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21/04/36 Lecture 4,5,6:Spinal Cord Structure & Function Dr. Amjad El-Shanti MD,MPH, PhD Assistant professor of Public Health- Epidemiology 2014-2015 Grouping of Neural Tissue • White matter: Aggregations of myelin axons from many neurons supported by neuroglia. • The lipid of substance myelin have a whitish color that gives white matter its name • Gray matter: contains either nerve cell bodies, and dendrites or bundles of unmyelinated axons , and neuroglia. • The absence of myelin in these areas accounts for their gray color. 1 21/04/36 • Nerve: A bundle of fibers located outside the central nervous system • The dendrites of somatic afferent neurons and axons of somatic efferent neurons of peripheral nervous system are myelinated, so most nerves are white matter. • Ganglia: A group of nerve cell bodies with other group of cell bodies outside the central nervous system. • Ganglia are masses of gray matter since they are made up of a nerve cell bodies • Tract: A bundle of fibers in the central nervous system. • Tracts may run long distances up and down the spinal cord. • Tracts also exit in the brain and connect parts of the brain with each other and with the spinal cord. • Ascending Tracts: Tracts that conduct impulses up the cord and concerned with sensory impulses. • Descending Tracts: Tracts that carry impulses down the cord and carry motor commands. • The major tracts consist of myelinated fibers and are therefore white matter • Nucleus: A mass of nerve cell bodies and dendrites in the central nervous system. • The nucleus forms gray matter. 2 21/04/36 • Horns (Columns) are the chief areas of gray matter in the spinal cord. • Horn describes the (Two- Dimensional appearance) of the organization of gray matter in the spinal cord (cross-section). • Column describes the (Three-Dimensional appearance) of gray matter in the spinal cord (Longitudinal columns). • The gray matter will be described as arranged in horns, because the white matter also arranged incolumns. 3 21/04/36 General Features of Spinal Cord • Shape: Cylindrical structure (slightly flattened anteriorly & posteriorly. • Location: Extends from the foramen magnum of the occipital bone as a continuation of the medulla oblongata (inferior part of the brain stem) to the level of the second lumbar vertebra. • Length: 42- 45 cm (adult spinal cord) • Diameter: about 2.54 cm at midthoracic, but larger in the lower cervical & midlumbar region 4 21/04/36 • Enlargments: There are two conspicuous enlargements. 1. Cervical enlargement: The superior enlargement extends from the C4 to T1 vertebra. (Nerves that supply the upper extremities arise from the cervical enlargement). 2. Lumbar enlargement: The inferior enlargement extends from T9 to T12 vertebra. (Nerves that supply the lower extremities arise from the lumbar enlargement). • Conus medularis: Ending of spinal cord below the lumbar enlargement as a conical portion at the level of intervertebral disc between the first and second lumbar vertebra • Filum terminale: Anon-nervous fibrous tissue of the spinal cord that extends inferiorly to attach to the coccyx. (consists mostly of pia matter: inner most of three membranes that cover and protect the spinal cord and brain) • Cauda equina: (Horse’s tail) Some nerves that arise from lower portion of the cord do not leave the vertebral column immediately but angle inferiorly in the vertebral canal like wips of coarse hair flowing from the end of the cord. • Spinal segment: A region of spinal cord from which a pair of spinal nerves arises. • Spinal cord is a series of 31 segments, each giving rise to a pair of spinal nerves. • Anterior median fissure: Deep wide groove on the anterior (ventral) surface of spinal cord. • Posterior median sulcus: shallower narrow groove on the posterior (dorsal) surface of spinal cord. • The spinal cord is divided into right & left sides by the above two grooves 5 21/04/36 Protection of Spinal Cord The spinal cord is protected by different structures: A. B. C. D. 6 Vertebral column Meninges Ligaments Cerebrospinal fluid (CSF) 21/04/36 A. Vertebral Canal • The spinal cord is located in the vertebral column. • The canal is formed by the vertebral foramina of all vertebrae arranged on top of each other. • The cord is well protected, because the wall of vertebral canal is essentially a ring of bone surrounding the spinal cord. B. Spinal Meninges • Meninges: Are coverings that run continuously around the spinal cord & brain. • There are three layers of membranes that cover the spinal cord arranged from outside to inside respectively as following: 1. Dura matter (Outermost layer). 2. Arachnoid layer (Middle layer). 3. Pia matter (Innermost layer). 7 21/04/36 • • • • • Dura matter The outer spinal meninx. (Tough mother). It forms a tube from the level of S2 vertebra, where it is fused with the filum terminale, to the foramen magnum, where it is continuous with the dura matter of brain. It is composed of dense fibrous connective tissue. Epidural Space: Space between the dura matter and the wall of vertebral canal. Epidural space is filled with: 1. Fat 2. Connective tissue 3. Blood vessels • • Epidural space serves as a padding around the cord. Epidural space inferior to L2 vertebra is the site for the injection of anesthetics. Arachnoid Layer • The middle spinal meninx . (Spider layer). • It is a delicate connective tissue membrane that forms a tube inside the dura matter. • It is continuous with arachnoid of the brain. • Subdural Space: Space between the dura matter and the arachnoid contains serous fluid. 8 21/04/36 • • • • Pia matter The inner meninx. (Delicate mother). It is transparent fibrous membrane that forms a tube around and adheres to the surface of the spinal cord & brain. It contains numerous blood vessels. Subarachnoid space: Space between the arachnoid and the pia matter, where the cerebrospinal fluid (CSF) circulates. • All three spinal Meninges cover the spinal nerves up to the point of exit from the spinal column through the intervertebral foramina. 9 21/04/36 C. Ligaments • Denticulate Ligaments: Are extensions of pia matter attached laterally to the dura matter along the length of the cord between the ventral and dorsal roots of spinal nerves on either side • Denticulate Ligaments protect spinal cord against shock & sudden displacement. • Summary: Spinal cord is fixed in its position in the vertebral canal by: 1. Filum Terminale which anchored to the coccyx inferiorly. 2. Denticulate Ligaments laterally to the dura matter 3. Superiorly to the brain 10 21/04/36 Structure of spinal cord in cross section • The spinal cord consists of both gray and white matter. • Gray matter consists primarily of nerve cell bodies and unmyelinated axons and dendrites of association and motor neurons. • White matter consists of bundles of myelinated axons of motor and sensory neurons. • Gray matter forms H- shaped area within the white matter. • Gray commissure The cross bar of h shaped area. • Central canal small space in the central of gray commissure runs the length of spinal cord with continuation with the fourth ventricle of fourth brain. • Anterior (Ventral) white Commissure Bar connects the white matter of left & right side of spinal cord. 11 21/04/36 1 Spinal Nerve 5 Central Canal 2 Dorsal Root Ganglion 6 Grey Matter 3 Dorsal Root (Sensory) 7 White Matter 4 Ventral Root (Motor) Gray Matter of Spinal Cord • Anterior (Ventral) gray horns: The motor part of gray matter closer to the front of the cord • Posterior (Dorsal) gray horns: The sensory part of gray matter closer to the back of the cord. • Lateral (Intermediate) gray horns: The region between the anterior & posterior gray horns • The gray matter contains several nuclei that serve as relay stations for impulses and origins for certain nerves. • Nuclei: are clusters of nerve cell bodies and dendrites in the spinal cord and brain. 12 21/04/36 White Matter of spinal cord • The white matter like the gray matter is organized into regions divided by anterior & posterior gray horns into 3 broad areas: 1. 2. 3. • • • • • 13 Anterior white Columns Posterior white Columns Lateral white Columns Column (Funiculus) consists of bundles of myelinated fibers run the length of the cord. Tracts (Fasiculi): Bundles of fibers Ascending tracts: Sensory axons that conduct impulses that enter the spinal cord upward to the brain. (Sensory Tracts) Descending Tracts: Motor axons that conduct impulses from the brain downward into the spinal cord which synapse with other neurons whose axons pass out to muscles and glands. (Motor Tracts) Short Tracts: Ascending and Descending axons that convey impulses from one level of the cord to other. 21/04/36 Function of Spinal Cord 1. Convey sensory impulses from the periphery to the brain, and conduct motor impulses from the brain to the periphery. 2. Provide means of integrating reflexes. Spinal Tracts • • • 1. 2. 3. 4. 14 Vital function of spinal tracts is to convey sensory & motor information to & from the brain. These informations are carried by Ascending & descending tracts of spinal cord. Names of Spinal Tracts: indicates the followings: White column (Funiculus) in which the tract travels. Where the cell bodies of the tract originate Where the axons of the tract terminate The direction of impulse conduction E.g. Anterior Spinothalamic Tract Origin : Spinal cord, Termination: Thalamus, Direction : Ascending 21/04/36 Ascending & Descending Tracts Ascending Tracts Location (White Column) Origin Termination Function Anterior Spinothalamic Anterior column Posterior gray horn, crossed to opposite side of brain Thalamus, Impulses eventually conveyed to cerebral cortex Touch , pressure sensations from one side of body to opposite side of thalamus. Eventually reach cerebral cortex. Lateral spinothalamic Lateral column Posterior gray horn, crossed to opposite side brain Thalamus, Impulses eventually conveyed to cerebral cortex Pain, temperature sensations from one side of body to opposite side of thalamus. Eventually reach cerebral cortex. Posterior column Axons of afferent neurons from periphery that enter posterior column on one side of cord and rise to same side of brain Nucleus gracilis & nucleus cuneatus of medulla, impulses conveyed to cerebral cortex eventually 1-Two-point discrimination 2-proprioception 3- stereognosis 4-weight discrimination 5- vibration From one side To same side of medulla . Eventually reach cerebral cortex. Fasciculus gracilis & Fasciculus cuneatus 15 Posterior spinocerebellar Posterior portion of lateral column Posterior gray horn, rises to same side of brain cerebellum Sensations from one side of body to same side of cerebellum for subconscious proprioception. Anterior spinocerebellar Anterior portion of lateral column Posterior gray horn, contains both crossed & uncrossed fibers cerebellum Sensations from both sides of body to cerebellum for subconscious proprioception. 21/04/36 • Two-point discrimination: Ability to distinguish that two points on skin are touched even though close together. • Proprioception: Awareness of precise position of body parts and their direction of movement. • Stereognosis: ability to recognize size, shape and texture of object. • Weight discrimination: Ability to assess weight of an object Lateral Spinothalamic Tract 16 21/04/36 Fasciculus gracilis & Fasciculus Cuneatus Spinocerebellar Tracts 17 21/04/36 Descending Tracts Location (White Column) Origin Termination Function Lateral Corticospinal Lateral column Cerebral cortex on one side of brain but crosses in base of medulla to opposite side of cord Anterior gray horn Motor impulses from one side of cortex to anterior gray horn of opposite side. Eventually reach skeletal muscle on opposite side of body that coordinate precise discrete movements. Anterior Corticospinal Anterior Column Cerebral cortex on one side, uncrosses in medulla, but crosses to opposite side of cord Anterior gray horn Motor impulses from one side of cortex to anterior gray horn of same side. But cross to opposite side in spinal cord and reach skeletal muscles that coordinate discrete movement. Rubrospinal Lateral Column Midbrain (Red nucleus) on one side of brain, but crosses to opposite side of cord. Anterior gray horn Motor impulses from one side of midbrain to skeletal muscles on opposite side of body that are concerned with muscle tone and posture. Tectospinal Anterior Column Midbrain (Red nucleus) on one side of brain, but crosses to opposite side of cord. Anterior gray horn Motor impulses from one side of midbrain to skeletal muscles on opposite side of body that control movements of head in response to auditory, visual, and cutaneous stimulation Vestibulospinal Anterior Column Medulla on one side of brain and descends to same side of cord Anterior gray horn Motor impulses from one side of medulla to skeletal muscles on same side of body that regulate body in tone in response to movements of head (equilibrium). Descending Tracts 18 21/04/36 Reflex Center • The second principal function of spinal cord is to serve as center for reflex action. • Spinal nerves are the paths of communication between the spinal cord tracts and the periphery. • Dorsal Root (sensory): contains sensory nerve fibers only and conducts impulses from the periphery to the spinal cord. Fibers extend into the posterior gray horn • Dorsal Root Ganglion: swelling contains the cell bodies of the sensory neurons from the periphery. • Ventral Root (Motor): contains motor nerve fibers only and conduct impulses from the spinal cord to the periphery. • Cell bodies of the motor neurons are located in the gray matter of the cord. • If motor impulses supplies a skeletal muscle, the cell bodies located in anterior gray horn. • If motor impulses supplies a smooth muscle, cardiac muscle & a gland, the cell bodies located in lateral gray horn. (Autonomic Nervous System). 19 1 Spinal Nerve 5 Central Canal 2 Dorsal Root Ganglion 6 Grey Matter 3 Dorsal Root (Sensory) 7 White Matter 4 Ventral Root (Motor) 21/04/36 • • • Reflex Arc &Homeostasis Conduction pathway : The path an impulse follows from its origin in the dendrites or cell body of a neuron in one part of the body. (Circuits of neurons). Reflex Arc: Functional unit of the nervous system contains two or more neurons over which impulses are conducted from a receptor to the brain or spinal cord and then to the effector. ( one pathway). Function of Reflex Arc: Responding to a change in the internal or external environment. Responding to preserve homeostasis. • Components of Reflex Arc : 1. Receptor: The distal end of a dendrite or a sensory structure with the distal end of a dendrite. 2. Sensory Neuron: Passes the impulse from receptor to its axonal terminal in CNS. 3. Center: A region in the central nervous system where an incoming sensory impulse generates an outgoing motor impulse. 4. Motor Neuron: Transmit the impulse generated by the sensory or association neuron in the center to the organ of body that will respond. 5. Effector : The organ of body (muscle, gland) that responds to the motor impulse. • Responding= Reflex 20 21/04/36 • In the center, the impulse may be inhibited or transmitted or rerouted. • In the center of : some reflex arcs, the sensory neuron directly generates the impulse in the motor neuron. The center may contain association neuron between the sensory neuron and motor neuron. Reflex Arc components 21 21/04/36 Reflexes Features & Types • Reflexes are fast responses to changes in the internal or external environment that allow the body maintain homeostasis. • Reflexes are associated not only with skeletal muscle contraction but also with body functions ( heart rate, respiration, digestion, urination, & deification). • Spinal reflexes: Reflexes carried out by spinal cord alone • Spinal reflexes are either somatic reflexes or Visceral Reflexes. • Somatic reflexes: Reflexes that result in contraction of skeletal muscles. • Visceral (Autonomic ) reflexes: reflexes cause the contraction of smooth or cardiac muscle or secretion by glands. Somatic Spinal Reflexes 1. 2. 3. 4. 22 Stretch Reflex Tendon Reflex Flexor (Withdrawal) Reflex Crossed Extensor Reflex 21/04/36 Characters Stretch Reflex Tendon Reflex Flexor Reflex Crossed Extensor Synapse Monosynaptic (at anterior gray horn) polysynaptic Polysynaptic polysynaptic stimulus Rapid Stretching of muscle (Change in the length of muscle): degree, rate Change in muscle tension caused by passive stretch or muscular contraction Painful (Noxious) stimulus (nail, Tack) Painful (Noxious) stimulus (nail, Tack) Receptor Muscle Spindle Golgi tendon organ Cutaneous (skin) and pain receptors Cutaneous (skin) and pain receptors pathway Ipsilateral Ipsilateral Ipsilateral & intersegmental (Ascending & Descending branches) Contralateral Response Contraction of stretched muscle Relaxation of muscle which its tendon stretched Several motor responses Opposite to action of muscles affected bt flexor reflex Function 1- essential for maintaining of muscle tone 2-Important for muscle function during exercise 3- prevent injury from over stretching Protection of tendon & their muscles from damage that might be brought by excessive tension (Protective reflex) Withdrawing of affected extremity to avoid pain Cross extension aids in maintaining posture when leg is lifted Reciprocal innervation Yes: inhibition of antagonistic muscles Yes: excitation of antagonistic muscles Yes: Inhibition of antagonistic muscles Yes: excitation of antagonistic muscles e.g. Patellar reflex (Tapping Quadriceps femoris muscle) Large force on tendon (pull on muscle when resisted) Sharp, painful stimulus (as in stepping on nail) Sharp, painful stimulus (as in stepping on nail) • • • • • • • • 23 Monosynaptic reflex Arc: There is only one synapse in the pathway (only two neurons are involved). Polysynaptic reflex arc: More than two neurons are involved, there is more than one synapse. Ipsilateral reflex: The sensory impulse enters the spinal cord on the same side that the motor impulse leaves the spinal cord. Contralateral reflex: The sensory impulse enters one side of the spinal cord & exits on the opposite side. Reciprocal Innervation: Phenomenon by which impulses stimulate contraction of muscle and simultaneously inhibit contraction of antagonistic muscles. Reciprocal innervation is important to avoid conflict between prime movers and antagonists, an is vital in coordinating body movements. Inhibition of antagonistic muscles: inhibition of contraction of antagonistic muscles (Extension of antagonistic muscles). Excitation of antagonistic muscles: excitation of contraction of antagonistic muscles (flexion of antagonistic muscles). 21/04/36 Stretch & tendon Reflexes Flexor & Crossed Extensor Reflexes 24 21/04/36 Reflexes and Diagnosis • • • • • Reflexes are often used for diagnosis disorders of the nervous system and locating the injured tissue. If a reflex cease to function or if functions abnormally, the specialist may suspect that the damage lies somewhere along a particular conduction pathway. Visceral reflexes are usually not practical tools for diagnosis, since they are deep in the body. Somatic reflexes can be tested simply by tapping or stroking the body. The reflexes of clinical significance are: 1. Patellar reflex. 2. Achilles reflex. 3. Babinski sign. 4. Abdominal reflex. Spinal Nerves 25 21/04/36 Names of Spinal Nerves • • • • The 31 pairs of spinal nerves are named & numbered according to the region and level of spinal cord from which they emerge. The first cervical pair emerges between the atlas & the occipital bone. All other spinal nerves leave the vertebral column from the intervertebral foramina between adjoining vertebrae. There are: 1. 2. 3. 4. 5. 8 pairs of cervical nerves 12 pairs of thoracic nerves 5pairs of lumbar nerves 5 pairs of sacral nerves 1 pair of coccygeal nerves Composition & Coverings of Spinal Nerves • A spinal nerve has two points of attachments (posterior root &anterior root). • The posterior &anterior roots unite to form a spinal nerve at the intervertebral foramen. • The spinal nerve is a mixed nerve since the posterior root contains sensory fibers, and the anterior root contains motor fibers. • The individual fibers, whether myelinated or unmyelinated are wrapped in a connective tissue called the Endoneurium. • Groups of fibers with their endoneurium in bundles called Fascicles. • Each fascicle is wrapped in connective tissue called Perineurium. • The outermost covering around entire nerve is the Epineurium. • The spinal meninges fuse with the epineurium as the nerve exits from the vertebral canal. 26 21/04/36 Coverings of spinal nerves Distribution of Spinal nerves 27 21/04/36 Branches of spinal nerve • After a spinal nerve leaves its intervertebral foramen, it divides into several branches (Rami): 1. Dorsal ramus: innervates the deep muscles and skin of dorsal surface of the back. 2. Ventral ramus: innervates the superficial back muscles and all the structures of the extremities and the lateral and ventral trunk. 3. Meningeal branch: reenters the spinal canal through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord and the meninges. 4. Rami communicants: components of autonomic nervous system. Cross-Section of Spinal Cord 28 21/04/36 Plexuses • • Plexus: Networks of ventral rami of spinal nerves with adjacent nerves on either side of the body (except for thoracic nerves T2-T11). The principal plexus are: 1. 2. 3. 4. • • Cervical plexus Brachial plexus Lumbar plexus Sacral plexus Emerging from the plexuses are nerves bearing names that are often descriptive of the general regions that supply. Each nerve have several branches named for the specific structures they innervate. plexuses 29 21/04/36 Cervical plexus • Deep in the side of the neck, just even with the initial 4 cervical vertebrate, there lies the cervical plexus. • The anterior rami of the initial 4 cervical nerves with combination of C5 designate the nerve fibers which create this particular plexus • The cervical plexus creates numerous branches and then innervate the various related structures, such as the skin and muscles of the neck and the appropriate surrounding skin and muscles of the shoulders and head. • A few muscles belonging to the neck and pharynx receive a few extra nerve fibers, derived from the cervical plexus and a combination of the accessory and hypoglossal cranial nerves that all mesh into one in order to serve this area. • The phrenic nerve is created by the unification of the third, fourth, and fifth cervical nerve. • The phrenic nerve is responsible for innervating the diaphragm. • The diaphragm contracts, which expels air into the lungs, due to the commands of the motor impulses relayed by the phrenic nerve. Branches of • The cervical plexus has two types of branches: cutaneous and muscular. A. Cutaneous (4 branches): A. Lesser occipital nerve - innervates lateral part of occipital region (C2,C3) B. Greater auricular nerve - innervates skin near concha auricle and external acoustic meatus (C2&C3) C. Transverse cervical nerve - innervates anterior region of neck (C2&C3) D. Supraclavicular nerves - innervate region of suprascapularis, shoulder, and upper thoracic region (C3,C4) B. Muscular A. Ansa cervicalis (loop formed from C1-C3), etc. (geniohyoid (C1 only), thyrohyoid (C1 only), sternothyroid, sternohyoid, omohyoid) B. Phrenic Nerve (C3-C5) :Diaphragm 30 21/04/36 Brachial plexus • The brachial plexus is an arrangement of nerve fibres, running from the spine, specifically from above the fifth cervical vertebra to underneath the first thoracic vertebra (C5-T1). • It proceeds through the neck, the axilla (armpit region) and into the arm. • The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle innervated by the spinal accessory nerve and an area of skin near the axilla innervated by the intercostobrachialis nerve. • This function may be impaired by tumor growth of the Apical region of either Lung. • Therefore, brachial plexus lesions can lead to severe functional impairment. 31 21/04/36 Path of Brachial Plexus • • • One can remember the order of brachial plexus elements by way of the mnemonic, "Read The Damn Cadaver Book" (Or, alternatively, Randy Travis Drinks Cold Beer") - Roots, Trunks, Divisions, Cords, Branches or Roots, Trunks, Divisions, Cords, Collateral/Pre-terminal Branches, and (Terminal) Branches. The five roots are the five anterior rami of the spinal nerves, after they have given off their segmental supply to the muscles of the neck. These roots merge to form three trunks: – "superior"or "upper" (C5-C6) – "middle" (C7) – "inferior"or "lower" (C8-T1) • Each trunk then splits in two, to form six divisions: – anterior division of the superior, middle and inferior trunks – posterior division of the superior, middle, and inferior trunks • These six divisions will regroup to become the three cords. The cords are named by their position in respect to the axillary artery. – The posterior cord is formed from the three posterior divisions of the trunks (C5T1) – The lateral cord is the anterior divisions from the upper and middle trunks (C5C7) – The medial cord is simply a continuation of the lower trunk (C8-T1) • The branches are listed below. Most branch from the cords, but a few branch directly from earlier structures. • Three important nerves arising from brachial plexus: 1. Radial nerve: supplies the muscles on the posterior aspect of the arm and the forearm. (Posterior cord: C5-T1) 2. Median nerve: supplies most of the muscles of the anterior forearm and some of the muscles in the palm. (union of Lateral & Medial cords: C5-T1) 3. Ulnar nerve: supplies the anteromedial muscles of the forearm an most of the muscles of the palm. (Medial cord: C8-T1) 32 21/04/36 Nerves & Distributions of Brachial Plexus From Nerve Roots Muscles Cutaneous roots dorsal scapular nerve C5 rhomboid muscles and levator scapulae - roots long thoracic nerve C5, C6, C 7 serratus anterior - superior trunk nerve to the subclavius C5, C6 subclavius muscle - superior trunk suprascapular nerve C5, C6 supraspinatus and infraspinatus - lateral cord lateral pectoral nerve C5, C6, C 7 pectoralis major (by communicating with the medial pectoral nerve) - lateral cord musculocutaneous nerve C5, C6, C 7 coracobrachialis, brachialis and biceps brachii becomes the lateral cutaneous nerve of the forearm lateral cord lateral root of the median nerve C5, C6, C 7 fibres to the median nerve - posterior cord upper subscapular nerve C5, C6 subscapularis (upper part) - posterior cord thoracodorsal nerve (middle subscapular nerve) C6, C7, C 8 latissimus dorsi - posterior cord lower subscapular nerve C5, C6 subscapularis (lower part ) and teres major - posterior cord axillary nerve C5, C6 anterior branch: deltoid and a small area of overlying skin posterior branch: teres minor and deltoid posterior branch becomes upper lateral cutaneous nerve of the arm muscles 33 posterio r cord radial nerve C5, C6, C7, C8, T1 triceps brachii, supinator, anconeus, the extensor muscles of the forearm, and brachioradialis skin of the posterior arm as the posterior cutaneous nerve of the arm medial cord medial pectoral nerve C8, T1 pectoralis major and pectoralis minor - medial cord medial root of the median nerve C8, T1 fibres to the median nerve portions of hand not served by ulnar or radial medial cord medial cutaneous nerve of the arm C8, T1 - front and medial skin of the arm medial cord medial cutaneous nerve of the forearm C8, T1 - medial skin of the forearm medial cord ulnar nerve C8, T1 flexor carpi ulnaris, the medial 2 bellies of flexor digitorum profundus, most of the small muscles of the hand the skin of the medial side of the hand and medial one and a half fingers on the palmar side and medial two and a half fingers on the dorsal side 21/04/36 Brachial Plexus Lumbar Plexus • The lumbar plexus is a nervous plexus in the lumbar region of the body. • It is formed by the loops of communication between the anterior divisions of the first three and the greater part of the fourth lumbar nerves; the first lumbar often receives a branch from the last thoracic nerve. • It is situated in the posterior part of the Psoas major, in front of the transverse processes of the lumbar vertebræ 34 21/04/36 Branches of Lumbar plexus • The lumbar plexus differs from the brachial plexus in not forming an intricate interlacement, but the several nerves of distribution arise from one or more of the spinal nerves, in the following manner: • The first lumbar nerve, frequently supplemented by a twig from the last thoracic, splits into an upper and lower branch; the upper and larger branch divides into the iliohypogastric and ilioinguinal nerves; the lower and smaller branch unites with a branch of the second lumbar to form the genitofemoral nerve. • The remainder of the second lumbar nerve, and the third and fourth lumbar nerves, divide into ventral and dorsal divisions. • The ventral division of the second lumbar nerve unites with the ventral divisions of the third and fourth lumbar nerves to form the obturator nerve. • The dorsal divisions of the second and third nerves divide into two branches, a smaller branch from each uniting to form the lateral femoral cutaneous nerve, and a larger branch from each joining with the dorsal division of the fourth nerve to form the femoral nerve (The largest nerve arising from the lumbar plexus). • The accessory obturator, when it exists, is formed by the union of two small branches given off from the third and fourth nerves. Nerves & Distributions of Lumbar plexus 35 Division Name Source Target Main Iliohypogastric nerve 1 L. Skin over the lateral gluteal region and above the pubis Main Ilioinguinal nerve 1 L. Skin over the root of the penis and upper part of the scrotum (male), skin covering the mons pubis and labium majus (female) Main Genitofemoral nerve 1, 2 L. Genital Branch: Cremaster muscle, skin of scrotum/labia majora Femoral Branch: Skin on anterior thigh Dorsal Lateral femoral cutaneous 2, 3 L. Skin on the lateral part of the thigh Ventral Obturator nerve (and Accessory obturator nerve, when present) 2, 3, 4 L. Medial compartment of thigh Dorsal Femoral nerve 2, 3, 4 L. Anterior compartment of thigh Ventral Lumbosacral trunk 4, 5L., 1, 2, 3, 4 S. Sacral plexus [1] 21/04/36 Lumbar Plexus Sacral Plexus • In human anatomy, the sacral plexus is a nerve plexus emerging from the sacral vertebrae (S1-S4), and which provides nerves for the pelvis and lower limbs. • The sacral plexus lies on the back of the pelvis between the piriformis muscle and the pelvic fascia. • In front of it are the internal iliac artery, internal iliac vein, the ureter, and the sigmoid colon. • The superior gluteal artery and vein run between the lumbosacral trunk and the first sacral nerve, and the inferior gluteal artery and vein between the second and third sacral nerves. 36 21/04/36 Branches of Sacral plexus • 1. 2. 3. • • • • • The sacral plexus is formed by: the lumbosacral trunk the anterior division of the first sacral nerve portions of the anterior divisions of the second, third and fourth sacral nerves The nerves forming the sacral plexus converge toward the lower part of the greater sciatic foramen, and unite to form a flattened band, from the anterior and posterior surfaces of which several branches arise. The band itself is continued as the sciatic nerve, which splits on the back of the thigh into the tibial nerve and common fibular nerve; these two nerves sometimes arise separately from the plexus, and in all cases their independence can be shown by dissection. The largest nerve in the body is the sciatic nerve. The Sciatic nerve supplies the entire musculature of leg and foot. Often, the sacral plexus and the lumbar plexus are considered to be one large nerve plexus, the lumbosacral plexus. The lumbosacral trunk connects the two plexuses. Nerves & Distributions of Sacral Plexus 37 Nerve Segmen ts Muscles Nerve to quadratus femoris L4-S1 gemellus inferior, quadratus femoris Superior gluteal nerve L4-S1 gluteus medius, gluteus minimus, tensor fasciae latae Sciatic nerve L4-S3 * Tibial nerve L4-S3 posterior compartment posterolateral leg and foot - medial sural cutaneous nerve * Common fibular (Peroneal) nerve L4-S3 anterior compartment and lateral compartment anterolateral leg and foot - Lateral sural cutaneous nerve, medial dorsal cutaneous nerve, intermediate dorsal cutaneous nerve Nerve to obturator internus L5-S2 gemellus superior, obturator internus Inferior gluteal nerve L5-S2 gluteus maximus Nerve to piriformis S1-S2 piriformis Cutaneous 21/04/36 Posterior cutaneous nerve of thigh S1-S3 - Thigh & Buttock Perforating cutaneous nerve S2-S3 - Buttock Pudendal nerve S2-S4 bulbospongiosus, deep transverse perineal, ischiocavernosus, sphincter urethrae, superficial transverse perineal clitoris, penis Coccygeal nerve S4-Co1 - perineu m Sacral Plexus 38 21/04/36 Thoracic (Intercostal ) Nerves • Spinal nerves T2-T11 do not enter into the formation of plexuses. • Nerves T2-T11 are known as Intercostal (Thoracic) nerves. • They are distributed directly to the structures they supply in the intercostal spaces. • After leaving its intervertebral foramen, the ventral ramus of nerve T2 supplies the intercostal muscles of the skin and the skin of the axilla and posteromedial aspect of the arm. • Nerves T3-T6 pass in the costal grooves of the ribs and are distributed to the intercostal muscles and skin of the anterior and lateral chest wall. • Nerves T7-T11 supply the intercostal muscles and the abdominal muscles and overlying skin. • The dorsal rami of the intercostal nerves supply the deep back muscles and skin of the dorsal aspect of the thorax. Dermatomes • Dermatome is a Greek word which literally means "skin cutting". • A dermatome: is an area of the skin supplied by nerve fibers originating from a single dorsal nerve root. • The dermatomes are named according to the spinal nerve which supplies them. • The dermatomes form into bands around the trunk but in the limbs their organisation is more complex as a result of the dermatomes being "pulled out" as the limb buds form and develop into the limbs during embryological development. 39 21/04/36 • In diagrams or maps, the boundaries of dermatomes are usually sharply defined. • However, in life there is considerable overlap of innervation between adjacent dermatomes. Thus, if there is a loss of afferent nerve function by one spinal nerve sensation from the region of skin which it supplies is not usually completely lost as overlap from adjacent spinal nerves occurs: however, there will be a reduction in sensitivity. Dermatome Map of the Body 40 21/04/36 Spinal cord injury • 1. 2. 3. 4. 5. 6. 7. Causes: Tumors Blood Clots Degenerative disorders Demylination disorders Fracture of the vertebrae Dislocation of the vertebrae Penetrating wounds by projectile metal fragments. 8. Traumatic events (Automobile Accidents). Plegia: Paralysis • The paralysis which caused due to spinal cord injury depends on the location and extent of the injury: • Monoplegia: paralysis of one extremity only. • Diplegia: paralysis of both upper extremities or both lower extremities. • Paraplegia: paralysis of both lower extremities. • Hemiplegia: paralysis of the upper extremity, trunk, and lower extremity of one side of the body. • Quadriplegia: paralysis of the two upper and two lower extremities. 41 21/04/36 • Complete Transection of the spinal cord: The cord is cut transversely and severed from one side to the other side. The following results: 1. 2. Loss of all sensations below the level of transection Loss of all voluntary movement blow the level of transection A. B. • If the upper cervical cord is transected: quadriplegia results. If the Transection is between the cervical & lumbar enlargements: paraplegia results. Partial Transection (Hemisection): below the hemisection, the following results: 1. 2. 3. A. B. Loss of proprioception, tactile discrimination, and feeling of vibration on the same side of injury. Paralysis on the same side. Loss of feelings of pain and temperature on the opposite side. If the hemisection is of the upper cervical cord , Hemiplegia results. If the hemisection of the thoracic cord , paralysis of one lower extremity results (Monoplegia). • Spinal Shock: An initial period following transection lasts from a few days to several weeks characterized by areflexia condition. • During this period, all reflex activity is abolished (Areflexia). • After this period, there is return of reflex activity. • The first reflex to return is the knee jerk. Its appearance may take several days. • Next, the flexion reflexes return over a period of up to several months. • Then the crossed extensor reflexes return. 42 21/04/36 Delayed Nerve Grafting • • • • Severe damage resulting from transection was thought to be irreversible. Technique for regenerating severed spinal cords in animals is developed recently. This technique is called Delayed Nerve Grafting . Delayed Nerve Grafting: 1. Cutting the crushed or injured section of the spinal cord 2. Bridging the gap with nerve segments from the arm or the leg. 3. The original served axons in the cord can grow through the bridge. 43