Slide 1:The Nervous System Dr. Mohammad Bahgat (1430 – 1431 H)


Objectives :Objectives By the end of this lecture, you are expected to: 1- Know the anatomical and functional divisions of the nervous system. 2- Know the general structure of the neuron and central nervous system. 3- Know the composition of the peripheral nervous system. 4- Know the structure of the spinal nerves and understand their communication with the sympathetic nervous system. 5. Understand the segmental innervation of the skin and the skeletal muscles and their clinical application during examination of the patient (some tendon reflexes & testing skin sensation)


Divisions :Divisions - Anatomically, the nervous system can be divided into: 1) Central nervous system: (brain and spinal cord). 2) Peripheral Nervous system: - 12 pairs of cranial nerves. - 31 pairs of spinal nerves. - 2 Sympathetic trunks. - Functionally the nervous system can be divided into: 1) Somatic nervous system: Controls voluntary activities. 2) Autonomic nervous system: Controls involuntary activities.


Slide 4:Dr. Bahgat Central nervous system Consists of Brain & Spinal cord The peripheral nervous system Consists of Cranial nerves Spinal nerves & sympathetic trunks Anatomical divisions of the nervous system


Slide 5:Dr. Bahgat Cell body Dentrites Axon (nerve fiber) The nerve cell (neuron) Consists of & 2 types of processes The nervous system consists of nerve cells or neurons


The central nervous system :The central nervous system - It consists of the brain and spinal cord. - The brain and spinal cord consist of aggregation of large numbers of nerve cells and their processes, supported by specialized tissue called neuroglia. - The nerve cell consists of a cell body and cell processes. - A nerve cell (including its all processes) is called neuron. The neuron has two types of processes: 1) Dendrites: are short processes of the cell body. 2) An axon: is the longest process of the nerve cell (the axon is called the nerve fiber).


Slide 7:Dr. Bahgat Peripheral white matter The spinal cord consists of Structure of the spinal cord (transverse section) Central grey matter Posterior Anterior


Slide 8:Dr. Bahgat Anterior grey horn consists of Grey matter of the spinal cord The grey matter consists of Motor neurons Posterior grey horn consists of Sensory neurons Intermediate grey matter consists of autonomic neurons Posterior Anterior


Slide 9:Dr. Bahgat Grey matter of the spinal cord Posterior horn Anterior horn Intermediate grey matter Posterior Anterior


The central nervous system :The central nervous system The interior of the central nervous system is organized into: 1) Gray matter: consists of the bodies of neurons embedded in neuroglia. 2) White matter: consists of nerve fibers (axons) embedded in neuroglia. - The gray matter of the spinal cord Is divided into: 1) Anterior gray horn: Consists of motor neurons. 2) Posterior gray horn: Consists of sensory neurons. 3) Intermediate gray matter: Consists of autonomic neurons.


Peripheral Nervous System :Peripheral Nervous System It consists of I- cranial nerves and their associated ganglia. II- spinal nerves and their associated ganglia. III- The sympathetic trunks.


Slide 12:Dr. Bahgat 1 2 3 4 5 6 7 8 9 10 11 12 The cranial nerves 1- Olfactory nerve 2- Optic nerve 3- Oculomotor nerve 4- Trochlear nerve 5- Trigeminal nerve 6- Abducent nerve 8- Auditory nerve 7- Facial nerve 10- Vagus nerve 9- Glossopharyngeal N 12- Hypoglossal Nerve 11- Accessory N


I- Cranial nerves :I- Cranial nerves - There are 12 pairs of cranial nerves. - All originate from the brain inside the skull. - They pass through the foramina of the skull to reach the structures they supply. - All terminate in the head and neck except the 10th cranial nerve (vagus) which supplies also structures in the thorax and abdomen.


II- Spinal nerves :II- Spinal nerves - There are 31 spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and one coccygeal.


II- Structure of Spinal nerves :II- Structure of Spinal nerves - Each spinal nerve (except the first) originates from the spinal cord by two roots, anterior (motor) and posterior (sensory) roots - The first cervical nerve has only an anterior (motor) root, and has no posterior (sensory) root.


Slide 16:Dr. Bahgat Anterior motor root Posterior sensory root Structure of the spinal nerve


Slide 17:Dr. Bahgat Posterior Anterior Each spinal nerve consists of Anterior root Posterior root & has a swelling called Posterior root ganglion The 2 roots unite to form Nerve trunk motor fibers Consisted of sensory fibers Consisted of Consisted of both & motor fibers sensory fibers And Structure of the spinal nerve containing Bodies of sensory neurons


Slide 18:Dr. Bahgat Posterior Anterior Each trunk divides into Ventral ramus Consisted of both & motor fibers sensory fibers Dorsal ramus Consisted of both & motor fibers sensory fibers And Structure of the spinal nerve


Slide 19:Dr. Bahgat Structure of the spinal nerve Each spinal nerve consists of Anterior motor root Posterior sensory root Which has a swelling called Posterior root ganglion The 2 roots unite to form Nerve trunk (mixed) Anterior


Slide 20:Dr. Bahgat Structure of the spinal nerve Ventral ramus (mixed) Each trunk divides into & dorsal ramus (mixed) Nerve trunk (mixed) Anterior


II- Structure of the spinal nerves :II- Structure of the spinal nerves - The motor root contains axons of the motor neurons of the anterior gray horn of the spinal cord. - The sensory root consists of central processes (axons) of the neurons of the posterior root ganglion (sensory neurons) and terminates on the sensory neurons of the posterior gray horn of the spinal cord.


II- Structure of the spinal nerves :II- Structure of the spinal nerves - The motor and sensory roots of each spinal nerve unit to form a short nerve trunk. - The nerve trunk is mixed containing both motor and sensory fibers. - Each nerve trunk divides into two rami (branches): 1) Ventral (anterior) ramus. 2) Dorsal (posterior) ramus.


Slide 23:Dr. Bahgat Course of sympathetic efferent Preganglionic fibers The cell bodies of the preganglionic neurones are located in the intermediate gray matter (lateral horn) of all thoracic and upper 2 lumbar segments Pathway of the preganglionic fibers The axons of these cells (myelinated fibers) pass through the anterior gray horn the anterior roots trunks and ventral rami of all thoracic and upper 2 lumbar nerves Posterior


Slide 24:Dr. Bahgat Course of sympathetic efferent They reach the sympathetic chain through communications called white rami communicants To terminate on The postganglionic neurons Preganglionic fibers Posterior


Slide 25:Dr. Bahgat Grey rami communicants Course of sympathetic efferent Postganglionic fibers The cell bodies of the postganglionic neurons are located in All sympathetic ganglia of the 2 sympathetic trunks Each chain carries ganglia corresponding to and connected with all spinal nerves ventral rami through the nonmyelinated Posterior


Slide 26:Dr. Bahgat Grey rami communicants Course of sympathetic efferent Pathway of the postganglionic fibers The axons of these cells (non-myelinated fibers) pass through To reach All spinal ventral rami divide into 2 branches 1- Anterior branch passes through 2- Posterior branch on reaching the corresponding spinal nerve ventral ramus passes backwards through the ventral ramus the ventral then the dorsal ramus The postganglionic fibers Posterior


II- Spinal nerves (continued) :II- Spinal nerves (continued) 1) Ventral (anterior) ramus: - It is mixed (motor and sensory). - The ventral rami supply the skin and muscles of : The trunk (anterior and lateral aspects). The upper and lower limbs. - Each ventral ramus is connected to the sympathetic chain by gray rami communicants and the thoracic and upper two lumbar are also connected to the sympathetic chain by white rami communicants. - The ventral rami unite together to form regional plexuses (except in the thoracic region).


Slide 28:Dr. Bahgat


II- Spinal nerves (continued) :II- Spinal nerves (continued) The ventral rami of the cervical nerves form the cervical and brachial plexuses. The ventral rami of the lumbar nerves form the lumbar plexus and share in the formation of the lumbosacral plexus. The ventral rami of the sacral nerves share in the formation of lumbosacral and coccygeal plexuses. The ventral ramus of the coccygeal nerve shares in the formation of the coccygeal plexus. Within the plexuses, the ventral rami which supply the limbs divide into anterior and posterior divisions to supply the anterior and posterior aspects of the limbs respectively.


II- Spinal nerves (continued) :II- Spinal nerves (continued) 2) The dorsal ramus is also mixed and containing both motor and sensory fibers. - The dorsal rami supply the skin and muscles of the back. - The dorsal rami remain separate (no union) and do not form plexuses. - Each dorsal ramus divides into medial and lateral branches.


Slide 31:Dr. Bahgat Each dorsal ramus divides into medial branch and lateral branch Dorsal rami of spinal nerves Ventral ramus Dorsal ramus Posterior Anterior


Segmental innervations of the skin :Segmental innervations of the skin - The area of skin supplied by a single spinal nerve (single spinal segment) is called a dermatome. - On the trunk, there is considerable overlap between adjacent dermatomes so that no loss of sensation result from damage of only one spinal cord segment. - To produce a region of complete anesthesia, at least three contiguous (adjacent) spinal cord segments (or spinal nerve roots) must be sectioned or damaged.


Slide 33:Dr. Bahgat Dermatomes charts of the body Anterior surface posterior surface


Segmental innervations of the skeletal muscles :Segmental innervations of the skeletal muscles - The Skeletal muscles receive segmental innervations. - Most muscles are innervated by 2, 3 or 4 segments of the spinal cord and therefore by the same number of spinal nerves. - It is very difficult (impossible) to know the segmental innervations of all muscles of the body. - however, you must know the segmental innervations of some important muscles.


Slide 35:Dr. Bahgat Biceps brachii tendon reflex C5, 6 Triceps tendon Reflex C6, 7, 8 Brachioradialis tendon Reflex C5, 6, 7 Triceps Biceps Brachioradialis Upper limb reflexes


Slide 36:Dr. Bahgat Biceps Tendon


Slide 37:Dr. Bahgat Biceps Reflex Testing


Slide 38:Dr. Bahgat Biceps Reflex Testing - arm supported


Slide 39:Dr. Bahgat Brachioradialis Tendon


Slide 40:Dr. Bahgat Brachioradialis reflex


Slide 41:Dr. Bahgat Triceps Tendon


Slide 42:Dr. Bahgat Triceps Reflex - arm supported


Slide 43:Dr. Bahgat Triceps Reflex, arm unsupported


Important Segmental Innervations of Some muscles :Important Segmental Innervations of Some muscles 1- Biceps brachii tendon reflex: (C5, 6) Flexion of the elbow by taping the biceps tendon. 2- Brachioradialis tendon reflex: (C5,6,7) Flexion of the elbow by taping the brachioradialis tendon. 3- Triceps tendon reflex: (C6, 7, 8) Extension of the elbow by taping the triceps tendon.


Slide 45:Dr. Bahgat Upper abdominal Reflex Middle abdominal Reflex Lower abdominal Reflex Superficial abdominal reflexes T 7 T 8 T 9 T10 T 11 T 12


Slide 46:Dr. Bahgat Segmental innervation of the anterior abdominal wall T 7 T 9 T 11 T 8 T10 T 12 L 1 Supply the umbilicus


Slide 47:4- Abdominal superficial reflexes: Contraction of the abdominal muscles by stroking the overlying skin: - Upper abdominal skin: T 7, 8. - Middle abdominal skin: T 9, 10. - Lower abdominal skin: T 11, 12.


Slide 48:Dr. Bahgat Patellar tendon Reflex L2, 3, 4 Achilles tendon Reflex S1, 2 Lower limb reflexes Quadriceps muscle Tendocalcaneus


Slide 49:5- Patellar tendon reflex: L2 ,3, 4. Extension of the knee joint on taping the patellar tendon. 6- Achilles tendon reflex: S1, 2. Planter-flexion of the ankle joint on taping the Achilles tendon (tendocalcaneus).


Slide 50:References Last’s anatomy Regional and applied (R.M.H. McMinn) – 9th edition Clinical anatomy (Richard S. Snell) – 7th edition Grey’s anatomy – 39th edition


Slide 51:Thank you