬ . •The branches of an axon are called collaterals, and like dendrites, the extent of branching varies among neurons and is indicative of the amount of communication with other cells. ‫تسمى‬ ‫الفروع‬ ‫المحوریة‬ ‫الضمانات‬ ، ‫ومثل‬ ‫التشعبات‬ ، ‫یختلف‬ ‫طولها‬ ‫ویشیر‬ ‫إلى‬ ‫مقدار‬ ‫االتصال‬ ‫بالخالیا‬ ‫األخرى‬ . •The axon functions is the transmission of information over relatively long distances in the form of electrical signals called action potentials ‫تتمثل‬ ‫وظیفة‬ ‫المحور‬ ‫العصبي‬ ‫في‬ ‫نقل‬ ‫المعلومات‬ ‫في‬ ‫شكل‬ ‫إشارات‬ ‫كهربائیة‬ ( ‫تسمى‬ ‫إمكانات‬ ‫الفعل‬ ) ‫عبر‬ ‫مسار‬ ‫طویل‬ ‫ًا‬‫ی‬‫نسب‬ . •The beginning and end of an axon are specialized structures called the axon hillock and the axon terminal, respectively. ‫تحتوي‬ ‫بدایة‬ ‫ونهایة‬ ‫المحور‬ ‫العصبي‬ ‫على‬ ‫هیاكل‬ ‫خاصة‬ ‫تسمى‬ ‫نتوءات‬ ‫محور‬ ‫عصبي‬ ‫ومحطات‬ ‫محوریة‬ ، ‫على‬ ‫التوالي‬ . • The axon hillock, the site where the axon originates from the cell body, is specialized in most neurons for the initiation of action potentials . ‫االنتفاخ‬ ‫المحوري‬ ( ‫حیث‬ ‫ینشأ‬ ‫المحور‬ ‫العصبي‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ ) ‫هو‬ ‫المكان‬ ‫الذي‬ ‫یبدأ‬ ‫فیه‬ ‫جهد‬ ‫الفعل‬ . •Once initiated, action potentials are transmitted to the axon terminal. ‫عندما‬ ‫یتم‬ ‫إنشاء‬ ‫جهد‬ ‫الفعل‬ ، ‫یتم‬ ‫توجیه‬ ‫هذه‬ ‫اإلمكانات‬ ‫إلى‬ ‫الم‬ ‫حطة‬ ‫المحوریة‬ . •The axon terminal is specialized to release a neurotransmitter upon arrival of an action potential . ‫خصائص‬ ‫المحطة‬ ‫المحوریة‬ ‫هي‬ ‫أنه‬ ‫عندما‬ ‫یتم‬ ‫الوصول‬ ‫إلى‬ ‫جهد‬ ‫الفعل‬ ، ‫فإنه‬ ‫یطلق‬ ‫الناقل‬ ‫العصبي‬ . •The released neurotransmitter molecules carry a signal to a postsynaptic cell, usually to a dendrite or the cell body of another neuron or to the cells of an effector organ. ‫ترسل‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫التي‬ ‫تم‬ ‫إطالقها‬ ‫إشارة‬ ‫عصبیة‬ ‫إلى‬ ‫خلیة‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫والتي‬ ‫عادة‬ ‫ما‬ ‫تكون‬ ‫التشعبات‬ ‫أو‬ ‫جسم‬ ‫الخلیة‬ ‫للخالیا‬ ‫ال‬ ‫عصبیة‬ ‫أو‬ ‫خالیا‬ ‫العضو‬ ‫التالیة‬ . ‫إنه‬ ‫عملي‬ ، ‫یحترقون‬ .
  • 8.
  • 9.
  • 10. The opening or closing of ion channels changes the permeability of the plasma membrane for a specific ion, resulting in ion movement across the membrane that causes a change in the electrical properties of the cell or triggers the release of a neurotransmitter .
  • 11. ‫یؤدي‬ ‫إغالق‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ‫إلى‬ ‫تغییر‬ ‫نفاذیة‬ ‫غشاء‬ ‫البالزما‬ ‫لبعض‬ ‫األیونات‬ ‫ونتیجة‬ ‫لذلك‬ ‫تمر‬ ‫األیونات‬ ‫عبر‬ ‫عرض‬ ‫الغشاء‬ ‫وبالتالي‬ ‫یتم‬ ‫تغییر‬ ‫الخصائص‬ ‫الكهربائیة‬ ‫للخلیة‬ ‫أو‬ ‫تحفیز‬ ‫إطالق‬ ‫الن‬ ‫اقالت‬ ‫العصبیة‬ . •Leak channels ,which are found in the plasma membrane throughout a neuron, are always open and are responsible for the resting membrane potential. ‫تكون‬ ‫قنوات‬ ‫التسرب‬ ‫الموجودة‬ ‫في‬ ‫جمیع‬ ‫أجزاء‬ ‫غشاء‬ ‫البالزما‬ ‫العصبیة‬ ‫مفتوحة‬ ‫ا‬ً‫م‬‫دائ‬ ‫وهي‬ ‫مسؤولة‬ ‫عن‬ ‫إ‬ ‫مكانات‬ ‫الراحة‬ ‫للغشاء‬ . •Ligand-gated channels open or close in response to the binding of a chemical messenger to a specific receptor in the plasma membrane. In neurons, ligand-gated channels are located in the dendrites and cell body (areas that receive communication from presynaptic neurons in the form of neurotransmitters). ‫تفتح‬ ‫قنوات‬ Ligand ‫أو‬ ‫تغلق‬ ً‫ة‬‫استجاب‬ ‫الرتباط‬ ‫المواد‬ ‫الكیمیائیة‬ ‫بمستقبالت‬ ‫محددة‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ . ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫قنوات‬ ‫یجند‬ ‫یوجد‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫التشعبات‬ ‫وجسم‬ ‫الخلیة‬ ( ‫المناطق‬ ‫ال‬ ‫تي‬ ‫یتم‬ ‫فیها‬ ‫إجراء‬ ‫الوصالت‬ ‫العصبیة‬ ‫بواسطة‬ ‫الناقالت‬ ‫العصبیة‬ ‫للخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ . ‫منجز‬ •Voltage-gated channels open or close in response to changes in membrane potential. ‫یتم‬ ‫سماع‬ ‫قنوات‬ ‫الجهد‬ ‫استجابة‬ ‫إلمكانیة‬ ‫عمل‬ ‫األغشیة‬ ‫المفتوحة‬ ‫أو‬ ‫المغلقة‬ . •Voltage-gated sodium channels and voltage-gated potassium channels are located throughout the neuron, but most densely in the axon and in greatest density in the axon hillock, and are necessary for the initiation and propagation of action potentials. ‫تنتشر‬ ‫قنو‬ ‫ات‬ ‫جهد‬ ‫الصودیوم‬ ‫والبوتاسیوم‬ ‫في‬ ‫جمیع‬ ‫أنحاء‬ ‫غشاء‬ ‫البالزما‬ ‫العصبیة‬ ، ‫ولكن‬ ‫أعلى‬ ‫كثافة‬ ‫لها‬ ‫تكون‬ ‫في‬ ‫المحاور‬ ، ‫وخاصة‬ ‫االنتفاخ‬ . ‫إنه‬ ‫محور‬ ‫عصبي‬ . ‫هذه‬ ‫القنوات‬ ‫ضروریة‬ ‫لبدء‬ ‫وتوسیع‬ ‫إمكانات‬ ‫العمل‬ . •Voltage-gated calcium channels are located in the axon terminal, these channels open in response to the arrival of an action potential at the axon terminal. When these channels are open, calcium enters the cytosol or the axon terminal and triggers the release of neurotransmitter.
  • 12. ‫توجد‬ ‫قنوات‬ ‫جهد‬ ‫الكالسیوم‬ ‫في‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ‫وتفتح‬ ً‫ة‬‫استجاب‬ ‫إلمكانیة‬ ‫الفعل‬ . ‫عندما‬ ‫تفتح‬ ‫هذه‬ ‫القنوات‬ ، ‫یدخل‬ ‫الكالسیوم‬ ‫إلى‬ ‫الخلیة‬ ‫الخلویة‬ ‫أو‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ‫ویحفز‬ ‫إطالق‬ ‫الناقالت‬ ‫العصبیة‬ . Structural and functional Classification of Neurons ‫التصنیف‬ ‫الهیكلي‬ ‫والوظیفي‬ ‫للخالیا‬ ‫العصبیة‬ Structural Classification of Neurons ‫التصنیف‬ ‫الهیكلي‬ ‫للخالیا‬ ‫العصبیة‬ •Neurons can be classified structurally according to the number of processes (axons and dendrites) that project from the cell body ‫یمكن‬ ‫تصنیف‬ ‫الخالیا‬ ‫العصبیة‬ ‫ًا‬‫ی‬‫هیكل‬ ً‫ء‬‫بنا‬ ‫على‬ ‫عدد‬ ‫المحاور‬ ( ‫المحاور‬ ‫والتشعبا‬ ‫ت‬ ) ‫التي‬ ‫تتفرع‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ . •Unipolar neurons have a single projection from the cell body. ‫الخالیا‬ ‫العصبیة‬ ‫أحادیة‬ ‫القطب‬ ‫لها‬ ‫ملحق‬ ‫بجسم‬ ‫الخلیة‬ . •Bipolar neurons have two projections, an axon and a dendrite, projecting from the cell body. Typical bipolar cells include sensory nenrons for olfaction (smell) and vision. ‫تحتوي‬ ‫الخالیا‬ ‫العصبیة‬ ‫ثنائیة‬ ‫القطب‬ ‫على‬ ‫ملحقین‬ ‫یتفرعان‬ ‫من‬ ‫جسم‬ ‫الخلیة‬ ( ‫محور‬ ‫عصبي‬ ‫وتغصنات‬ ) . ‫هم‬ ‫البصر‬ ‫والرائحة‬ . •Other sensory neurons, including those for touch and pain, are pseudo-unipolar neurons, a subclass of bipolar neurons. Although only one process seems to extend in two directions from the cell body, there are actually two processes, an axon and a modified dendrite, that project from the cell body in opposite directions. The modified dendritic process is called the peripheral axon because it originates in the periphery with sensory receptors and functions as an axon in that it transmits action potentials. The axon process is called the central axon because it ends in the central nervous system, where it forms synapses with other neurons. ‫الخالیا‬ ‫العصبیة‬ ‫الحسیة‬ ‫األخرى‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ ‫العمود‬ ‫الفقري‬ ‫واأللم‬ ، ‫هي‬ ‫الخالیا‬ ‫العصبیة‬ ‫القطبیة‬ ‫الزائفة‬ ( ‫مجموعة‬ ‫فرعیة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫ثنائیة‬ ‫القطب‬ ) ، ‫على‬ ‫الرغم‬ ‫من‬ ‫أنها‬ ‫تبدو‬ ‫فقط‬
  • 13. ‫تغادر‬ ‫إحدى‬ ‫الزوائد‬ ‫جسم‬ ‫ال‬ ‫خلیة‬ ‫وتستمر‬ ‫في‬ ‫اتجاهین‬ ، ‫ولكن‬ ‫هناك‬ ‫بالفعل‬ ‫ملحقان‬ ، ‫أحدهما‬ ‫محوار‬ ‫واآلخر‬ ‫شجیري‬ ، ‫في‬ ‫كال‬ ‫االتجاهین‬ . ‫تستمر‬ ‫األضداد‬ . ‫تسمى‬ ‫هذه‬ ‫التشعبات‬ ‫الخاصة‬ ‫بالمحاور‬ ‫الطرفیة‬ ‫ألنها‬ ‫تنشأ‬ ‫من‬ ‫المستقبالت‬ ‫الحسیة‬ ، ‫ومثل‬ ‫المحاور‬ ، ‫تنقل‬ ‫جهد‬ ‫الفعل‬ . ‫زایده‬ ‫ُطلق‬‫ی‬ ‫على‬ ‫المحوار‬ ‫ًا‬‫ض‬‫أی‬ ‫اسم‬ ‫محو‬ ‫ر‬ ‫عصبي‬ ‫مركزي‬ ‫ألنه‬ ‫ینتهي‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫ویتشابك‬ ‫مع‬ ‫الخالیا‬ ‫العصبیة‬ ‫األخرى‬ ‫في‬ ‫هذه‬ ‫المنطقة‬ . •Multipolar neurons, the most common neurons, have multiple projections from the cell body; one projection is an axon, all the others are dendrites ‫تحتوي‬ ‫الفیرونات‬ ‫متعددة‬ ‫األقطاب‬ ، ‫والتي‬ ‫تعد‬ ‫ًا‬‫ض‬‫أی‬ ‫أكثر‬ ‫أنواع‬ ‫الخالیا‬ ‫العصبیة‬ ‫ًا‬‫ع‬‫شیو‬ ، ‫على‬ ‫العدید‬ ‫من‬ ‫الزوائد‬ ‫في‬ ‫جسم‬ ‫الخلیة‬ . ‫أحد‬ ‫هذه‬ ‫االمتدادات‬ ‫هو‬ ‫محور‬ ‫عصبي‬ ‫والباقي‬ ‫هو‬ ‫التشعبات‬ ‫نكون‬ .
  • 14.
  • 15.
  • 16. Functional Classification of Neurons ‫التصنیف‬ ‫الوظیفي‬ ‫للخالیا‬ ‫العصبیة‬ •There are three functional classes of neurons : •Efferent neurons ‫الخالیا‬ ‫العصبیة‬ ‫المرنة‬ •Afferent neurons ‫الخالیا‬ ‫العصبیة‬ ‫األفارانیة‬ • Interneurons. ‫الخالیا‬ ‫العصبیة‬ ‫الوسیطة‬ Efferent neurons transmit information from the central nervous system to effector organs. ‫تنقل‬ ‫الخالیا‬ ‫العصبیة‬ ‫الصادرة‬ ‫المعلومات‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫إلى‬ ‫األعضاء‬ ‫النشطة‬ . • Recall that efferent neurons include the motor neurons extending to skeletal muscle and neurons of the autonomic nervous system
  • 17. ‫وتجدر‬ ‫اإلشارة‬ ‫إلى‬ ‫أن‬ ‫الخالیا‬ ‫ال‬ ‫عصبیة‬ ‫الصادرة‬ ‫تشمل‬ ‫الخالیا‬ ‫العصبیة‬ ‫الحركیة‬ ( ‫العضالت‬ ‫الهیكلیة‬ ) ‫والخالیا‬ ‫العصبیة‬ ANS • The cell body and dendrites of efferent neurons are located in the central nervous system (autonomic postganglionic neurons, are an exception). ‫یقع‬ ‫جسم‬ ‫الخلیة‬ ‫والتشعبات‬ ‫ل‬ ‫لخالیا‬ ‫العصبیة‬ ‫الصادرة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ( ‫الخالیا‬ ‫العصبیة‬ ‫االرتجاعیة‬ ‫الالإرادیة‬ ‫هي‬ ‫استثناء‬ ) . • The axon leaves the central nervous system and becomes part of the peripheral nervous system as it travels to the effector organ it innervates ‫تغادر‬ ‫محاو‬ ‫ر‬ ‫هذه‬ ‫الخالیا‬ ‫العصبیة‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫وكجزء‬ ‫من‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ (PNS) ‫تذهب‬ ‫إلى‬ ‫األعضاء‬ ‫النشطة‬ ‫وتعصبها‬ . •The function of afferent neurons is to transmit either sensory information from sensory receptors (which detect information pertaining to the outside environment) or visceral information from visceral receptors (which detect information pertaining to conditions in the interior of the body) to the central nervous system for further processing . ‫تتمثل‬ ‫وظیفة‬ ‫الخالیا‬ ‫العصبیة‬ ‫الواردة‬ ‫في‬ ‫نقل‬ ‫المعلوم‬ ‫ات‬ ‫الحسیة‬ ‫من‬ ‫المستقبالت‬ ‫الحسیة‬ ( ‫التي‬ ‫تأخذ‬ ‫المعلومات‬ ‫من‬ ‫البیئة‬ ) ‫أو‬ ‫المعلومات‬ ‫الحشویة‬ ‫من‬ ‫المستقبالت‬ ‫یتم‬ ‫إرسال‬ ‫األحشاء‬ ( ‫التي‬ ‫تتلقى‬ ‫معلومات‬ ‫حول‬ ‫الظروف‬ ‫الداخلیة‬ ‫للجسم‬ ) ‫إلى‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫لمزید‬ ‫من‬ ‫المعالجة‬ . •Most afferent neurons are pseudo-unipolar neurons ,with the cell body located outside the central nervous system in a ganglion (the general term for a cluster of neural cell bodies located outside the CNS) ‫معظم‬ ‫الخالیا‬ ‫العصبیة‬ ‫الواردة‬ ‫هي‬ ‫عصبونات‬ ‫زائفة‬ ‫أحادیة‬ ‫القطب‬ ‫تكون‬ ‫أجسامها‬ ‫الخلویة‬ ‫خارج‬ ‫الجهاز‬ ‫الع‬ ‫صبي‬ ‫المركزي‬ ‫وفي‬ ‫العقد‬ ‫العصبیة‬. ‫من‬ ‫الشائع‬ ‫أن‬ ‫تتراكم‬ ‫أجسام‬ ‫الخالیا‬ ‫خارج‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ . •The endings of the peripheral axon are located in the peripheral organ (sensory organ or visceral organ), where they are either modified into sensory receptors or receive communication from separate sensory receptor cells . ‫تقع‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ‫المحیطي‬ ‫في‬ ‫األعضاء‬ ‫المحیطیة‬ ( ‫األعضاء‬ ‫الحسیة‬ ‫أو‬ ‫الحشویة‬ ) ، ‫أي‬ ‫حیث‬ ‫تذهب‬ ‫إلى‬ ‫المستقبالت‬ ‫الحسیة‬ ‫أو‬ ‫تجري‬ ‫اتصاالت‬ . ‫یتلقون‬ ‫مستقبالت‬ ‫حسیة‬ ‫منفصلة‬ ‫من‬ ‫الخالیا‬ .
  • 18. •The central axon terminates in the central nervous system, where it releases a neurotransmitter to communicate with other neurons. ‫ینتهي‬ ‫المحور‬ ‫المركزي‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ، ‫حیث‬ ‫یطلق‬ ‫نواقله‬ ‫العصبیة‬ ‫للتواصل‬ ‫مع‬ ‫الخالیا‬ ‫العصبیة‬ ‫األخرى‬ . •The third functional class of neurons is interneurons ,which account for 99% of all neurons in the body . ‫المجموعة‬ ‫الثالثة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ( ‫وظیفیا‬ ) ‫هي‬ ‫الخالیا‬ ‫العصبیة‬ ‫الوسیطة‬ ‫التي‬ ‫تشكل‬ 00 ٪ ‫من‬ ‫مجموع‬ ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجسم‬ . •They are located entirely in the central nervous system . ‫تقع‬ ‫بالكامل‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ . •Interneurons perform all the functions of the central nervous system ,including processing sensory information from afferent neurons, sending out commands to effector organs through efferent neurons, and carrying out complex functions of the brain such as thought, memory, and emotions. ‫الخالیا‬ ‫العصبیة‬ ‫الوسیطة‬ ‫جمیع‬ ‫وظائف‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ ‫معالجة‬ ‫المعلومات‬ ‫الحسیة‬ ‫الواردة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫الواردة‬ ، ‫وإرسال‬ ‫األوامر‬ ‫إلى‬ ‫األعضاء‬ ‫النشطة‬ . ‫من‬ ‫خالل‬ ‫الخالیا‬ ‫ا‬ ‫لعصبیة‬ ‫الصادرة‬ ، ‫وتؤدي‬ ‫العدید‬ ‫من‬ ‫وظائف‬ ‫الدماغ‬ ‫المعقدة‬ ‫مثل‬ ‫التفكیر‬ ‫والذاكرة‬ ‫والعواطف‬ .
  • 19.
  • 20. Structural Organization of Neurons in the Nervous System ‫التنظیم‬ ‫الهیكلي‬ ‫للخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ •Structural Organization of Neurons in the Nervous System Neurons are arranged within the nervous system in an orderly fashion, with those having similar functions tending to be grouped together. ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫لها‬ ‫ترتیب‬ ‫هرمي‬ ، ‫وتلك‬ ‫التي‬ ‫تعمل‬ ‫بشكل‬ ‫مشابه‬ ‫تشكل‬ ‫مجموعات‬ . •Neurons are aligned in such a way that cell bodies and dendrites of adjacent cells tend to be grouped together, and axons of adjacent cells tend to be grouped together.
  • 21. ‫یتم‬ ‫ترتیب‬ ‫الخالیا‬ ‫العصبیة‬ ‫بحیث‬ ‫تشكل‬ ‫أجسام‬ ‫الخالیا‬ ‫والتشعبات‬ ‫للخالیا‬ ‫المجاورة‬ ‫مجموعة‬ ‫مع‬ ‫بعضها‬ ‫البعض‬ ، ‫ومحاور‬ ‫للخالیا‬ ‫المجاورة‬ ‫هم‬ ‫أیضا‬ ‫یشكلون‬ ‫مجموعات‬ ‫مع‬ ‫بعضهم‬ ‫البعض‬ •In the central nervous system ,cell bodies of neurons are often grouped into nuclei (singular = nucleus), and the axons travel together in bundles called pathways, tracts, or commissures. ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المركزي‬ ، ‫ًا‬‫ب‬‫غال‬ ‫ما‬ ‫تتجمع‬ ‫أجسام‬ ‫الخالیا‬ ‫العصبیة‬ ‫داخل‬ ‫النوى‬ ، ‫وتتجمع‬ ‫المحاور‬ ‫في‬ ‫مجموعات‬ ‫تسمى‬ ‫المسارات‬ ‫أو‬ ‫الوصالت‬ ‫أو‬ ‫التقاطعات‬ . ‫وجدت‬ . •In the peripheral nervous system ,cell bodies of neurons are clustered together in ganglia (singular = ganglion), and the axons travel together in bundles called nerves ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ ، ‫تتجمع‬ ‫أجسام‬ ‫الخالیا‬ ‫العصبیة‬ ‫في‬ ‫عقد‬ ، ‫وتتجمع‬ ‫المحاور‬ ‫في‬ ‫مجموعات‬ ‫تسمى‬ ‫األعصاب‬ . Glial Cells ‫الخالیا‬ ‫الدبقیة‬ •Glial cells ,the second class of non-neural cells found in the nervous system, account for 90% of all cells in the nervous system. ‫الخالیا‬ ‫الدبقیة‬ - ‫ثاني‬ ‫أكبر‬ ‫مجموعة‬ ‫من‬ ‫الخالیا‬ ‫غیر‬ ‫العصبیة‬ ‫الموجودة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ - 09 ٪ ‫من‬ ‫جمیع‬ ‫الخالیا‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫یعطون‬ . •They do not function directly in signal transmission; instead, they provide structural integrity to the nervous system (glia is Latin for "glue”) and they are necessary for neurons to carry out their functions. ‫ال‬ ‫تلعب‬ ‫هذه‬ ‫الخالیا‬ ‫ا‬ ً‫دور‬ ‫ا‬ً‫مباشر‬ ‫في‬ ‫نقل‬ ‫اإلشارات‬ ‫العصبیة‬ ، ‫ولكنها‬ ً‫ال‬‫بد‬ ‫من‬ ‫ذلك‬ ‫توفر‬ ‫قوة‬ ‫هیكلیة‬ ‫للجهاز‬ ‫ا‬ ‫لعصبي‬ ‫إنه‬ ‫یعني‬ ‫الغراء‬ ( ‫وبالتالي‬ ‫فهو‬ ‫ضروري‬ ‫للتشغیل‬ ‫السلیم‬ ‫للخالیا‬ ‫العصبیة‬ .
  • 22. •There are five types of glial cells: •Astrocytes •Eependymal cells •Microglia •Oligodendrocytes •Schwann cells ‫هناك‬ ‫خمسة‬ ‫أنواع‬ ‫من‬ ‫الخالیا‬ ‫الدبقیة‬ : * ‫الخالیا‬ ‫القشریة‬ ‫أو‬ ‫الخال‬ ‫یا‬ ‫النجمیة‬ * ‫خالیا‬ ‫البطانة‬ ‫العصبیة‬ * ‫الخالیا‬ ‫الدبقیة‬ ‫الصغیرة‬ * ‫خالیا‬ Oligodendron * ‫خالیا‬ ‫شوان‬
  • 23. Astrocytes are critical role in formation of the blood-brain barrier (they stimulate endothelial cells to develop tight junctions by unknown mechanisms). ‫تل‬ ‫عب‬ ‫الخالیا‬ ‫القشریة‬ ‫ا‬ً‫دور‬ ‫ا‬ً‫م‬‫مه‬ ‫في‬ ‫تكوین‬ ‫الحاجز‬ ‫الدموي‬ ‫الدماغي‬ ، ‫فهي‬ ‫تحفز‬ ‫الخالیا‬ ‫البطانیة‬ ‫على‬ ‫تكوین‬ ‫روابط‬ ‫بواسطة‬ ‫آلیة‬ ‫غیر‬ ‫معروفة‬ . ‫تصبح‬ ‫صعبة‬ •Ependymal cells that lining the ventricles and central canal of CNS, are a type of epithelial cell ‫الخالیا‬ ‫البطان‬ ‫یة‬ ‫العصبیة‬ ‫التي‬ ‫تبطن‬ ‫بطینات‬ ‫الدماغ‬ ‫والقناة‬ ‫المركزیة‬ ‫للجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫هي‬ ‫ظهاریة‬ . •Microglial cells are part of the supporting structure of CNS that are migratory and phagocytic (phagocyte the waste products of nerve tissue in CNS) ‫الخالیا‬ ‫الدبقیة‬ ‫الصغ‬ ‫یرة‬ ‫هي‬ ‫جزء‬ ‫من‬ ‫الهیكل‬ ‫الوقائي‬ ‫للجهاز‬ ‫العصبي‬ ‫المركزي‬ ‫ولها‬ ‫خاصیة‬ ‫الهجرة‬ ‫والبلعمة‬ ( ‫البلعمة‬ ) ‫من‬ ‫إفرازات‬ ‫األنسجة‬ ‫العصبیة‬ ‫في‬ CNS) ‫لها‬
  • 24. •Oligodendrocytes and Schwann cells are crucial role in electrical transmission of neurons ‫تلعب‬ ‫خالیا‬ Oligodendral ‫و‬ Schwann ‫دو‬ ‫ا‬ً‫ر‬ ‫ا‬ً‫م‬‫مه‬ ‫في‬ ‫النقل‬ ‫الكهربائي‬ ‫للخالیا‬ ‫العصبیة‬ •The primary function of oligodendrocytes and Schwann cells is to form an insulating wrap of myelin around the axons of neurons. ‫یتمثل‬ ‫الدور‬ ‫الرئیسي‬ ‫لخالیا‬ oligodendral ‫و‬ Schwann ‫في‬ ‫إنشاء‬ ‫غمد‬ ‫المایلین‬ ‫حول‬ ‫المح‬ ‫اور‬ ‫العصبیة‬ •Such insulation enables neurons to transmit action potentials more efficiently and rapidly. ‫تزید‬ ‫هذه‬ ‫العزلة‬ ‫من‬ ‫سرعة‬ ‫وكفاءة‬ ‫انتقال‬ ‫الفعل‬ ‫المحتمل‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ . •Myelin consists of concentric layers of the cell membranes of either oligodendrocytes or Schwann cells ‫یحتوي‬ ‫المیالین‬ ‫على‬ ‫طبقات‬ ‫متحدة‬ ‫المركز‬ ‫من‬ ‫أغشیة‬ ‫الخالیا‬ ‫لخالیا‬ ‫قلیلة‬ ‫التغصن‬ ‫وخالیا‬ ‫شوان‬ . •Oligodendrocytes form myelin around axons in the central nervous system ‫تشكل‬ ‫الخالیا‬ ‫قلیلة‬ ‫التغصن‬ ‫غشاء‬ ‫المایلین‬ ‫حول‬ ‫محاور‬ ‫عصبیة‬ ‫في‬ ‫الجهاز‬ ‫الع‬ ‫صبي‬ ‫المركزي‬ . •One oligodendrocyt sends out projections providing the myelin segments for many axons ‫تنضح‬ ‫خلیة‬ oligodendron ‫الزوائد‬ ‫التي‬ ‫تشكل‬ ‫غشاء‬ ‫المایلین‬ ‫لعدة‬ ‫محاور‬ •Schwann calls form myelin around axons in the peripheral nervous system ,but each Schwann cell provides myelin for only one axon ‫تشكل‬ ‫خالیا‬ ‫شوان‬ ‫غشاء‬ ‫المایلین‬ ‫على‬ ‫المحاور‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫المحیطي‬ ، ‫لكن‬ ‫كل‬ ‫خلیة‬ ‫شوان‬ ‫تنتج‬ ‫ا‬ً‫محوار‬ ‫ًا‬‫د‬‫واح‬ ‫فقط‬ ‫من‬ ‫غشاء‬ ‫المایلین‬ . ‫یفعل‬ . •Many oligodendrocytes or Schwann cells are needed to provide the myelin for a single axon. ‫هناك‬ ‫حاجة‬ ‫إلى‬ ‫عدة‬ ‫خالیا‬ oligodendron ‫أو‬ Schwann ‫إلنتاج‬ ‫المایلین‬ ‫من‬ ‫محور‬ ‫عصبي‬ •Because the lipid bilayer of a cell membrane has low permeability to ions, the several layers of membrane that make up a myelin sheath substantially reduce leakage of ions across the cell membrane ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫الغشاء‬ ‫الخلوي‬ ‫ثنائي‬ ‫الطبقة‬ ‫الدهنیة‬ ‫له‬ ‫نفاذیة‬ ‫منخفضة‬ ‫لألیونات‬ ، ‫یمكن‬ ‫أن‬ ‫تكون‬ ‫طبقات‬ ‫عدیدة‬ ‫من‬ ‫غشاء‬ ‫الخلیة‬ ‫التي‬ ‫یتكون‬ ‫منها‬ ‫غشاء‬ ‫المایلین‬ ‫بشكل‬ ‫ملحوظ‬ ‫یقلل‬ ‫بشكل‬ ‫كبیر‬ ‫من‬ ‫نفاذیة‬ ‫األیونات‬ ‫من‬ ‫غشاء‬ ‫الخلیة‬ ‫للخالیا‬ ‫العصبیة‬ .
  • 25. •However in gaps in the myelin, called nodes of Ranvier ,The axonal membrane contains voltage-gated sodium and potassium channels that function in the transmission of action potentials by allowing ion movement across the membrane. ‫ومع‬ ‫ذلك‬ ، ‫في‬ ‫مناطق‬ ‫من‬ ‫غشاء‬ ‫ا‬ ‫لمیالین‬ ‫تسمى‬ ‫العقد‬ ‫الكلویة‬ ، ‫یحتوي‬ ‫غشاء‬ ‫المحور‬ ‫العصبي‬ ‫على‬ ‫قنوات‬ ‫جهد‬ ‫الصودیوم‬ ‫والبوتاسیوم‬ ‫التي‬ ‫تمر‬ ‫عبرها‬ . ‫األیونات‬ ‫تنقل‬ ‫الجهد‬ ‫من‬ ‫الغشاء‬ .
  • 26.
  • 27.
  • 28.
  • 29.
  • 30.
  • 31.
  • 32.
  • 33. Types of nerve fiber ‫أنواع‬ ‫األلیاف‬ ‫العصبیة‬ •A fibers : ‫ألیاف‬ ‫من‬ ‫النوع‬ ‫أ‬ •Myelinated afferent or efferent fibers of somatic nervous system having a diameter of 2 to 20 micron and conduction velocity of 12 to 120 meter per second; they include alpha, beta, gamma and delta fibers
  • 34. ‫األفاران‬ ‫واأللیاف‬ ‫النخاعیة‬ ‫الصادرة‬ ، ‫الجهاز‬ ‫العصبي‬ ، SNS ( ‫ا‬ ‫لجسم‬ ( 2 ‫إلى‬ 29 ‫میكرون‬ ‫في‬ ‫القطر‬ ‫و‬ 22 ‫إلى‬ 229 ‫ا‬ً‫متر‬ ‫في‬ ‫الثانیة‬ ) ‫وهي‬ ‫تشمل‬ ‫ألفا‬ ‫وبیتا‬ ‫وجاما‬ ‫ودلتا‬ . •A alpha fibers : ‫ألیاف‬ ‫نوع‬ ‫ألفا‬ •Motor and proprioceptive fibers of the A type having conduction velocities of 70 to 120 meter per second and ranging from 12 to 20 micron in diameter ‫نوع‬ ‫ألفا‬ ‫أ‬ : ‫األلیاف‬ ‫الحسیة‬ ‫والحسیة‬ ‫العمیقة‬ ، ‫استقبال‬ ‫الرسائل‬ ‫الحسیة‬ ‫من‬ ‫أعماق‬ ‫الجسم‬ ( ‫النوع‬ ‫أ‬ ، ‫بمعدل‬ ‫نقل‬ ‫من‬ 09 ‫إلى‬ 229 ‫متر‬ ‫في‬ ‫الثانیة‬ ‫واألقطار‬ ‫من‬ 22 ‫إلى‬ 29 ‫میكرون‬ . •A beta fibers : •Motor and proprioceptive fibers of the A type having conduction velocities of 30 to 70 meter per second and ranging from 5 to 12 micron in diameter ‫ألیاف‬ ‫بیتا‬ ‫من‬ ‫النوع‬ A: ‫محرك‬ ‫عمیق‬ ‫وألیاف‬ ‫حسیة‬ ‫لها‬ ‫معدل‬ ‫نقل‬ ‫من‬ 09 ‫إلى‬ 09 ‫متر‬ ‫في‬ ‫الثانیة‬ ‫وقطر‬ ‫من‬ 5 ‫إلى‬ 22 ‫میكرون‬ •A gamma fibers : •Fibers of the A type having conduction velocities of 15 to 30 meter per second and ranging from 3 to 6 micron in diameter. These fiber are fusimotor fiber (modified muscle fibers which surrounded by fluid and enclosed in connective tissue envelope, compose the muscle spindle). ‫ألیا‬ ‫ف‬ ‫جاما‬ ‫من‬ ‫النوع‬ ‫أ‬ : ‫سرعة‬ ‫النقل‬ ‫من‬ 25 ‫إلى‬ 09 ‫متر‬ ‫في‬ ‫الثانیة‬ ‫وقطرها‬ ‫من‬ 0 ‫إلى‬ 6 ‫میكرون‬ . ‫هذه‬ ‫األلیاف‬ ‫هي‬ ‫ألیاف‬ fusimotor ‫عضالت‬ ‫مشوهة‬ ‫محاطة‬ ‫بسائل‬ ‫وتقع‬ ‫في‬ ‫غمد‬ ‫من‬ ‫النسیج‬ ‫الضام‬ . •A delta fibers : •A type of small myelinated afferent A fibers that respond to pressure, temperature, or chemical stimuli, conducting from the cutaneous tissues the initial stimulus perceived as the primary painful event. Their conducting velocity is low, about the same as that of B fibers ‫ألیاف‬ ‫دلتا‬ ‫من‬ ‫النوع‬ A: ‫نوع‬ ‫من‬ ‫األلیاف‬ A ‫تكون‬ ‫صادرة‬ ‫ومخلفة‬ ‫وتستجیب‬ ‫لمحفزات‬ ‫انضغاطیة‬ ‫أو‬ ‫حراریة‬ ‫أو‬ ‫كیمیائیة‬ ‫من‬ ‫أنسجة‬ ‫الجلد‬ ‫معدل‬ ‫نقل‬ ‫هذه‬ ‫األلیاف‬ ‫منخفض‬ ‫وحوالي‬ ‫األلیاف‬ ‫ب‬ . •B fibers : ‫ألیاف‬ ‫ب‬
  • 35. •Myelinated preganglionic autonomic axons having conduction velocities of 3 to 15 meter per second and ranging from 1 to 3 micron in diameter. ‫محاور‬ ‫أمامیة‬ ‫ذاتیة‬ ‫النخاع‬ ‫بسرعة‬ ‫نقل‬ ‫من‬ 0 ‫إلى‬ 25 ‫ا‬ ً‫متر‬ ‫في‬ ‫الثانیة‬ ‫وقطرها‬ ‫من‬ 2 ‫إلى‬ 0 ‫میكرون‬ . •These include only efferent fibers ‫هذه‬ ‫األلیاف‬ ‫هي‬ ‫فقط‬ ‫من‬ ‫النوع‬ ‫الصادر‬ . •C fibers : ‫ألیاف‬ ‫ج‬ •Unmyelinated nerve fibers, having slower conduction velocities (0.7 to 2.3 meter per second) and smaller diameter (0.3 to 1.3 micron) than alpha fibers ‫ألیاف‬ ‫غیر‬ ‫المیالنین‬ ‫ذات‬ ‫معدل‬ ‫نقل‬ ‫أقل‬ ( 0.9 ‫إلى‬ 0.2 ‫م‬ / ‫ث‬ ( ‫وقطرها‬ ‫أصغر‬ ‫من‬ ‫ألیاف‬ ‫ألفا‬ ( ) 0.9 ‫إلى‬ 0.2 ‫میكرومتر‬ ) • They are found as postganglionic (efferent) fibers of the autonomic nervous system, and as afferent fibers at as thermoreceptors, nociceptors, and interoceptors ‫عرف‬ُ‫ت‬ ‫هذه‬ ‫األلیاف‬ ‫باأللیاف‬ ‫التبخیریة‬ ‫المرتجعة‬ ‫لنظام‬ ANS ‫واأللیاف‬ ‫الواردة‬ ‫مثل‬ ‫المستقبالت‬ ‫الحراریة‬ ‫وأعصاب‬ ‫األلم‬ ‫واألعصاب‬ ‫الحشویة‬ .
  • 36. Neural Integration ‫االستمراریة‬ ‫العصبیة‬ •Communication between neuruns, however, is not a one-to-one relationship ‫االتصال‬ ‫بین‬ ‫الخالیا‬ ‫العصبیة‬ ‫لیس‬ ‫مجرد‬ ‫اتصال‬ ‫واحد‬ ‫لواحد‬ .
  • 37. •In some cases many neurons communicate with a given neuron, an arrangement called convergence ‫في‬ ‫بعض‬ ‫الحاالت‬ ، ‫ترتبط‬ ‫العدید‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫بخالیا‬ ‫عصبیة‬ ‫واحدة‬ ، ‫وهو‬ ‫ترتیب‬ ‫یسمى‬ ‫التقارب‬ . •In convergence, a neuron must function as an integrator ,taking in informalion from several different sources in the form of graded potentials ,summing it, and then on the basis of the results, either generating an action potential or not ‫عند‬ ‫التقارب‬ ، ‫تعمل‬ ‫الخلیة‬ ‫العصبیة‬ ‫كمولد‬ ‫للتحالف‬ ، ‫وتجمع‬ ‫المعلومات‬ ‫من‬ ‫عدة‬ ‫مصادر‬ ‫مختلفة‬ ‫ثم‬ ‫أ‬ ‫یخلق‬ ‫إمكانات‬ ‫فعلیة‬ ( ‫أو‬ ‫ال‬ ‫تخلق‬ ‫إمكانات‬ ‫فعلیة‬ ) . •In other cases the axon of one neuron branches into many terminals that communicate with many other cells, an arrangement called divergence ‫في‬ ‫حاالت‬ ‫أخرى‬ ، ‫یقسم‬ ‫المحور‬ ‫العصبي‬ ‫الخالیا‬ ‫العصبیة‬ ‫إلى‬ ‫عدة‬ ‫فروع‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫تكوین‬ ‫ترتیب‬ ‫یسمى‬ ‫متشعب‬ .
  • 39. •Neurons communicate at specialized structures called synapses. ‫تتواصل‬ ‫الخالیا‬ ‫العصبیة‬ ‫مع‬ ‫بعضها‬ ‫البعض‬ ‫في‬ ‫هیاكل‬ ‫خاصة‬ ‫تسمى‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ . •There are two types of synapses in the nervous system: ‫هناك‬ ‫نوعان‬ ‫من‬ ‫نقاط‬ ‫االشتباك‬ ‫ال‬ ‫عصبي‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ . •Electrical synapses •Chemical synapses • ‫المشابك‬ ‫الكهربائیة‬ • ‫المشابك‬ ‫الكیمیائیة‬ Electrical synapses Electrical synapses operate by allowing electrical signals to be transmitted directly from one neuron to another ;neurotransmitters are not involved . ‫تسمح‬ ‫المشابك‬ ‫الكهربائیة‬ ‫بنقل‬ ‫اإلشارات‬ ‫الكهربائیة‬ ‫مباشرة‬ ‫من‬ ‫خلیة‬ ‫عصبیة‬ ‫إلى‬ ‫أخرى‬ ‫دون‬ ‫استخدام‬ ‫الناقالت‬ ‫العصبیة‬ . •At these synapses the plasma membranes of adjacent cells are linked together by gap junctions such that when an electrical signal, such as an action potential, is generated in one cell, it is directly transferred to the adjacent cell by means of ions flowing through the gap junctions. ‫في‬ ‫هذه‬ ‫المشابك‬ ، ‫ترتبط‬ ‫أغشیة‬ ‫البالزما‬ ‫لخلیتین‬ ‫متجاورتین‬ ‫عن‬ ‫طریق‬ ‫وصالت‬ ‫وإشارة‬ ‫كهربائیة‬ ( ‫مثل‬ ‫یتم‬ ‫نقل‬ ‫جهد‬ ‫الفعل‬ ( ‫الذي‬ ‫تم‬ ‫إنشاؤه‬ ‫في‬ ‫خلیة‬ ‫مباشرة‬ ‫إلى‬ ‫الخلیة‬ ‫المجاورة‬ ) ‫عن‬ ‫طریق‬ ‫تدفق‬ ‫األیونات‬ ‫من‬ ‫فجوة‬ ‫الوصلة‬ . •Because the function of electrical synapses in the nervous system is not well understood, they will not be discussed any further here. ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫وظیفة‬ ‫المشابك‬ ‫الكهربائیة‬ ‫في‬ ‫الجهاز‬ ‫العصبي‬ ‫لم‬ ‫یتم‬ ‫توضیحها‬ ‫بشكل‬ ‫صحیح‬ ‫بعد‬ ، ‫فلن‬ ‫یتم‬ ‫شرحها‬ ‫بمزید‬ ‫من‬ ‫التفصیل‬ ‫هنا‬ . •However, gap junctions in smooth and cardiac muscle have an important role in enabling these muscles to contract as a unit .
  • 40. ‫فجوات‬ ‫التقاطع‬ ‫في‬ ‫ال‬ ‫عضالت‬ ‫الملساء‬ ‫وعضلة‬ ‫القلب‬ ‫لها‬ ‫دور‬ ‫مهم‬ ‫في‬ ‫تقلص‬ ‫هذه‬ ‫العضالت‬ ( ‫كوحدة‬ ) . CHEMICAL SYNAPSES ‫المشابك‬ ‫الكیمیائیة‬ •Almost all neurons transmit messages to other cells at chemical synapses. ‫تنقل‬ ‫جمیع‬ ‫الخالیا‬ ‫العصبیة‬ ‫ًا‬‫ب‬‫تقری‬ ‫رسائلها‬ ‫إلى‬ ‫الخالیا‬ ‫األخرى‬ ‫من‬ ‫خالل‬ ‫المشاب‬ ‫ك‬ ‫الكیمیائیة‬ . •In a chemical synapse, one neuron secretes a neurotransmitter into the extracellular fluid in response to an action potential arriving at its axon terminal . ‫في‬ ‫المشابك‬ ‫الكیمیائیة‬ ، ‫تفرز‬ ‫الخالیا‬ ‫العصبیة‬ ‫نقاط‬ ‫نهایة‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫السائل‬ ‫خا‬ ‫رج‬ ‫الخلیة‬ ً‫ة‬‫استجاب‬ ‫لقدرتها‬ ‫على‬ ‫الفعل‬ . ‫یفعل‬ . •The neurotransmitter then binds to receptors on the plasma membrane of a second cell, triggering in that cell an electrical signal that may or may not initiate an action potential, depending on a number of circumstances. ‫ثم‬ ‫یتصل‬ ‫الناقل‬ ‫العصبي‬ ‫بمستقبالت‬ ‫معینة‬ ‫على‬ ‫غشاء‬ ‫البالزما‬ ‫للخلیة‬ ‫الثانیة‬ ، ‫مما‬ ‫ینتج‬ ‫عنه‬ ‫إشارة‬ ‫كهربائیة‬ ‫قد‬ ‫قد‬ ‫یؤدي‬ ‫أو‬ ‫ال‬ ‫یؤدي‬ ‫إلى‬ ‫إجراء‬ ‫محتمل‬ ( ‫حسب‬ ‫ظروف‬ ‫معینة‬ ) . •A neuron can form synapses with other neurons or with effector cells such as muscle or gland cells. ‫یمكن‬ ‫أن‬ ‫تتكون‬ ‫الخالیا‬ ‫العصبیة‬ ‫مع‬ ‫خالیا‬ ‫عصبیة‬ ‫أخرى‬ ‫أو‬ ‫خالیا‬ ‫وظیفیة‬ ‫مثل‬ ‫خالیا‬ ‫العضالت‬ ‫أو‬ ‫الغدد‬ ‫المشبكیة‬ . •Muscles and glands are generally referred to as effector organs, and a synapse between a neuron and an effector cell is called a neuroeffector junction. ‫تسمى‬ ‫العضالت‬ ‫والغدد‬ ‫عادة‬ ‫باألعضاء‬ ‫العاملة‬ ، ‫ُطلق‬‫ی‬‫و‬ ‫على‬ ‫المشبك‬ ‫بین‬ ‫الخلیة‬ ‫العصبیة‬ ‫والخلیة‬ ‫العاملة‬ ‫تقاطع‬ ‫العامل‬ ‫العصبي‬ . •Neuroeffector junctions operate according to the same basic principles concerning neuron-to-neuron synapses. ‫تعمل‬ ‫اتصاال‬ ‫ت‬ ‫العوامل‬ ‫العصبیة‬ ‫ا‬ً‫ق‬‫وف‬ ‫لنفس‬ ‫المبادئ‬ ‫التي‬ ‫تحكم‬ ‫المشابك‬ ‫العصبیة‬ . •In a few instances, non-neuronal cells can form synapses with neurons, as occurs ,for example, with taste receptor cells in taste buds on the tongue
  • 41. ‫في‬ ‫حاالت‬ ‫نادرة‬ ، ‫یمكن‬ ‫للخالیا‬ ‫غیر‬ ‫العصبیة‬ ‫تشكیل‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ ‫مع‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫مثل‬ ‫المشابك‬ ‫مع‬ ‫خالیا‬ ‫مستقبالت‬ ‫الذوق‬ ‫في‬ ‫براعم‬ ‫التذوق‬ . Functional Anatomy of Chemical Synapses ‫التشریح‬ ‫الوظیفي‬ ‫للمشابك‬ ‫الكیمیائیة‬ •The possible arrangements in typical neuron-to-neuron synapses are close junctions between the axon terminal of one neuron and the plasma membrane of another neuron . ‫الترتیب‬ ‫النموذجي‬ ‫للمشابك‬ ‫العصبیة‬ ‫للخالیا‬ ‫العصبیة‬ ‫هو‬ ‫االرتباط‬ ‫الوثیق‬ ‫بین‬ ‫نهایة‬ ‫محور‬ ‫عصبون‬ ‫لعصب‬ ‫واحد‬ ‫وغشاء‬ ‫البالزما‬ ‫لخلیة‬ ‫عصبون‬ ‫أخرى‬ . •The first neuron, which transmits signals to the second, is designated the presynaptic neuron ;the second neuron, which receives signals from the first, is referred to as the postsynaptic neuron . ‫ُطلق‬‫ی‬ ‫على‬ ‫العصبون‬ ‫األول‬ ‫الذي‬ ‫ینقل‬ ‫اإلشارات‬ ‫إلى‬ ‫العصبون‬ ‫الثاني‬ ‫اسم‬ ‫العصبون‬ ‫قبل‬ ‫المشبكي‬ ، ‫ویطلق‬ ‫على‬ ‫العصبون‬ ‫الثاني‬ ‫الذي‬ ‫یستقبل‬ ‫اإلشارات‬ ‫من‬ ‫العصبون‬ ‫األول‬ . ‫ُطلق‬‫ی‬ ‫على‬ ‫البطيء‬ ‫اسم‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •Most often the presynaptic neuron's axon terminal forms a synapse with either a dendrite or the cell body of the postsynapcic neuron, in which case the synapses are referred to as axodendritic or axosomatic synapses ,respectively. ‫في‬ ‫معظم‬ ‫الحاالت‬ ، ‫یشكل‬ ‫الجزء‬ ‫المحوري‬ ‫من‬ ‫العصبون‬ ‫قبل‬ ‫المشبكي‬ ‫ا‬ً‫ك‬‫مشاب‬ ‫مع‬ ‫جسم‬ ‫شجیري‬ ‫أو‬ ‫خلیة‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ . ‫تسمى‬ ‫هذه‬ ‫األنواع‬ ‫من‬ ‫نقاط‬ ‫االشتباك‬ ‫العصبي‬ ‫ا‬ ‫لمشابك‬ ‫العصبیة‬ ‫المحوریة‬ ‫والمشابك‬ ‫المحوریة‬ ، ‫على‬ ‫التوالي‬ . •In some cases the presynaptic neuron's axon terminal forms a synapse with the postsynaptic neuron's axon terminal, in which case the synapse is called an axoaxonic synapse ‫في‬ ‫بعض‬ ‫الحاالت‬ ، ‫یشكل‬ ‫ا‬ ‫لجزء‬ ‫المحوري‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ ‫ا‬ً‫ك‬‫مشاب‬ ‫مع‬ ‫طرف‬ ‫محور‬ ‫عصبي‬ ‫من‬ ‫العصبون‬ ‫قبل‬ ‫المشبكي‬ . ‫لهذا‬ ‫النوع‬ ‫من‬ ‫المشبك‬ ، ‫یطلق‬ ‫علیه‬ ‫المشبك‬ ‫المحوري‬ .
  • 42. •In all cases, the axon terminal of the presynaptic neuron releases neurotransmitters into the narrow (30-50 nm) space between the two cells, called the synaptic cleft. ‫في‬ ‫جمیع‬ ‫الحاالت‬ ، ‫تضع‬ ‫المحطات‬ ‫المحوریة‬ ‫للخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكي‬ ‫نواقلها‬ ‫العصبیة‬ ‫في‬ ‫مساحة‬ ‫ضیقة‬ ( 09 ‫إلى‬ 59 ‫نانومتر‬ ) ‫بین‬ ‫خلیتین‬ ‫تسمى‬ - Synaptic ‫شق‬ ‫متشابك‬ ( ‫شق‬ ‫متشابك‬ ) . •Once released into the synaptic cleft, the neurotransmitters diffuse rapidly across the cleft and bind to receptors on the postsynaptic neuron ‫عندما‬ ‫یتم‬ ‫إطالق‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الفضاء‬ ‫المشبكي‬ ‫المشقوق‬ ، ‫فإنها‬ ‫تنتشر‬ ‫بسرعة‬ ‫عبر‬ ‫الشق‬ ‫وفي‬ ‫مستقبالتها‬ ‫المحددة‬ ‫على‬ ‫السطح‬ . ‫ترتبط‬ ‫الخالیا‬ ‫العصب‬ ‫یة‬ ‫بعد‬ ‫المشبكي‬ .
  • 43.
  • 44.
  • 45. The binding of the neurotransmitter to the receptors produces a response in the postsynaptic neuron by a mechanism called signal transduction ‫ینتج‬ ‫ربط‬ ‫الناقالت‬ ‫العصبیة‬ ‫بالمستقبالت‬ ‫استجابة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫بو‬ ‫اسطة‬ ‫آلیة‬ ‫تسمى‬ ‫تحویل‬ ‫اإلشارة‬ . •The axon terminal of the presynaptic neuron contains numerous small, membrane-bound compartments called synaptic vesicles ,which store neurotransmitter molecules . ‫تحتوي‬ ‫المحطة‬ ‫المحوریة‬ ‫للخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكي‬ ‫على‬ ‫عدد‬ ‫ك‬ ‫بیر‬ ‫من‬ ‫الخالیا‬ ‫التي‬ ‫تحتوي‬ ‫على‬ ‫ناقالت‬ ‫عصبیة‬ ‫تسمى‬ ‫الحویصالت‬ ‫المشبكیة‬ . •Most neurotransmitters are synthesized in the cylosol of the axon terminal, where the enzymes for their synthesis are located. ‫تصنع‬ ‫معظم‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الخلیة‬ ‫الخلویة‬ ‫الطرفیة‬ ‫المحور‬ ‫یة‬ ( ‫حیث‬ ‫توجد‬ ‫اإلنزیمات‬ ‫الالزمة‬ ‫للقیام‬ ‫بذلك‬ ) . •After synthesis, neurotransmitters, are actively transported into synaptic vesicles, where they are stored until their eventual release by exocytosis.
  • 47. Voltage-gated sodium and potassium channels are abundant in the membrane of the axon to support the propagation of action potentials down the length of the axon ‫توجد‬ ‫قنوات‬ ‫جه‬ ‫د‬ ‫الصودیوم‬ ‫والبوتاسیوم‬ ‫بكثرة‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫المحوار‬ ‫ویساعد‬ ‫عملها‬ ‫على‬ ‫نقل‬ ‫إمكانات‬ ‫العمل‬ ‫أثناء‬ ‫هو‬ ‫محور‬ ‫عصبي‬ . • But most abundant in the membrane of the axon terminal are voltage-gated calcium channels . ‫ولكن‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫الطرفیة‬ ‫المحوریة‬ ‫یوجد‬ ‫المزید‬ ‫من‬ ‫قنوات‬ ‫جهد‬ ‫الكالسیوم‬ . •These calcium channels open when the axon terminal is depolarized, which occurs upon arrival of an action potential at the axon terminal (see (1) in next Figure). ‫عندما‬ ‫یصل‬ ‫جهد‬ ‫الفعل‬ ‫إلى‬ ‫نهایة‬ ‫المحور‬ ‫العصبي‬ ( ‫ونهایة‬ ‫المحوار‬ ‫غیر‬ ‫مس‬ ‫تقطب‬ ) ، ‫تفتح‬ ‫قنوات‬ ‫الكالسیوم‬ ‫هذه‬ . •When the calcium channels open (2), they allow calcium to flow down its electrochemical gradient into the axon terminal, increasing the concentration of cytosolic calcium in the axon terminal. ‫عندما‬ ‫یتم‬ ‫فتح‬ ‫هذه‬ ‫القنوات‬ ، ‫یتدفق‬ ‫الكالسیوم‬ ‫إلى‬ ‫المحطة‬ ‫المحوریة‬ ً‫ء‬‫بنا‬ ‫على‬ ‫التدرج‬ ‫الكهروكیمیائي‬ ، ‫وتركیز‬ ‫الكالسیوم‬ ‫الخلوي‬ ‫في‬ ‫الطرف‬ ‫یزید‬ ‫المحور‬ ‫العصبي‬ .
  • 48. •Calcium then causes the membranes of synaptic vesicles to fuse with vesicle attachment sites on the inner surface of the axon terminal membrane and undergo exocytosis, thereby releasing the neurotransmitters into the synaptic cleft (3). ‫یقوم‬ ‫الكالسیوم‬ ‫بعد‬ ‫ذلك‬ ‫بدمج‬ ‫أغشیة‬ ‫الحویصالت‬ ‫المشبكیة‬ ‫مع‬ ‫مواقع‬ ‫محددة‬ ‫على‬ ‫السطح‬ ‫الداخلي‬ ‫للغشاء‬ ‫الطرفي‬ ‫للمحور‬ ‫ویحدث‬ ‫خروج‬ ‫الخالیا‬ . ‫وهكذا‬ ، ‫یتم‬ ‫إطالق‬ ‫الن‬ ‫واقل‬ ‫العصبیة‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ . •Unless another action potential arrives, neurotransmitter release stops within a few milliseconds, because the voltage-gated calcium channels close soon after opening, and because calcium ions are actively transported out of the axon terminal on a continual basis, bringing the cytosolic calcium concentration back to its resting level. ‫إذا‬ ‫لم‬ ‫یتم‬ ‫الوصول‬ ‫إلى‬ ‫جهد‬ ‫فعل‬ ، ‫فإن‬ ‫إطالق‬ ‫النواقل‬ ‫العصبیة‬ ‫یتوقف‬ ‫في‬ ‫غضون‬ ‫بضعة‬ ‫أجزاء‬ ‫من‬ ‫األلف‬ ‫من‬ ‫الثانیة‬ ، ‫ألن‬ ‫قنوات‬ ‫الكالسیوم‬ ‫تغلق‬ ‫بسرعة‬ . ‫من‬ ‫ن‬ ‫احیة‬ ‫أخرى‬ ، ‫یتم‬ ‫نقل‬ ‫أیونات‬ ‫الكالسیوم‬ ‫بنشاط‬ ‫خارج‬ ‫المحطة‬ ‫المحوریة‬ ‫ویعود‬ ‫تركیز‬ ‫الكالسیوم‬ ‫في‬ ‫العصارة‬ ‫الخلویة‬ ‫إلى‬ ‫طبیعته‬ . ‫قبل‬ ‫العودة‬ . •A second action potential will elicit a quick burst of neurotransmitter release similar to the first. ‫تتسبب‬ ‫احتمالیة‬ ‫اإلجراء‬ ‫الثاني‬ ‫في‬ ‫اإلطالق‬ ‫المفاجئ‬ ‫للناقالت‬ ‫العصبیة‬ ‫كما‬ ‫كان‬ ‫من‬ ‫قبل‬ . •When a series of action potentials arrives at an axon terminal, the amount of neurotransmitter released from the presynaptic cell is greater than the amount released in response to a single action potential, and as a result the concentration of neurotransmitter in the synaptic cleft increases as the frequency of action potentials increases. ‫عندما‬ ‫تصل‬ ‫سلسلة‬ ‫من‬ ‫إمكانات‬ ‫الفعل‬ ‫إلى‬ ‫المحطة‬ ‫المحوریة‬ ، ‫فإن‬ ‫كمیة‬ ‫الناقالت‬ ‫العصبیة‬ ‫المنبعثة‬ ‫من‬ ‫الخالیا‬ ‫العصب‬ ‫یة‬ ‫قبل‬ ‫المشبكیة‬ ‫تكون‬ ‫أكبر‬ ‫من‬ ‫مجرد‬ ‫یصل‬ ‫إلى‬ ‫جهد‬ ‫فعل‬ ‫واحد‬ ، ‫وبالتالي‬ ‫فإن‬ ‫زیادة‬ ‫تواتر‬ ‫جهد‬ ‫الفعل‬ ‫یزید‬ ‫من‬ ‫تركیز‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ .
  • 49. •Once in the synaptic cleft, neurotransmitter molecules diffuse away from the axon terminal and toward the postsynaptic neuron, where they bind to receptors (see (4) in next figure), thereby inducing a response in the postsynaptic neuron (5) ‫ثم‬ ‫تنتشر‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫وترتبط‬ ‫بمستقبالتها‬ ‫المحددة‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫تكوین‬ ‫الردود‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •The binding of a neurotransmitter molecule to a receptor is a brief and reversible process. ‫یكون‬ ‫اتصال‬ ‫الناقل‬ ‫العصبي‬ ‫بالمستقبل‬ ‫ًا‬‫ی‬‫مقطع‬ ً ‫وقابال‬ ‫لالنعكاس‬ . The neurotransmitter is a ligand and the receptor is a protein, and the two bind through weak chemical interactions ‫الناقل‬ ‫العصبي‬ ‫عبارة‬ ‫عن‬ ‫لیجند‬ ‫والمستقبالت‬ ‫عبارة‬ ‫عن‬ ‫بروتین‬ ، ‫وكالهما‬ ‫یرتبط‬ ‫ببعضهما‬ ‫البعض‬ ‫بروابط‬ ‫كیمیائیة‬ ‫ضعیفة‬ . •If neurotransmitter molecules were to remain indefinitely in the synaptic cleft following their release, they would bind to receptors over and over again, inducing a continual response in the postsynaptic neuron.
  • 50. ‫إذا‬ ‫كانت‬ ‫النواقل‬ ‫العصبیة‬ ‫مرتبطة‬ ‫بشكل‬ ‫دائم‬ ‫ومستمر‬ ‫بالمستقبالت‬ ، ‫فإنها‬ ‫ستثیر‬ ‫استجابة‬ ‫دائمة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ . •However, continual binding does not occur because a number of processes quickly clear the neurotransmitter from the cleft, thereby terminating the signal. ‫ومع‬ ‫ذلك‬ ، ‫ال‬ ‫یحدث‬ ‫هذا‬ ( ‫االتصال‬ ‫الدائم‬ ‫للناقل‬ ‫العصبي‬ ‫بالمستقبالت‬ ) ‫ألن‬ ‫العدید‬ ‫من‬ ‫العملیات‬ ‫تتسبب‬ ‫في‬ ‫إزالة‬ ‫الناقل‬ ‫العصبي‬ ‫بسرعة‬ ‫من‬ ‫الشق‬ ‫المشبكي‬ . •Some neurotransmitter molecules are degraded by enzymes ,which may be located either on the postsynaptic neuron's plasma membrane (see (6) in next figure), on the presynaptic neuron's plasma membrane, on the plasma membranes of nearby glial cells, or even in the cytoplasm of the presynaptic neuron or glial cells . ‫یتم‬ ‫إنتاج‬ ‫بعض‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫بواسطة‬ ‫اإلنزیمات‬ ‫الموجودة‬ ‫في‬ ‫غشاء‬ ‫البالزما‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ ، ‫أو‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ، ‫أو‬ ‫الخالیا‬ ‫الدبقیة‬ ، ‫أو‬ ‫حتى‬ ‫ینهار‬ ‫سیتوبالزم‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكي‬ ‫أو‬ ‫الخالیا‬ ‫الدبقیة‬ . •Other neurotransmitter molecules can be actively transported back into the presynaptic neuron that released them (see (7) in next figure), a process known as reuptake . ‫یتم‬ ‫إرجاع‬ ‫بقیة‬ ‫جزیئا‬ ‫ت‬ ‫الناقل‬ ‫العصبي‬ ‫بنشاط‬ ‫إلى‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبكیة‬ ( ‫آلیة‬ ‫تسمى‬ ‫االسترداد‬ ) . •Once inside the neuron, these neurotransmitter molecules are usually degraded and the breakdown products recycled to form new neurotransmitter molecules . ‫تتحلل‬ ‫النواقل‬ ‫العصب‬ ‫یة‬ ‫بعد‬ ‫دخولها‬ ‫الخلیة‬ ‫وتستخدم‬ ‫نواتج‬ ‫التحلل‬ ‫لصنع‬ ‫جزیئات‬ ‫ناقل‬ ‫عصبي‬ ‫جدیدة‬ . ‫تم‬ ‫وضعه‬ . •Other neurotransmitter molecules in the synaptic cleft simply diffuse out of the cleft (see (8) in next figure) ‫یتم‬ ‫تحریر‬ ‫جزء‬ ‫آخر‬ ‫من‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ ‫عن‬ ‫ط‬ ‫ریق‬ ‫االنتشار‬ ‫البسیط‬ . •So long as neurotransmitter molecules are not bound to receptors, they may be subject to any of the fates just described.
  • 51. ‫تواجه‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫غیر‬ ‫المرتبطة‬ ‫بالمستقبالت‬ ‫أحد‬ ‫المصائر‬ ‫المذكورة‬ ‫أعاله‬ . •As a result, neurotransmitter is usually present in the synaptic cleft for only a few milliseconds after its release from the presynaptic neuron. ‫نتیجة‬ ‫لذلك‬ ، ‫تبقى‬ ‫الناقالت‬ ‫العصبیة‬ ‫في‬ ‫الشق‬ ‫المشبكي‬ ‫لبضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ ‫بعد‬ ‫إطالقها‬ . •It takes approximately 1-5 msec from the time an action potential arrives at the axon terminal before a response occurs in the postsynaptic cell ‫یحدث‬ ‫إطالق‬ ‫النواقل‬ ‫العصبیة‬ ‫من‬ 2 ‫إلى‬ 5 ‫أجزاء‬ ‫من‬ ‫الثانیة‬ ‫بعد‬ ‫وصول‬ ‫جهد‬ ‫الفعل‬ ‫إلى‬ ‫المحطة‬ ‫المحوریة‬ . •This time lag, called the synaptic delay, is mostly due to the time required for calcium to trigger the exocytosis of neurotransmitter. ‫یسمى‬ ‫وقت‬ ‫التأخیر‬ ‫هذا‬ ‫بالتأخیر‬ ‫المشبكي‬ ‫ویرجع‬ ‫ذلك‬ ‫إلى‬ ‫الوقت‬ ‫الالزم‬ ‫لعمل‬ ‫الكالسیوم‬ ‫لبدء‬ ‫إفراز‬ ‫الناقل‬ ‫العصبي‬ . •Once in the synaptic cleft, diffusion of neurotransmitter to the receptor is so rapid as to be negligible. ‫في‬ ‫الشق‬ ‫المشبكي‬ ، ‫ینتشر‬ ‫الناقل‬ ‫العصبي‬ ‫ویرتبط‬ ‫بالمستقبل‬ ‫بسرعة‬ ‫كبیرة‬ ، ‫والوقت‬ ‫الالزم‬ ‫للقیام‬ ‫بذلك‬ ‫ال‬ ‫یكاد‬ ‫یذكر‬ . •Norepinephrine is actively transported back to the pre-synaptic axon ‫یتم‬ ‫نقل‬ ‫النواقل‬ ‫العصبیة‬ ‫مثل‬ norepinephrine ‫بنشاط‬ ‫إلى‬ ‫محور‬ ‫عصبي‬ ‫قبل‬ ‫المشبكي‬ . •CNS neurotransmitters (amines, peptides, amino acids) move into circulation or transported to pre- synaptic terminal. ‫تتدفق‬ ‫الناقالت‬ ‫العصبیة‬ ‫للجهاز‬ ‫العصبي‬ ‫المركزي‬ ( ‫األمینات‬ ‫والببتیدات‬ ‫واألحماض‬ ‫األمینیة‬ ) ‫إلى‬ ‫مجرى‬ ‫الدم‬ ‫أو‬ ‫تنتقل‬ ‫إلى‬ ‫الخلیة‬ ‫قبل‬ ‫المشبكیة‬ .
  • 52.
  • 53. Signal Transduction Mechanisms at Chemical Synapses ‫آلیات‬ ‫إرسال‬ ‫اإلشارات‬ ‫في‬ ‫المشابك‬ ‫الكیمیائیة‬ •The neurotransmitter released by a presynaptic neuron is a messenger ‫الناقل‬ ‫العصبي‬ ‫المنطلق‬ ‫من‬ ‫الخالیا‬ ‫العصبیة‬ ‫قبل‬ ‫المشبك‬ ‫یة‬ ‫لنبي‬ . •When it binds to receptors on the postsynaptic neuron, a message is conveyed. ‫عندما‬ ‫یرتبط‬ ‫هذا‬ ‫الناقل‬ ‫العصبي‬ ‫بمستقبالته‬ ‫في‬ ‫العصبون‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫تنتقل‬ ‫الرسالة‬ ‫ًا‬‫ی‬‫فعل‬ . •Neurotransmitters can induce in a postsynaptic neuron either a fast or a slow response. ‫یمكن‬ ‫أن‬ ‫تحفز‬ ‫الناقالت‬ ‫العصبیة‬ ‫استجابات‬ ‫سریعة‬ ‫أو‬ ‫بطیئة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . Fast response ‫استجابة‬ ‫حادة‬ •Fast response occurs whenever a neurutransmitter binds to a channel-linked receptor ,also called an ionotropic receptor. ‫تحدث‬ ‫اال‬ ‫ستجابة‬ ‫السریعة‬ ‫عندما‬ ‫یتصل‬ ‫ناقل‬ ‫عصبي‬ ‫بمستقبل‬ ‫متصل‬ ‫بالقناة‬ ‫أو‬ ‫مستقبل‬ ‫مؤثر‬ ‫في‬ ‫األیونات‬ . •All channel-linked receptors are ligand-gated channels . ‫جمیع‬ ‫المستقبالت‬ ‫المتصلة‬ ‫بالقناة‬ ‫هي‬ ‫قنوات‬ ‫یجند‬ .
  • 54. •The binding of the neurotransmitter opens the ion channel, allowing a specific ion or ions to permeate the plasma membrane and change the electrical properties of the postsynaptic neuron . ‫یؤدي‬ ‫ارتباط‬ ‫ناقل‬ ‫عصبي‬ ‫إلى‬ ‫فتح‬ ‫القناة‬ ‫األیونیة‬ ‫واختراق‬ ‫أیونات‬ ‫أو‬ ‫أیونات‬ ‫معینة‬ ‫من‬ ‫غشاء‬ ‫البالزما‬ ‫وتغیرات‬ ‫في‬ ‫الخواص‬ ‫الكهربائیة‬ ‫لما‬ ‫بعد‬ ‫یصبح‬ ‫متشابك‬ •The typical response is a change in the membrane potential, called a postsynaptic potential ,or PSP ,which occurs very rapidly and turns off rapidly (normally within a lew milliseconds) because the channel closes as soon as the neuroiransmitter leaves the receptor. ‫تتمثل‬ ‫االستجابة‬ ‫المعتادة‬ ‫في‬ ‫هذه‬ ‫الحالة‬ ‫في‬ ‫إجراء‬ ‫تغییر‬ ‫في‬ ‫إمكانات‬ ‫الغشاء‬ ‫تسمى‬ ‫إمكانات‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫أو‬ PSP ، ‫وهي‬ ‫سریعة‬ ‫ًا‬‫د‬‫ج‬ ‫وشدیدة‬ ‫التحمل‬ . ‫یختفي‬ ‫بسرعة‬ ( ‫في‬ ‫بضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ ) ‫ألن‬ ‫القناة‬ ‫تغلق‬ ‫بسرعة‬ ‫بعد‬ ‫أن‬ ‫ینفصل‬ ‫الناقل‬ ‫العصبي‬ ‫عن‬ ‫المستقبل‬ . Slow responses ‫رد‬ ‫بطيء‬ •Slow responses, on the other hand, are mediated through G-protein-linked receptors called metabotropic receptors ,which include any receptor that works by triggering biochemical changes rather than simply inducing a change in permeability
  • 55. ‫یتم‬ ‫التوسط‬ ‫في‬ ‫االستجابات‬ ‫البطیئة‬ ‫بواسطة‬ ‫مستقبالت‬ ‫البروتین‬ G ( ‫وتسمى‬ ‫ًا‬‫ض‬‫أی‬ ‫مستقبالت‬ ‫التمثیل‬ ‫الغذائي‬ ) ‫تعمل‬ ‫التغییرات‬ ‫البیوكیمیائیة‬ ، ‫ولیس‬ ‫التغییرات‬ ‫البسیطة‬ ‫في‬ ‫نفاذیة‬ ‫الغشاء‬ . •In the nervous system, G proteins can trigger either the opening or the closing of ion channels, depending on the specific synapse . ‫في‬ ‫الجهاز‬ ‫العصبي‬ ، ‫یمكن‬ ‫أن‬ ‫تتسبب‬ ‫بروتینات‬ G ‫في‬ ‫فتح‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ، ‫ًا‬‫د‬‫اعتما‬ ‫على‬ ‫نوع‬ ‫المشبك‬ •These G-protein-regulated ion channels respond to the binding of neurotransmitter more slowly than the channels that mediate the fast response, with durations ranging from milliseconds to hours, depending on the synapse, but with the same ultimate effect : ‫قنوات‬ Y ‫األیونیة‬ ‫التي‬ ‫یتحكم‬ ‫فیها‬ ‫بروتین‬ G ‫أبطأ‬ ‫بكثیر‬ ‫في‬ ‫االرتباط‬ ‫بالناقالت‬ ‫العصبیة‬ ‫من‬ ‫قنوات‬ ‫االستجابة‬ ‫السریعة‬ . ‫أظهر‬ ‫أنه‬ ‫یمكن‬ ‫أن‬ ‫یكون‬ ‫من‬ ‫بضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ ‫إلى‬ ‫بضع‬ ‫ساعات‬ ( ‫حسب‬ ‫نوع‬ ‫المشبك‬ ) ‫لكن‬ ‫تأثیراتها‬ ‫متشابهة‬ ، ‫بما‬ ‫في‬ ‫ذلك‬ : •1-The opening or closing of ion channels alters the permeability of the postsynaptic neuron to a specific ion or ions, resulting in changes in the electrical properties of the cell. •2-The G protein can serve as a direct coupling between the receptor and the ion channel (figure b), or it can trigger the activation or inhibition of a second messenger system (figure c) •3-Neurotransmitters that act through G proteins are also called neuromodulators because some of the slow responses modulate the fast responses occurring at ionotropic receptors. 2. ‫یؤدي‬ ‫فتح‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ‫إلى‬ ‫تغییر‬ ‫في‬ ‫نفاذیة‬ ‫الخالیا‬ ‫ا‬ ‫لعصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫إلى‬ ‫أیونات‬ ‫أو‬ ‫أیونات‬ ‫محددة‬ ، ‫وبالتالي‬ ‫تغیرات‬ ‫في‬ ‫الخصائص‬ ‫تصبح‬ ‫الخلیة‬ ‫كهربائیة‬ . 2. ‫یعمل‬ ‫البروتین‬ G ‫كرابط‬ ‫مباشر‬ ‫بین‬ ‫المستقبل‬ ‫والقناة‬ ‫األیونیة‬ ‫أو‬ ‫یمكنه‬ ‫تنشیط‬ ‫أو‬ ‫تثبیط‬ ‫نظام‬ ‫المرسل‬ ‫الثانوي‬ . ‫عرف‬ُ‫ت‬ ‫الناقالت‬ ‫العصبیة‬ ‫التي‬ ‫تعمل‬ ‫من‬ ‫خالل‬ ‫بروتینات‬ G ‫ًا‬‫ض‬‫أی‬ ‫باسم‬ ‫ِّالت‬‫عد‬ُ‫م‬‫ال‬ ‫العصبیة‬ ‫ألن‬ ‫بعض‬ ‫االستجابات‬ ‫البطیئة‬ ‫تعدل‬ ‫االستجابة‬ . ‫تتولد‬ ‫بسرعة‬ ‫في‬ ‫مستقبالت‬ ‫التأین‬ .
  • 56. Excitatory and inhibitory Synapses ‫المشابك‬ ‫التحفیزیة‬ ‫والمثبطة‬ •In general, a neurotransmitter exerts its effects on a postsynaptic neuron by triggering the opening or closing of ion channels, which typically causes a change in membrane potential.
  • 57. ‫تمارس‬ ‫الناقالت‬ ‫العصبیة‬ ‫ا‬ً‫م‬‫عمو‬ ‫تأثیرها‬ ‫على‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫عن‬ ‫طریق‬ ‫تحفیز‬ ‫فتح‬ ‫أو‬ ‫إغالق‬ ‫القنوات‬ ‫األیونیة‬ ‫التي‬ ‫تغیر‬ ‫إمكانات‬ ‫الغشاء‬ . ‫تطبیق‬ . •Depending on the type of channel that is opened or closed, the resulting change in membrane potential may be positive or negative ;that is, it may cause either a depolarization or a hyperpolarization ,respectively. ‫ًا‬‫د‬‫اعتما‬ ‫على‬ ‫نوع‬ ‫القناة‬ ‫التي‬ ‫تفتح‬ ‫أو‬ ‫غل‬ُ‫ت‬ ‫ق‬ ، ‫قد‬ ‫یكون‬ ‫التغییر‬ ‫في‬ ‫إمكانات‬ ‫الغشاء‬ ‫ًا‬‫ی‬‫إیجاب‬ ‫أو‬ ‫ًا‬‫ی‬‫سلب‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫إزالة‬ ‫االستقطاب‬ ، ‫أو‬ ‫یصبح‬ ‫مفرط‬ ‫االستقطاب‬ . •At any given synapse, the direction of the response is always the same, and the synapse is classified as being either excitatory and inhibitory synapses ‫في‬ ‫المشبك‬ ، ‫یكون‬ ‫اتجاه‬ ‫االستجابة‬ ‫هو‬ ‫نفسه‬ ‫ا‬ً‫م‬‫دائ‬ ، ‫وینقسم‬ ‫المشبك‬ ‫إلى‬ ‫مثیر‬ ‫ومثبط‬ . Excitatory Synapses ‫تحفیز‬ ‫السینابیس‬ •An excitatory synapse is one that brings the membrane potential of the postsynaptic neuron closer to the threshold for generating an action potential; that is, excitatory synapses depolarize the postsynaptic neuron. ‫یخلق‬ ‫المشبك‬ ‫االستثاري‬ ‫إمكانات‬ ‫فعلیة‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ‫ویزیل‬ ‫استقطاب‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •This depolarization is called an excitatory postsynaptic potential, or EPSP, and can occur as either a fast response or a slow response. ‫یسمى‬ ‫هذا‬ ‫االستقطاب‬ ‫بالجهد‬ ‫المثیر‬ ‫لما‬ ‫بعد‬ ‫المشبكي‬ ، ‫أو‬ EPSP ، ‫ویمكن‬ ‫أن‬ ‫یحدث‬ ‫في‬ ‫شكل‬ ‫استجابة‬ ‫بطیئة‬ ‫أو‬ ‫سریعة‬ . Fast EPSPs ‫شارب‬ EPSPs •Fast EPSPs are generally caused by the binding of neurotransmitter molecules to their receptors on the postsynaptic cell, in the process opening channels that allow small cations (sodium and potassium ions) to move through them (Figure a) ً‫ة‬‫عاد‬ ‫ما‬ ‫یكون‬ ‫سبب‬ ‫التهاب‬ ‫العصب‬ ‫البصري‬ ‫الحاد‬ ‫هو‬ ‫ارتباط‬ ‫جزی‬ ‫ئات‬ ‫الناقل‬ ‫العصبي‬ ‫بمستقبالتها‬ ‫المحددة‬ ‫في‬ ‫الخلیة‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ‫وفتح‬ ‫القنوات‬ ‫التي‬ ‫تسمح‬ ‫یحدث‬ ‫االنتقال‬ ‫إلى‬ ‫الكاتیونات‬ ‫الصغیرة‬ (Na ‫و‬ K)
  • 58. •Recall that at resting potential ,sodium is far from equilibrium, and that there is a strong electrochemical force for moving sodium ions into the cell ,whereas because potassium is near equilibrium, only a weak electrochemical force exists for moving potassium ions out of the cell . ‫من‬ ‫المفترض‬ ‫أنه‬ ‫في‬ ‫حالة‬ ‫الراحة‬ ، ‫یكون‬ ‫الصودیوم‬ ‫في‬ ‫حالة‬ ‫عدم‬ ‫توازن‬ ‫ولدیه‬ ‫میل‬ ‫كهروكیمیائي‬ ‫مرتفع‬ ‫ل‬ ‫دخول‬ ‫الخلیة‬ ، ‫بینما‬ ‫البوتاسیوم‬ ‫قریب‬ ‫من‬ ‫التوازن‬ ‫وهناك‬ ‫القلیل‬ ‫من‬ ‫المیل‬ ‫الكهروكیمیائي‬ ‫لمغادرة‬ ‫الخلیة‬ . •Therefore, when channels open, allowing both sodium and potassium ions to move through them, more sodium ions move in than potassium ions move out, producing a net depolarization. ‫لذلك‬ ، ‫عند‬ ‫فتح‬ ‫القنوات‬ ، ‫ُسمح‬‫ی‬ ‫ألیونات‬ K ‫و‬ Na ‫بالمرور‬ ‫عبرها‬ ‫ویدخل‬ ‫المزید‬ ‫من‬ ‫الصودیوم‬ ‫إلى‬ ‫الخلیة‬ ‫بینما‬ ‫أقل‬ ‫من‬ K ‫یترك‬ ‫الخلیة‬ ‫وهذا‬ ‫یسبب‬ ‫نزع‬ ‫االستقطاب‬ . •Note on the voltmeter (oscilloscope) in next Figure that fast EPSPs last only milliseconds. ‫الحظ‬ ‫مقیاس‬ ‫الفولتمیتر‬ ( ‫راسم‬ ‫الذبذبات‬ ) ‫في‬ ‫الشكل‬ ‫أ‬ ‫؛‬ ‫تدوم‬ ESPS ‫السریع‬ ‫فقط‬ ‫بضعة‬ ‫آالف‬ ‫من‬ ‫الثانیة‬ .
  • 59. Slow EPSPs EPSPs ‫بطیئة‬ •Slow EPSPs can be caused by various mechanisms, but a typical mechanism is the closing of potassium channels involving the most common second messenger, cAMP (Figure b) ‫یتم‬ ‫إنتاج‬ EPSPs ‫البطيء‬ ‫بواسطة‬ ‫مجموعة‬ ‫متنوعة‬ ‫من‬ ‫اآللیات‬ ، ‫ولكن‬ ‫اآللیة‬ ‫األكثر‬ ‫ًا‬‫ع‬‫شیو‬ ‫ترجع‬ ‫إلى‬ ‫إغالق‬ ‫قنوات‬ ‫البوتاسیوم‬ ‫بواسطة‬ cAMP ‫المرسال‬ ‫الثانوي‬ . •When the neurotransmittcr binds to a receptor (1) and activates a G protein (2), the G protein then activates the enzyme adenylate cyclasc(3), which then catalyzes the reaction converting ATP to cAMP (4). ‫عندما‬ ‫یتصل‬ ‫ناقل‬ ‫عصبي‬ ‫بالمستقبل‬ ( 2 ) ‫وینشط‬ ‫بروتین‬ G (2) ، ‫ینشط‬ ‫بروتین‬ G ‫إنزیم‬ ‫دورة‬ adenylate 0) ‫وهذا‬ ‫اإلنزیم‬ ‫یحول‬ ATP ‫إلى‬ cAMP) 4) • cAMP acts as a second messenger that activates protein kinase A (5), which catalyzes the addition of a phosphate group to the potassium channel (6). Phosphorylation of the potassium channel closes it (7) cAMP ‫كمرسل‬ ‫ثانوي‬ ‫ینشط‬ ‫بروتین‬ ‫كینا‬ ‫ز‬ ‫أ‬ ( 5 ) ‫الذي‬ ‫یضیف‬ ‫مجموعة‬ ‫فوسفات‬ ‫إلى‬ ‫قناة‬ ‫البوتاسیوم‬ (6) ‫تؤدي‬ ‫الفسفرة‬ ‫في‬ ‫قناة‬ ‫البوتاسیوم‬ ‫إلى‬ ‫إغالقها‬ ) 0 . •Before the potassium channel was phosphorylaled, the channel was open, and potassium ions were leaking out of the cell while sodium ions were leaking into the cell. ‫قبل‬ ‫فسفرة‬ ‫قناة‬ ‫البوتاسیوم‬ ، ‫تكون‬ ‫هذه‬ ‫القناة‬ ‫مفتوحة‬ ، ‫مما‬ ‫یتسبب‬ ‫في‬ ‫تسرب‬ ‫أیونات‬ K ‫ودخول‬ Na ‫إلى‬ ‫الخلیة‬ •No change in membrane potential was occurring because the sodium and potassium leaks were balanced. ‫في‬ ‫هذه‬ ‫الحالة‬ ، ‫ال‬ ‫تتغیر‬ ‫إمكانات‬ ‫الغشاء‬ ‫ألن‬ ‫تسرب‬ K ‫و‬ Na ‫في‬ ‫حالة‬ ‫توازن‬ . • ‫عندما‬ ‫یتم‬ ‫إغالق‬ ‫قناة‬ ‫البوتاسیوم‬ ‫عن‬ ‫طریق‬ ‫الفسفرة‬ ، ‫یتسرب‬ ‫عدد‬ ‫أقل‬ ‫من‬ ‫أیونات‬ ‫البوتاسیوم‬ ‫من‬ ‫الخلیة‬ •The net effect is a depolarization, because if permeability to potassium decreases while permeability to sodium remains the same, the membrane potential will move away from the equilibrium potential for potassium and toward the equilibrium potential for sodium .
  • 60. ‫التأثیر‬ ‫الصافي‬ ‫لهذا‬ ‫هو‬ ‫إزالة‬ ‫االستقطاب‬ ، ‫ألنه‬ ‫عندما‬ ‫تنخفض‬ ‫نفاذیة‬ ‫البوتاسیوم‬ ‫بینما‬ ‫ال‬ ‫تتغیر‬ ‫نفاذیة‬ ‫الصودیوم‬ ، ‫فإن‬ ‫اإلمك‬ ‫انات‬ ‫الغشاء‬ ‫خارج‬ ‫التوازن‬ ‫لـ‬ K ‫ویتحرك‬ ‫نحو‬ ‫توازن‬ ‫الصودیوم‬ •Slow EPSPs take longer to develop and last longer (seconds lo hours) than fast EPSPs. In the case of cAMPdependent closure of potassium channels, the membrane potential will not return to resting conditions until the potassium channels are dephosphorylated, which will not occur until enough cAMP has been degraded by phosphodiesterase to return the cAMP concentration to its resting level. ‫مدة‬ EPSPs ‫بطیئة‬ ‫وطویلة‬ ‫وطویلة‬ ‫األمد‬ ‫ًا‬‫ض‬‫أی‬ ‫طویلة‬ ( ‫بضع‬ ‫ثوان‬ ‫إل‬ ‫ى‬ ‫بضع‬ ‫ساعات‬ ) ، ‫بینما‬ ‫قنوات‬ ‫البوتاسیوم‬ ‫مع‬ ‫یتم‬ ‫إغالق‬ ‫اآللیة‬ ‫المعتمدة‬ ‫على‬ cAMP ، ‫وال‬ ‫تعود‬ ‫إمكانات‬ ‫الغشاء‬ ‫إلى‬ ‫الراحة‬ ‫ما‬ ‫لم‬ ‫یتم‬ ‫إعادة‬ ‫فسفرة‬ ‫قنوات‬ ‫البوتاسیوم‬ ، ‫وهذا‬ ‫یحدث‬ ‫هذا‬ ‫اإلجراء‬ ‫عندما‬ ‫یتحلل‬ cAMP ‫بواسطة‬ ‫إنزیم‬ phosphordiasterase
  • 61. ‫المشابك‬ ‫المثبطة‬ •An inhibitory synapse is one that either takes the membrane potential of the postsynaptic neuron away from the action potential threshold by hyperpolarizing the neuron ,or stabilizes the membrane potential at the resting value . ‫المشبك‬ ‫المثبط‬ ‫هو‬ ‫المشبك‬ ‫الذي‬ ‫یتم‬ ‫منعه‬ ‫عن‬ ‫طریق‬ ‫فرط‬ ‫االستقطاب‬ ‫أو‬ ‫عن‬ ‫طریق‬ ‫الحفاظ‬ ‫على‬ ‫إمكانات‬ ‫عمل‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكیة‬ ‫ثابتة‬ ‫في‬ ‫حالة‬ ‫الراحة‬ . ‫یصبح‬ ‫جهد‬ ‫الفعل‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •In either case, activity at the synapse decreases the likelihood that an action potential will be generated in the postsynaptic nenron (which is why the synapse is said to be inhibitory). ‫في‬ ‫كلتا‬ ‫الحالتین‬ ، ‫یقلل‬ ‫نشاط‬ ‫هذا‬ ‫المشبك‬ ‫من‬ ‫احتمالیة‬ ‫الفعل‬ ‫المحتمل‬ ‫في‬ ‫الخالیا‬ ‫العصبیة‬ ‫بعد‬ ‫المشبكي‬ . •At inhibitory synapses, the binding of a neurotransmitter to its receptors opens channels for either potassium ions or chloride ions. ‫في‬ ‫المشبك‬ ‫المثبط‬ ، ‫یؤدي‬ ‫ارتباط‬ ‫الناقل‬ ‫العصبي‬ ‫بالمستقبالت‬ ‫إلى‬ ‫فتح‬ ‫قنوات‬ ‫ألیونات‬ ‫الكلور‬ ‫والبوتاسیوم‬ . •When a neurotransrnitter causes potassium channels to open, potassium will move out of the cell, hyperpolarizing it . ‫عندما‬ ‫یتسبب‬ ‫الناقل‬ ‫العصبي‬ ‫في‬ ‫فتح‬ ‫القنوات‬ ، ‫یتم‬ ‫إطالق‬ ‫البوتاسیوم‬ ‫من‬ ‫الخلیة‬ ، ‫مما‬ ‫یؤدي‬ ‫إلى‬ ‫فرط‬ ‫استقطاب‬ ‫الخلیة‬ . •This hyperpolarization is called an inhibitory post-synaptic potential ,orIPSP .
  • 62. ‫یسمى‬ ‫هذا‬ ‫االستقطاب‬ ‫المفرط‬ ‫بإمكا‬ ‫نیة‬ ‫تثبیط‬ ‫ما‬ ‫بعد‬ ‫المشبكي‬ ، ‫أو‬ IPSP •An IPSP, like an EPSP, is a graded potential: When more neurotransmitter molecules bind to receptors, more potassium channels open and the hyperpolarization is greater. ‫یتمتع‬ IPSP ، ‫مثل‬ EPSP ، ‫بإمكانیة‬ ‫متدرجة‬ : ‫كلما‬ ‫زاد‬ ‫ارتباط‬ ‫جزیئات‬ ‫الناقل‬ ‫العصبي‬ ‫بالمستقبالت‬ ، ‫زادت‬ ‫القنوا‬ ‫یتم‬ ‫إطالق‬ ‫المزید‬ ‫من‬ ‫البوتاسیوم‬ ‫وسیكون‬ ‫فرط‬ ‫االستقطاب‬ ‫أكثر‬ ‫حدة‬ (‫مثل‬ EPSP) • IPSPs (like EPSPs and all other graded potentials) decrease in size as they move toward the axon hillock, where the hyperpolarization moves the membrane potential away from threshold, thereby decreasing the likelihood that an action potential will be generated in the postsynaptic neuron. ‫بینما‬ ‫نتحرك‬ ‫على‬ ‫طول‬ ‫المحور‬ ‫العصبي‬ ‫إلى‬ ‫سلسلة‬ ‫التالل‬ ‫المحوریة‬ (‫محور‬ hillock axon) ، ‫تنخفض‬ ‫كمیة‬ IPSPs (‫مثل‬ EPSPs)
  • 63. Inhibitory post-synaptic potential involving potassium channels ‫في‬ IPSP ، ‫تشارك‬ ‫قنوات‬ ‫البوتاسیوم‬ •What happens when a neurotransmitter causes chloride (Cl- ) channels to open depends on the size and direction of the electrochemical driving force acting to move chloride ions across the postsynaptic neuron membrane. ‫عندما‬ ‫یتسبب‬ ‫ناقل‬ ‫عصبي‬ ‫في‬ ‫فتح‬ ‫قنوات‬ ‫الكلور‬ ( ‫حسب‬ ‫حجم‬ ‫واتجاه‬ ‫قوة‬ ‫التوصیل‬ ) ‫وعبور‬ ‫أیونات‬ ‫الكلور‬ ‫الغشاء‬ ‫بعد‬ ‫المشبكي‬ ‫تصبح‬ ‫خالیا‬ ‫عصبیة‬ ، ‫ما‬ ‫یحدث‬ . •Because the chloride ion has a negative charge (is an anion), the membrane potential at rest is an electrical force that acts to move chloride out of the cell . ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫أیونات‬ ‫الكلور‬ ‫لها‬ ‫شحنة‬ ‫سالبة‬ ، ‫فإن‬ ‫إمكانات‬ ‫الغشاء‬ ‫في‬ ‫حالة‬ ‫السكون‬ ‫تسبب‬ ‫قوة‬ ‫كهربائیة‬ ‫تمیل‬ ‫إلى‬ ‫طرد‬ ‫أیونات‬ ‫الكلور‬ . ‫من‬ ‫الخلیة‬ ‫یمكن‬ ‫أن‬ ‫یكون‬ •However, because chloride ions are found in greater concentration outside the cell than inside, there is a chemical force for moving chloride into the cell . ‫ومع‬ ‫ذلك‬ ، ‫ا‬ ً‫نظر‬ ‫ألن‬ ‫تركیز‬ ‫أیونات‬ ‫الكلور‬ ‫خارج‬ ‫الخلیة‬ ‫أعلى‬ ‫منه‬ ‫بداخلها‬ ، ‫فهنا‬ ‫ك‬ ‫ًا‬‫ض‬‫أی‬ ‫قوة‬ ‫كیمیائیة‬ ‫لدخول‬ ‫الكلور‬ ‫إلى‬ ‫الخلیة‬ . •The net force depends on the neuron in question. ‫لها‬ ‫قوى‬ ‫نقیة‬ ‫تعتمد‬ ‫على‬ ‫حالة‬ ‫الخالیا‬ ‫العصبیة‬ . • In some neurons, chloride ions are actively transported out of the cell, making the concentration outside much higher than inside the cell. ‫في‬ ‫بعض‬ ‫الخالیا‬ ‫العصبیة‬ ، ‫یتم‬ ‫طرد‬ ‫أیونات‬ ‫الكلور‬ ‫بشكل‬ ‫نشط‬ ‫من‬ ‫الخلیة‬ ، ‫وبالتالي‬ ‫یكون‬ ‫تركیز‬ ‫الكلور‬ ‫خارج‬ ‫الخلیة‬ ‫أعلى‬ ‫بكثیر‬ ‫منه‬ ‫داخل‬ ‫الخلیة‬ . • Under these conditions, the equilibrium potential for chloride is negative and larger than the resting membrane potential. ‫في‬ ‫مثل‬ ‫هذه‬ ‫الحالة‬ ، ‫تكون‬ ‫احتمالیة‬ ‫توازن‬ ‫الكلور‬ ‫سالبة‬ ‫وهي‬ ‫أكبر‬ ‫من‬ ‫احتمالیة‬ ‫الراحة‬ ‫للغشاء‬ . •In other neurons no active transport of chloride occurs, but there are some ion channels through which chloride can diffuse. ‫في‬ ‫بعض‬ ‫ال‬ ‫خالیا‬ ‫العصبیة‬ ‫األخرى‬ ، ‫ال‬ ‫یوجد‬ ‫نقل‬ ‫نشط‬ ‫للكلور‬ ‫وهناك‬ ‫قنوات‬ ‫إلطالق‬ ‫الكلور‬ .