155 PNS -revised on 26-11-2013

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155 PNS -revised on 26-11-2013

  1. 1. PERIPHERAL NERVOUS SYSTEM AND THE SPECIAL SENSES DR. T.C. MATHEW, Kuwait University
  2. 2. MENINGES OF THE BRAIN AND SPINAL CORD The brain and spinal cord is covered by three layers of membranes called the meninges. The outermost membrane is the dura mater. Below the dura is the arachnoid mater. The space that separates these two is called the subdural space. The innermost layer is the pia mater. Between the arachnoid and pia is the subarachnoid space, within which the cerebrospinal fluid circulates. Cerebrospinal fluid (CSF) provides a liquid cushion for the brain and spinal cord. CSF is formed by choroid plexuses in the brain ventricles DR. T.C. MATHEW, Kuwait University
  3. 3. Anatomy of the Spinal Cord DR. T.C. MATHEW, Kuwait University
  4. 4. The Spinal Cord It extends from the medulla oblongata Extends from the foramen magnum to the level of the vertebra L1 or L2 The spinal cord does not extend the entire length of the vertebral column. The spinal cord shows two enlargements. They are the Cervical enlargement (from 4th cervical to the first thoracic vertebra) and Lumbar enlargement (from ninth to the 12th thoracic vertebra) The conical tapering of the spinal cord is called conus medullaris. Conus medullaris – the inferior end of the spinal cord Filum terminale – long filament of connective tissue Attaches to the coccyx inferiorly Cervical and lumbar enlargements Where nerves for upper and lower limbs arise Cauda equina – collection of nerve roots DR. T.C. MATHEW, Kuwait University
  5. 5. Gray Matter of the Spinal Cord and Spinal Roots Shaped like the letter H Gray commissure – contains the central canal Anterior horns – contain cell bodies of motor neurons Posterior horns – consist of interneurons DR. T.C. MATHEW, Kuwait University
  6. 6. Spinal Nerves Posterior View 31 pairs – contain thousands of nerve fibers Connect to the spinal cord Named for point of issue from the spinal cord  8 pairs of cervical nerves (C -C ) 1 8  12 pairs of thoracic nerves (T1T12)  5 pairs of lumbar nerves (L1-L5)  5 pairs of sacral nerves (S1-S5)  1 pair of coccygeal nerves (C0) DR. T.C. MATHEW, Kuwait University
  7. 7. Spinal Nerves The spinal nerve has two major branches. The posterior (dorsal) ramus that innervate the deep muscles and skin of the dorsal surface of the trunk and anterior (ventral) ramus that innervate the muscles and structures of the upper and lower limb and skin of the lateral and ventral surface of the trunk. DR. T.C. MATHEW, Kuwait University
  8. 8. DISTRIBUTION OF SPINAL NERVES AND PLEXUSES Except for spinal nerves T1-T12, the anterior rami do not go direcly to the body structures. Instead they form network by joining the anterior rami of adjacent nerves. A network of such axons is called a plexus. They are: Cervical plexus Brachial plexus Lumbar plexus Sacral plexus Coccygeal plexus DR. T.C. MATHEW, Kuwait University
  9. 9. The Cervical Plexus Formed by ventral rami of first four cervical nerves Most are cutaneous nerves Some innervate muscles of the anterior neck Phrenic nerve – the most important nerve of the cervical plexus DR. T.C. MATHEW, Kuwait University
  10. 10. The Brachial Plexus and Innervation of the Upper Limb Formed by ventral rami of C5-C8 Cords give rise to main nerves of the upper limb DR. T.C. MATHEW, Kuwait University
  11. 11. The Lumbar Plexus and Innervation of the Lower Limb Lumbar plexus Arises from L1-L4 DR. T.C. MATHEW, Kuwait University Smaller branches innervate the posterior abdominal wall and psoas muscle Main branches innervate the anterior thigh Femoral nerve – innervates anterior thigh muscles Obturator nerve – innervates adductor muscles
  12. 12. The Sacral Plexus Arises from spinal nerves L4S4 Caudal to the lumbar plexus Often considered with the lumbar plexus Lumbosacral plexus DR. T.C. MATHEW, Kuwait University
  13. 13. Innervation of the Lower Limb Sciatic nerve – the largest nerve of the sacral plexus Actually two nerves in one sheath Tibial nerve – innervates most of the posterior lower limb Common fibular (peroneal) nerve – innervates muscles of the anterolateral leg DR. T.C. MATHEW, Kuwait University
  14. 14. The Sacral Plexus DR. T.C. MATHEW, Kuwait University
  15. 15. AUTONOMIC NERVOUS SYSTEM (ANS) The ANS is concerned with the innervation of viscera, glands, blood vessels and the heart. Their regulatory actions are considered to be automatic or autonomous. The autonomic nervous system is divided into the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS). DR. T.C. MATHEW, Kuwait University
  16. 16. The Sympathetic Nervous System    The SNS generally excites the nervous system. It increases blood flow to the heart, muscles and brain but decreases functions in the viscera that are not needed for fight or flight. The most common neurotransmitter used by the SNS is norepinephrine. The Parasympathetic Nervous System    The PSNS generally inhibits the nervous system. It has a localized and narrow effect, slows the heart rate and increased intestinal and digestive activities. The most common neurotransmitter used by the PSNS is acetylcholine (ACh). DR. T.C. MATHEW, Kuwait University
  17. 17. The Special Senses Taste, smell, sight, hearing, and balance Touch – actually a large group of general senses Taste – gustation Smell – olfaction Receptors – classified as chemoreceptors Respond to chemicals DR. T.C. MATHEW, Kuwait University
  18. 18. T A H K N U O Y DR. T.C. MATHEW, Kuwait University

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