Nervous System


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Nervous System

  3. 3. An Overview <ul><li>The Nervous System is the body’s information gatherer. storage center, and control System . Its overall function is to collect information about </li></ul><ul><li>the external conditions in relation to the body’s </li></ul><ul><li>internal state, to analyze this information, and </li></ul><ul><li>to initiate appropriate responses to satisfy certain needs ( Maintain Homeostasis ). </li></ul>
  4. 4. <ul><li>It is concerned with the reception of stimuli transmission of impulses, interpretation of sensations and integrations of sensations that arise from both the internal and external environment The most Powerful if these needs is survival. </li></ul>
  5. 5. <ul><li>The nerves do not form one single system, </li></ul><ul><li>but several which are interrelated. Some of these are physically separated, others are different in function only </li></ul>
  6. 6. PARTS OF THE NERVOUS SYSTEM <ul><li>The nervous system is a collection of cells, tissues, and organs. It can be split into two separate divisions: the central nervous system and the peripheral nervous system. </li></ul>
  7. 7. <ul><li>The central nervous system (CNS) acts as the command center of the body. It interprets incoming sensory information, then sends out instructions on how the body should react. </li></ul><ul><li>The brain and spinal cord make up the </li></ul><ul><li>Central Nervous System (CNS ). </li></ul>
  8. 8. <ul><li>The Central Nervous System (CNS ) consist </li></ul><ul><li>of the Brain and the Spinal Cord . The Spinal </li></ul><ul><li>Cord carries messages form the body to the </li></ul><ul><li>brain, where they analyzed and interpreted . Response messages and then </li></ul><ul><li>passes from the Brain through the Spinal </li></ul><ul><li>Cord and to the rest of the body. </li></ul>
  9. 9. THE BRAIN <ul><li>The brain is a large soft mass of nerve tissue that is contained inside a vault of bone called the cranium. It is the cranial portion of the CNS. </li></ul><ul><li>The brain is also called the &quot;encephalon.&quot; The brain is composed of neurons (nerve cells) and neuroglia (supporting nerve cells). The brain consists of gray and white matter. The gray </li></ul><ul><li>matter is nervous tissues of a grayish color that forms an &quot;H&quot; shaped structure and is </li></ul><ul><li>surrounded by white matter. </li></ul>
  10. 10. <ul><li>The human brain has more than 10 billion nerve cells and over 50 billion other cells and now </li></ul><ul><li>weighs on an average of 3 1/8 pounds, where it used to weigh less than 3 pounds. The brain monitors and regulates your unconscious bodily functions like breathing and heart rate, and coordinates most of your voluntary movement. </li></ul><ul><li>It is also the area of consciousness, thought and creativity! </li></ul>
  11. 12. THE SPINAL CORD: <ul><li>The spinal cord is an ovoid column of nervous tissue that averages about 44 cm </li></ul><ul><li>in length when it is flattened out. The </li></ul><ul><li>spinal cord extends from the medulla oblongata in the brain stem to the 2nd lumbar vertebra in the spinal canal. </li></ul>
  12. 13. <ul><li>All of the nerves in your arms, legs and </li></ul><ul><li>trunk originate from the spinal cord. The spinal cord is the center of reflexive action. When you are stimulated in any way, shape or form, there is a reflex arc that goes from the peripheral nerve to the spinal cord, up </li></ul><ul><li>to the brain and back down to relay the action </li></ul>
  13. 14. <ul><li>The spinal cord is housed in a vertebral (bony) vault for its own protection. The spinal cord travels down through a hole in each vertebrae. If you were to see the spinal cord </li></ul><ul><li>in a cross-section, you would notice that it does not fill </li></ul><ul><li>the vertebral space in the vertebral column, it is </li></ul><ul><li>surrounded by other tissue (pia mater), cerebrospinal </li></ul><ul><li>fluid (CSF), another tissue (arachnoid mater), and still another tissue (dura mater). The three types of mater are called the meninges. The meninges also surround the brain. Hence the word &quot;meningitis&quot; when there is an inflammation of the meninges or membranes of the </li></ul><ul><li>spinal cord or brain. </li></ul>
  14. 15. Spinal Nerves <ul><li>Thirty-one pairs of spinal nerves originate from the spinal cord. They are all mixed nerves, and they provide a two-way communication system between the spinal cord and parts of the arms, legs, neck and trunk of the body. </li></ul>
  15. 16. <ul><li>there are eight pairs of &quot;cervical nerves&quot; (numbered C1 - C8), twelve pairs of &quot;thoracic nerves&quot; (T1 - T12), five pairs of &quot;lumbar </li></ul><ul><li>nerves&quot; (L1 - L5), five pairs of &quot;sacral nerves&quot; </li></ul><ul><li>(S1 - S5), and one pair of &quot;coccygeal nerves&quot; </li></ul>
  16. 17. <ul><li>the Peripheral Nervous System (PNS) consists of the neurons NOT included in the Brain and Spinal Cord. Some Peripheral Neurons collect information from the body .and transmit it TOWARD the CNS. These are called AFFERENT NEURONS . Other Peripheral neurons transmit information AWAY from the CNS. These are called EFFERENT NEURONS. </li></ul>
  17. 18. <ul><li>The Peripheral Nervous System (PNS) </li></ul><ul><li>is responsible for the body functions which </li></ul><ul><li>are NOT Under conscious control- like the heartbeat or the digestive system. </li></ul>
  18. 19. The peripheral nervous system (PNS) <ul><li>is the part of the nervous system outside of </li></ul><ul><li>the CNS. It consists mainly of nerves that </li></ul><ul><li>extend from the brain and spinal cord to areas </li></ul><ul><li>in the rest of the body. Cranial nerves carry impulses to and from the brain while spinal nerves carry impulses to and from the spinal cord. </li></ul>
  19. 20. The PNS can be divided into two systems: <ul><li>the somatic nervous system and the </li></ul><ul><li>autonomic nervous system. </li></ul>
  20. 21. <ul><li>The somatic nervous system controls the voluntary movements of the skeletal muscles. The autonomic nervous system control </li></ul><ul><li>activities in the body that are involuntary or automatic. </li></ul>
  21. 22. <ul><li>These include the actions of the heart, </li></ul><ul><li>glands, and digestive organs and associated </li></ul><ul><li>parts. </li></ul>
  22. 23. The autonomic nervous system can be divided further into two subdivisions: <ul><li>the parasympathetic and sympathetic nervous systems. These two subdivisions work against each other. The parasympathetic nervous </li></ul><ul><li>system regulates involuntary activities that </li></ul><ul><li>keep the body running smoothly under </li></ul><ul><li>normal, everyday conditions. The sympathetic nervous system controls involuntary activities that help the body respond to stressful situations. </li></ul>
  23. 25. <ul><li>The smooth Operation of the Peripheral Nervous System is achieved by dividing it </li></ul><ul><li>into Sympathetic And Parasympahatetic Systems . These are opposing actions and </li></ul><ul><li>check on each other to provide balance </li></ul>
  24. 26. <ul><li>The nervous system uses electrical impulses, which travel along the length of the cells (Neurons). The cell processes information from the sensory nerves and initiates an action within milliseconds. </li></ul>
  25. 27. <ul><li>These impulses can travel at up to 250 miles per hour, while the other system such as the Endocrine System may take many hours to response with hormones. </li></ul>
  26. 28. Nervous System Central Nervous System Peripheral Nervous System Motor Nerves Sensory Nerves Somatic Nervous System Autonomic Nervous System Sympathetic Nervous System Parasympathetic Nervous System
  27. 29. The nervous system sorts and interprets incoming information before directing a response. <ul><li>Receptors in the skin sense a tap or other stimulus. </li></ul><ul><li>Sensory neurons transmits the touch message. </li></ul><ul><li>The message is interpreted. A response is sent to the motor neurons. </li></ul><ul><li>Motor neurons transmit a response message to the shoulder muscles. </li></ul><ul><li>The neck muscles are activated, causing the head to turn. </li></ul>
  28. 30. INTRODUCTION <ul><li>Communication is vital to the survival of the living organisms. </li></ul><ul><li>To interact with their environment, multicellular organisms have developed a communication system at the Cellular Level. </li></ul><ul><li>Specialized Cells (Neurons) allow Message to be carried from one to cell to another so that communication among all body parts is smooth and efficient. </li></ul>
  29. 31. <ul><li>In HUMANS , these Cells called NEURONS make up the Nervous System. </li></ul><ul><li>The Nervous System CONTROL S and COORDINATES ALL ESSENTIAL FUNCTIONS of the Human Body. </li></ul><ul><li>The Nervous System RECEIVES and RELAYS information about activities within thee body and Monitors and Responds to INTERNAL and EXTERNAL CHANGES. </li></ul>
  30. 32. Neurons <ul><li>The cells making up the brain, spinal cord, and nerves are called neurons. They are special cells capable of receiving a stimulus (nerve or electrical impulse), transmitting that stimulus throughout their length, and then delivering that stimulus to other cells next to them. The human body contains about 200 billion neurons. Almost half of them are located in the brain. </li></ul>
  31. 33. Neurons <ul><li>The CELLS that carry messages throughout the Nervous System are called NEURONS. </li></ul><ul><li>The Neurons is the basic functional unit of the Nervous System. </li></ul>
  32. 34. The brain and the spinal cord are the two major parts of the central nervous system, or CNS.
  33. 35. THE ANATOMY OF NEURON <ul><li>6. A Neuron consists of THREE MAIN PARTS: </li></ul><ul><li>A. CELL BODY – The largest part, contains the nucleus and much of the cytoplasm ( area between the nucleus and the cell membrane ), most of the metabolic activity of the cell, including the generation of ATP (Adenine Triphosphate - compound that stores energy ) and synthesis of protein. </li></ul><ul><li>B . DENDRITES – Short branch extensions spreading out from the cell body. Dendrites receive STIMULUS ( action potentials ) and carry IMPULSES from the ENVIRONMENT or from the other NEURON S and CARRY THEM TOWARD THE CELL BODY.. </li></ul><ul><li>C. AXON – A long fiber that CARRIES IMPULSES AWAY FROM THE CELL BODY . Each neuron has only ONE AXON . The AXON ends in a series of small swellings called AXON TERMINALS. </li></ul>
  34. 36. <ul><li>. Neurons may have dozens or even hundreds of DENDRITES but usually ONLY ONE AXON. </li></ul><ul><li>8. The axon of most neurons are covered with a lipid layer known as the MYELIN SHEATH. </li></ul><ul><li>9. The Myelin Sheath both insulates and speeds up transmission of action potentials through the axon. </li></ul><ul><li>10. In the Peripheral Nervous System, Myelin is produced by SCHWANN CELLS , which surrounds the axon. </li></ul><ul><li>11. GAPS ( NODES ) in the Myelin Sheath along the length of the axon are known as the NODES OF RANVIER. </li></ul>
  35. 40. SUPPORTING CELLS <ul><li>Neuroglia, or glial cells, are cells that surround neurons in the central nervous system. They do not conduct impulses, but help to support and protect neurons, combining with them to form what is known as nerve tissue. </li></ul>
  36. 41. <ul><li>They also supply neurons with nutrients and remove their wastes. Neuroglia are abundant, accounting for some ten times the number of neurons. An example of neuroglia in the CNS are oligodendrocytes. </li></ul>
  37. 42. <ul><li>In the PNS, neurons are supported by Schwann cells and satellite cells (which form around the cell body to protect and cushion it). </li></ul>
  38. 43. Nerves <ul><li>A nerve is a bundle of axons in the PNS. Each axon or nerve fiber is wrapped in delicate connective tissue. Groups of axons are then bound in coarser connective tissue to form bundles. Finally, many bundles are bound together (along with blood vessels to nourish the axons and Schwann cells) by even tougher connective tissue to form a nerve. </li></ul>
  39. 44. <ul><li>Nerves are categorized like neurons according to the direction in which they conduct impulses. Sensory nerves, made of the axons of sensory neurons, carry impulses to the brain and spinal cord. </li></ul>
  40. 45. <ul><li>Motor nerves, made of the axons of motor neurons, carry impulses to the muscles and glands. Mixed nerves contain axons of both sensory and motor neurons. The most abundant nerves, mixed nerves can conduct impulses both to and from the central nervous system. </li></ul>
  41. 46. The brain <ul><li>The human brain is a soft, shiny, grayish white, mushroom-shaped structure encased within the skull. At birth, a typical human brain weighs between 12 and 14 ounces (350 and 400 grams). By the time an average person reaches adulthood, the brain weighs about 3 pounds (1.36 kilograms). </li></ul>
  42. 47. <ul><li>Because of greater average body size, the brains of male are generally about 10 percent larger than those of females. Although brain size varies considerably among humans, there is no correlation or link between brain size and intelligence. </li></ul>
  43. 48. <ul><li>The human brain is composed of up to one trillion nerve cells. One hundred billion of these are neurons, and the remainder are the supporting neuroglia. The brain consists of gray and white matter. Gray matter is nerve tissue in the CNS composed of neuron cell bodies, neuroglia, and unmyelinated axons; white matter is nerve tissue in the CNS composed chiefly of bundles of myelinated axons. </li></ul>
  44. 49. <ul><li>The brain is protected by the skull and by three membranes called the meninges. The outermost membrane is known as the dura mater, the middle as the arachnoid, and the innermost as the pia mater. Also protecting the brain is cerebrospinal fluid, a liquid that circulates between the arachnoid and pia matter. </li></ul>
  45. 50. <ul><li>The Nervous System has FOUR FUNCTIONS that enable the body to respond quickly. The Nervous System: </li></ul><ul><ul><li>A. Gathers information both from the outside word and from inside the body – SENSORY FUNCTION . </li></ul></ul><ul><ul><li>B. Transmits the information to the processing area of the brain and spinal cord . </li></ul></ul>
  46. 51. <ul><ul><li>C. Processes the information to determine the best response – INTEGRATIVE FUNCTION . </li></ul></ul><ul><ul><li>D. Sends information to the muscle, glands, and organs ( effectors ) so they can respond correctly. Muscular contraction or glandular secretion – MOTOR FUNCTION </li></ul></ul><ul><li>8 9. The Functioning Nervous System is an enormous network of “ one- way streets “. </li></ul>
  47. 52. TRANMISSION OF NERVE IMPULSES <ul><li>The Italian scientist LUIGI GALVANI found that nervous tissue ( group of cells that conduct impulses ) display Electrical Activity in the form of Nerve Impulse, which is a flow of electrical charges along The Cell Membrane of a neuron. </li></ul><ul><li>This Electrical Activity is due to Movement of IONS ( charge particles ) across the Cell Membrane. SODIUM – Na+, and POTASSIUM – K+. </li></ul><ul><li>The movement of theses IONS is affected by their ability to pass through the Cell Membrane , their concentration inside and out of the cell and their charge. </li></ul><ul><li>Neurons have an electrical charge different from the extracurricular Fluid that surrounds them. A difference in electrical charge between two locations called POTENTIALS. </li></ul>
  48. 53. RESTING POTENTIALS <ul><li>1. A Nerve Cell has ELECTRICAL POTENTIAL across its cell membrane because of a difference in the number positively and negatively charge IONS on each side of the Cell Membrane. </li></ul><ul><li>2. The electrical potential is due to PROTEINS in the neuron known as Sodium- Potassium Pumps move Sodium ions (Na+) OUT of the Cell and Actively Pumps Potassium ions (K+) INTO the cell. </li></ul><ul><li>3. The result of this active transport of ions in the cytoplasm of the neuron contains MORE K+ IONS and FEWER Na+ IONS than the surrounding medium. </li></ul><ul><li>4. The Cytoplasm also contains many NEGATIVE CHARGE PROTEINS Molecules and Ions. </li></ul><ul><li>5. K+ ions can leak out across the membrane more easily than Na+ ions can leak in. </li></ul>
  49. 54. <ul><li>6. The Negatively charge protein molecules and ions do not leak in or out. </li></ul><ul><li>7. The Net Result of the leakage of positively charge ions out of the cell is a Negatively charge on the inside of the neuron’s Cell Membrane. </li></ul><ul><li>8. The charge difference is known as the RESTING POTENTIAL of the Neuron’s Cell Membrane. </li></ul><ul><li>9. As a result of its Resting Potentials, the Neuron is said to be POLARAIZED. </li></ul><ul><li>10. POLARIZED – Negatively charge on the inside of the Cell Membrane, and Positively charge on the outside. </li></ul><ul><li>11. A neuron maintains this polarization until it is stimulated. </li></ul><ul><li>12. A STIMULUS is a change in the environment that may be sufficient strength to initiate the impulse. </li></ul><ul><li>13. The ability of a neuron to respond to a stimulus and convert it into a nerve impulse is known as EXCITABILITY. </li></ul>
  50. 55. THE MOVING IMPULSE <ul><li>A Nerve impulse causes a movement of ions across the cell membrane of a neuron. Similar to a riffle passing along the surface of a pond. </li></ul><ul><li>The cell membrane of a neuron contains thousands of tiny molecules known as GATES. ( Sodium and Potassium ). </li></ul><ul><li>These GATES allow either sodium or potassium ions to pass through. </li></ul><ul><li>Generally, the Gates on a neuron are CLOSED. </li></ul><ul><li>A Nerve Impulse STARTS when pressure or other sensory inputs, disturbs a neuron’s Plasma Membrane, causing Sodium Gates to OPEN. </li></ul><ul><li>At the beginning of the impulse, the sodium gates OPEN, allowing positively charge Na+ ions to flow INSIDE the Cell Membrane. </li></ul><ul><li>The INSIDE of the membrane temporarily becomes MORE POSITIVE than the OUTSIDE . This is called DEPOLARIZED. </li></ul><ul><li>The membrane is now said to be DEPOLARIZED ; the charge inside the axon change from negative to positive as sodium ions enter the interior. </li></ul><ul><li>As the impulses passes, the potassium gates OPEN , allowing positively charge K+ ions to FLOW OUT . REPOLARIZED : the inside of the axon resumes a negative charge. </li></ul>
  51. 56. <ul><li>10. The membrane is now said to be REPOLARIZED . Once again NEGATIVELY charge on the INSIDE and POSITIVELY charges on the OUTSIDE. </li></ul><ul><li>11. The DEPOLARIZATION and REPOLARIZATION of a Neuron Membrane is called an ACTION POTENTIAL . Action Potential is another name for a Nerve Impulse or simply an impulse. </li></ul><ul><li>12. After a nerve impulse period, the neuron is unable to conduct a nerve impulse called the REFRACTORY PERIOD. </li></ul><ul><li>13. The REFRATORY PERIOD is very short period during which the sodium- potassium pump continues to return sodium ions to the outside and potassium ions to the inside of the axon . Thus, returning the neuron to RESTING POTENTIALS. </li></ul><ul><li>14. An Impulse is not an electric current , it is a wave of Depolarization and Repolarization. Or a nerve impulse is actually the movement of an action potential along a neuron as a series of voltage-gated ions channels open and close. </li></ul><ul><li>15. An Impulse is much SLOWER than an electric current. </li></ul><ul><li>16. Unlike electric current, the STRENGTH of an Impulse is always the same. </li></ul><ul><li>17. There is either an Impulse to a stimulus or there is not. (ALL-OR-NOTHING PRINCIPLE). </li></ul>
  52. 57. PROPAGATION <ul><li>An impulse is self-propagating. Once started, it continues, </li></ul><ul><li>and moves only in one direction. Like the falling of </li></ul><ul><li>Dominos. </li></ul>
  53. 58. MYELIN SHEATH <ul><li>Myelin Sheaths greatly increase the speed of impulse along an axon. </li></ul><ul><li>Myelin is composed of 80% lipid and 20% protein. </li></ul><ul><li>Myelin is made of specials cells called Schwann Cells that forms an insulated sheath , or wrapping around he axon. </li></ul><ul><li>There are SMALL NODE or GAPS called the NODES OF RANVIER between adjacent myelin sheath cells along the axon </li></ul><ul><li>As an impulse moves down a myelinated ( covered with myelin ) axon , the impulse jumps to form Node to Node instead of moving along the membrane. </li></ul><ul><li>The jumping from Node to Node greatly increase the speed of the impulse. </li></ul><ul><li>Some myelinated axons conduct impulses as rapid as 200 meter per second . </li></ul><ul><li>The formation of the myelin around axons can be thought of as a crucial event in evolution of vertebrates. </li></ul><ul><li>Destruction of large patches of myelin characterized a diseases called MULTIPLE SCLEROSIS . In multiple sclerosis, small and hard plaques appear throughout the myelin. Normal nerve function is impaired, causing symptoms such as double vision, muscular weakness, loss of memory and paralysis. </li></ul>
  54. 59. THE THRESHOLD <ul><li>The strength of the impulse is always the SAME. </li></ul><ul><li>Either there is an impulse in response to a STIMULUS or there is not. </li></ul><ul><li>A STIMULUS must be of adequate strength to cause a neuron to conduct an impulse. </li></ul><ul><li>The MINIMUM LEVEL of a STIMULUS that is REQUIRED to activate a neuron is called the THRESHOLD. </li></ul><ul><li>Any stimulus WEAKER than the THRESHOLD will produce NO impulse. </li></ul><ul><li>Any stimulus STRONGER than the THRESHOLD will produce an impulse. </li></ul><ul><li>A nerve impulse follows the ALL-OR-NONE Principle. </li></ul>
  55. 60. THE SYNAPTIC CLEFT OR SYNAPSE <ul><li>The axon ends with many small swellings called AXON TERMINALS. </li></ul><ul><li>At these terminals the neuron may make contact with the dendrites of another neuron, with a RECEPTOR , or with an EFFECTOR. </li></ul><ul><li>RECEPTORS are special SENSORY NEURONS in SENSE ORGANS that RECEIVE stimuli from the EXTERNAL ENVIRONMENT </li></ul><ul><li>EFFECRTORS are MUSCLES and GLAND S that bring about a COORDINATE RESPONSE. </li></ul>
  56. 61. <ul><li>5. The point of contact at which impulses are passed from one cell to another are known as SYNAPTIC CLEFT OR SYNAPSE. </li></ul><ul><li>6. Neurons that transmit impulses to other neurons DO NOT actually touch one another. The small gap or space between the axon of one neuron and the dendrites or cell body on the next neuron is called the SYNAPSE . One important of the presence of the synapse is that they ensures one-way transmission of impulses in a living person. A nerve impulse CANNOT go backward across a Synapse. </li></ul><ul><li>The axon terminals at a synapse contain tiny vesicles, or sacs. </li></ul><ul><li>These tiny vesicles are filled with CHEMICALS known as NEUROTRANSMITTERS ( Acetylcholine ). </li></ul><ul><li>A NEUROTRANSMITTER is a chemical substance that is used by one neuron to signal another . The impulse is changed from ELECTIRCAL IMPULSE to CHEMICAL IMPULSE ( Electrochemical Impulses ). </li></ul><ul><li>When an impulse reaches the axon terminal, dozen of vesicles fuse with the cell membrane and discharge the NEUROTRANSMITTER into the Synaptic Cleft ( GAP ). </li></ul>
  57. 62. <ul><li>The molecules of the neurotransmitter diffuse across the gap and attach themselves to SPECIAL RECEPTORS on the membrane of the neuron receiving impulse. </li></ul><ul><li>When the neurotransmitter becomes attached to the cell membrane of the adjacent nerve cells, it changes the permeability of that membrane. </li></ul><ul><li>As a result, Na+ ions diffuse through the membrane into the cell. </li></ul><ul><li>If enough transmitter is released by the axon terminal, so many Na+ ions diffuse into the neuron, and that the neuron becomes POLARIZED. </li></ul><ul><li>DEPOLARIZED – inside the membrane becomes more positive than outside. </li></ul><ul><li>This causes a THRESHOLD to be REACHED and an impulse ( ACTION POTENTIAL ) begins in the second cell. </li></ul><ul><li>After the neurotransmitter relays its message, it is rapidly REMOVED or DESTROYED , thus halting it effect. </li></ul><ul><li>The molecules of the neurotransmitter may be broken down by ENZYMES , taken up again by the axon terminal and recycled, or they may simply diffuse away. </li></ul>
  58. 63. <ul><li>19. Synapses are the slowest part of nervous system . The advantage to have many neurons, with gaps between them, is that we can control and received information from different parts of the body at different times . They also ensure one-way transmission of impulses in a living person. </li></ul><ul><li>20. NERVE GAS prevents enzymes from breaking down neurotransmitters, as a result, muscles in the respiratory and nervous system becomes paralyzed. </li></ul>