Chapter 16 Spinal Cord and Spinal Nerves

Fig (a) Posterior view Cauda equina Sacral part Lumbar part Thoracic part T 1 vertebra Cervical part Atlas Co1 S5 S4 S3 S2 S1 L5 L4 L3 L2 L1 T12 T11 T10 T9 T8 T7 T6 T5 T4 T3 T2 T1 C8 C7 C6 C5 C4 C3 C2 C1 about 42 to 45 cm in adult from base of brain to L 1 vertebra Spinal cord Filum terminale

True spinal cord has cervical part, thoracic part, lumbar part, and sacral part don’t match with vertebrae named for areas served by nerves that exit at that point Spinal cord Fig (a) Posterior view Cauda equina Sacral part Lumbar part Thoracic part T 1 vertebra Cervical part Atlas Co1 S5 S4 S3 S2 S1 L5 L4 L3 L2 L1 T12 T11 T10 T9 T8 T7 T6 T5 T4 T3 T2 T1 C8 C7 C6 C5 C4 C3 C2 C1 Filum terminale

Spinal nerves numbered based on vertebra C2 exits between C 1 and C 2 vertebrae C8 exits between C 7 and T 1 below C8, named for vertebra above exit spot (T6 nerve exits below T 6 vertebra) Nerve numbering Fig (a) Posterior view Cauda equina Sacral part Lumbar part Thoracic part T 1 vertebra Cervical part Atlas Co1 S5 S4 S3 S2 S1 L5 L4 L3 L2 L1 T12 T11 T10 T9 T8 T7 T6 T5 T4 T3 T2 T1 C8 C7 C6 C5 C4 C3 C2 C1 Filum terminale

Fig (c) Conus medullaris and cauda equina Posterior root ganglion Conus medullaris Spinal cord Cauda equina Filum terminale conus medullaris is end of true spinal cord filum terminale is within cauda equina thin strand of pia mater that anchors conus medullaris to coccyx Spinal cord

Posterior median sulcus Anterior median fissure Anterior and posterior sides have divisions posterior median sulcus anterior median fissure Spinal cord

Table 16.1b Gray matter subdivided into horns posterior horns hold axons of sensory neurons and cell bodies of interneurons lateral horns occur only in T1-L2 parts of spinal cord; contain cell bodies of autonomic motor neurons anterior horns hold cell bodies of somatic motor neurons Spinal cord Posterior Anterior Anterior horn Lateral horn Posterior horn Gray commissure Central canal

Table 16.1b Gray commissure provides communication between right and left gray matter Central canal is link to ventricles of brain Spinal cord Posterior Anterior Gray commissure Central canal

Table 16.1d Sacral Cervical Thoracic Lumbar (a) Posterior view Sacral part Lumbar part Thoracic part T 1 vertebra Cervical part Atlas S5 S4 S3 S2 S1 L5 L4 L3 L2 L1 T12 T11 T10 T9 T8 T7 T6 T5 T4 T3 T2 T1 C8 C7 C6 C5 C4 C3 C2 C1

Fig White Matter White matter Posterior funiculus Lateral funiculus White commissure Anterior funiculus Posterior Funiculus is a partition of white matter contains both afferent and efferent neurons Anterior funiculi are joined by white commissure Divisions within funiculi are tracts tracts conduct either sensory or motor impulses

Fig Posterior Spinous process of vertebra Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord Spinal nerve Intervertebral foramen Same meningeal layers as brain layers are continuous with meninges of brain epidural space site between periosteum of vertebra and dura mater site for giving epidural shot Meninges

Fig Posterior Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord epidural space site between periosteum of vertebra and dura mater site for giving epidural shot Meninges

Fig Posterior Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord Meninges dura mater is one layer in spinal cord (2 layers in brain) provides protection for spinal cord at vertebral foramen, extends between vertebrae and fuses with connective tissue surrounding spinal nerve

Fig Posterior Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord Meninges subarachnoid space is filled with CSF site of lumbar puncture

Fig Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Anterior median fissure Central canal Posterior median sulcus White matter Gray matter Spinal Meninges

Fig Posterior rootlets Posterior root Posterior root ganglion Spinal nerve Anterior root Anterior rootlets anterior rootlets extend from spinal cord and merge into anterior root contains motor axons from anterior and lateral horns of spinal cord posterior rootlets merge into posterior root contains sensory axons only has ganglion Nerve structure

17 Intervertebral foramen Spinal nerve Posterior anterior root and posterior root merge into spinal nerve merge within intervertebral foramen Posterior root Anterior root

SAME DAVE Sensory Afferent Motor Efferent Dorsal Arrive Ventral Exit Nerve structure Motor nuclei Sensory nuclei Somatic Autonomic Somatic Visceral

Nerve structure Fig Anterior horn (somatic motor neurons) Anterior root (motor) Spinal nerve (sensory and motor) Somatic motor neuron Autonomic motor neuron Visceral sensory neuron Somatic sensory neuron Posterior root ganglion Posterior root (sensory) Posterior horn (interneurons and sensory axons) Lateral horn (autonomic motor neurons) Components within a typical spinal nerve

Fig Posterior Deep muscles of back Posterior root Posterior root ganglion Posterior ramus Anterior ramus Anterior root Spinal nerve Rami communicantes Sympathetic trunk ganglion Spinal cord Posterior After passing through intervertebral foramen, nerves split into rami posterior ramus is smaller; innervates deep muscles and skin of back anterior ramus is larger; splits into multiple branches innervates anterior and lateral portion of trunk, upper limbs, lower limbs

Rami carry motor and sensory information Signals split lateral to dorsal root ganglion

Fig Posterior Spinal nerve Rami communicantes Sympathetic trunk ganglion Spinal cord Posterior Rami communicantes are axons associated with autonomic nervous system each extends from spinal nerve to sympathetic trunk ganglion ganglia from different nerves interconnected = sympathetic trunk

Fig Sympathetic trunk ganglion Rami communicantes Posterior root ganglion Anterior root Posterior root Anterior ramus Spinal nerve Posterior ramus Sympathetic trunk Intercostal nerves are anterior rami of T1-T11 travel in intercostal space of ribs do not form plexuses (except T1) innervate intercostal muscles receive sensations from anterior and lateral chest wall T7-T12 innervate inferior intercostal spaces and abdominal muscles and skin

Fig C5 C6 Trigeminal nerve (CN V) C2 C3 C4 C5 C2 C3 C4 T2 T1 C5 C6 C7C8 L1 L2 T1 T3 T2 T5 T4 T7 T6 T8 T9 T10 T11 T12 S2 S3 L1 L2 C8C7 C6 C5 T1 T2 L3 L4 L5 S1 Anterior viewPosterior view L5 S1 L4 S1 L3 L5 S1 S2 L2 S2 L1 S1 L5 Co S5 S4 S3 L4 L3 L2 L1 C6 C7 C8 C6 C7 T12 T11 T10 T9 T8 T7 T6 T5 T4 T3 C5 T2 T1 C8 C7 specific segment of skin supplied by a single spinal nerve help to isolate site of spinal injury involved in referred visceral pain = pain from organ felt on skin Dermatomes

Page 492 T7 T6 T5 T4 T3 T2 T1 © Dr. Valerie Dean O’Loughlin Typical dermatomal spread of a shingles rash in a 49-year-old man. Shingles is a reinfection of chicken pox virus (Varicella zoster) that had invaded the posterior root ganglia in the spinal cord if reactivated, travels through sensory axons to dermatomes associated with infected ganglia

Fig Posterior Deep muscles of back Posterior root Posterior root ganglion Posterior ramus Anterior ramus Anterior root Posterior Anterior rami may split and interweave with rami from other nerves, forming a nerve plexus Plexuses innervate body structures (limbs, neck, etc.) Each body structure innervated by rami from several nerves damage to one nerve or one area of spine may not cause complete loss of sensation or movement

Fig Other nerves (not part of cervical plexus) Atlas Axis Hypoglossal nerve (XII) Accessory nerve (XI) Segmental branches Lesser occipital nerve Great auricular nerve Transverse cervical nerve Inferior root Phrenic nerve Supraclavicular nerves Branch to brachial plexus Superior root C4 C3 C1 C2 C5 Anterior rami Cervical plexus branches C4C4 C3C3 C1-C5 nerves; Innervates muscles and skin of neck Cervical plexus Ansa cervicalis

Fig Atlas Axis Hypoglossal nerve (XII) Accessory nerve (XI) Segmental branches Lesser occipital nerve Great auricular nerve Transverse cervical nerve Ansa cervicalis Inferior root Phrenic nerve Supraclavicular nerves Branch to brachial plexus Superior root C4 C3 C1 C2 C5 C4C4 C3C3 Phrenic nerve innervates diaphragm

Brachial plexus Innervates muscles and skin of upper limb, including pectoral girdle

Fig (left) Nerve to subclavius Middle trunk Lateral pectoral nerve Subscapular nerves Lateral cord Posterior cord Musculocutaneous nerve Median nerve Axillary nerve Radial nerve (a) Anterior view Long thoracic nerve Inferior trunk Medial pectoral nerve Thoracodorsal nerve Medial cord Ulnar nerve C5 T1 C7 C8 C6 Brachial plexus Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions Cords: posterior, lateral, medial Terminal branches Superior trunk

Fig (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions Cords: posterior, lateral, medial Terminal branches Superior trunk Middle trunk (a) Anterior view Inferior trunk C5 T1 C7 C8 C6 Roots (anterior rami) from 5 spinal nerves Long thoracic nerve originates from roots Merge in neck into 3 trunks (superior, middle, inferior) Nerve to subclavius originates from superior trunk Brachial plexus Long thoracic nerve Nerve to subclavius

Fig (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions Cords: posterior, lateral, medial Terminal branches Superior trunk Middle trunk (a) Anterior view Inferior trunk C5 T1 C7 C8 C6 Trunks divide into divisions inferior to clavicle to anterior division innervates anterior compartment muscles (flexors) posterior division innervates posterior compartment muscles (extensors) Brachial plexus Anterior division Posterior division

Fig (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions Cords: posterior, lateral, medial Terminal branches Superior trunk Middle trunk (a) Anterior view Inferior trunk C5 T1 C7 C8 C6 In axilla 2 divisions form 3 cords Lateral cord formed from anterior divisions of upper and middle trunk Posterior divisions of 3 trunks form posterior cord Anterior division of inferior trunk becomes medial cord Brachial plexus Anterior division Posterior division Lateral cord Posterior cord Medial cord

Fig (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions Cords: posterior, lateral, medial Terminal branches (a) Anterior view C5 T1 C7 C8 C6 Cords form 5 terminal branches axillary median musculocutaneous radial ulnar Brachial plexus Musculocutaneous nerve Median nerve Axillary nerve Radial nerve Ulnar nerve

Fig (right) Clavicle Lateral cord Posterior cord Medial cord Axillary nerve Musculocutaneous nerve Radial nerve Humerus Ulnar nerve Median nerve Superficial branch of radial nerve Deep branch of radial nerve Ulna Ulnar nerve Median nerve Radius Recurrent branch of median nerve Digital branch of median nerve Deep branch of ulnar nerve Superficial branch of ulnar nerve Digital branch of ulnar nerve (c) Right upper limb, anterior view Scapula Roots (anterior rami) from 5 spinal nerves merge in neck into 3 trunks (superior, middle, inferior) Divide again inferior to clavicle to form anterior division and posterior division In axilla (armpit) 2 divisions form 3 cords (posterior, medial, lateral) cords form 5 terminal branches (axillary, median, musculocutaneous, radial, ulnar) Brachial plexus

Fig (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions Cords: posterior, lateral, medial Terminal branches Superior trunk Middle trunk (a) Anterior view Inferior trunk C5 T1 C7 C8 C6 Roots (Reach) Trunks (To) Divisions (Drink) Cords (Cold) Branches (Beer) Brachial plexus Anterior division Posterior division

Table 16.3a-1 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Posterior cord Teres minor Axillary nerve Deltoid Posterior Motor: deltoid, teres minor Cutaneous (sensory): superolateral arm Axillary nerve

Copyright © McGraw-Hill Education. Permission required for reproduction or display. Table 16.3a-3 Flexor pollicis longus Pronator quadratus Thenar muscles Lateral two lumbricals Anterior Flexor digitorum profundus (lateral half) Flexor digitorum superficialis Palmaris longus Pronator teres Medial cord Posterior cord Lateral cord Flexor carpi radialis Motor: most of anterior forearm, thumb, lateral lumbricals Cutaneous (sensory): lateral side of palm and fingers, dorsal side of tips of digits 1,2,3 and half of 4 Median nerve

Table 16.3b-1 Lateral cord Coracobrachialis Musculocutaneous nerve Biceps brachii Brachialis Anterior Motor: anterior arm muscles Cutaneous (sensory): lateral forearm Musculocutaneous nerve

Table 16.3b-3 Abductor pollicis longus Extensor carpi radialis Brachioradialis Lateral head of triceps brachii Posterior Lateral cord Posterior cord Medial cord Long head of triceps brachii Medial head of triceps brachii Anconeus Supinator Extensor carpi ulnaris Extensor digiti minimi Extensor digitorum Extensor pollicis longus and brevis Extensor indicis Motor: posterior arm, posterior forearm, brachioradialis Cutaneous (sensory): posterior arm, dorsal aspects of lateral 3 digits Radial nerve

Table 16.3c-1 Dorsal and palmar interossei Adductor pollicis Lateral cord Posterior cord Medial cord Flexor carpi ulnaris Flexor digitorum profundus (medial half) Hypothenar muscles Medial two lumbricals Anterior Motor: anterior forearm, intrinsic hand muscles Cutaneous (sensory): dorsal and palmar aspects of pinkie finger and medial half of digit 4 “Funny bone” nerve Ulnar nerve

Fig Anterior divisions Posterior divisions Anterior rami Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Lumbosacral trunk (a) Anterior view L1 L2 L3 L4 L5 Divided into 2 divisions Posterior division Femoral nerve is most important posterior division nerve innervates muscles of anterior compartment Lumbar plexus

Fig Saphenous nerve (continuation of femoral nerve) Obturator nerve Lateral femoral cutaneous nerve Femoral nerve Genitofemoral nerve Ilioinguinal nerve Iliohypogastric nerve (c) Right lower limb, anterior view b: © The McGraw-Hill Companies, Inc./Photos and Dissections by Christine Eckel Sartorius Vastus medialis Pectineus Psoas major Iliacus Femoral nerve Sartorius Rectus femoris Vastus intermedius Vastus lateralis L4 L3 L2 Anterior Motor: anterior thigh muscles Cutaneous (sensory): anterior and interomedial thigh, medial leg and foot Femoral nerve

Divided into 2 divisions Anterior division Obturator nerve is most important anterior nerve innervates muscles of posterior compartment Lumbar plexus Fig Anterior divisions Posterior divisions Anterior rami Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Lumbosacral trunk (a) Anterior view L1 L2 L3 L4 L5

Table 16.4a-3 Obturator externus Adductor brevis Adductor longus Adductor magnus Gracilis Adductor longus Obturator nerve L2 L4 L3 Anterior Fig Saphenous nerve (continuation of femoral nerve) Obturator nerve Lateral femoral cutaneous nerve Femoral nerve Genitofemoral nerve Ilioinguinal nerve Iliohypogastric nerve (c) Right lower limb, anterior view Motor: medial thigh Cutaneous (sensory): superomedial thigh Obturator nerve

Fig (left) Anterior rami Posterior divisions Anterior divisions Superior gluteal nerve Inferior gluteal nerve Nerve to piriformis Sciatic nerve Common fibular division Tibial division Posterior femoral cutaneous nerve Pudendal nerve (a) Anterior view innervate gluteal region, pelvis, perineum, posterior thigh, rest of leg and foot divided into anterior division and posterior division Sacral plexus

Fig (right) Largest and longest in body Tibial and common fibular nerves wrapped in common sheath split just superior to popliteal fossa innervates posterior leg, sole of foot Sciatic nerve Fig (right) Pudendal nerve Posterior femoral cutaneous nerve Superior gluteal nerve Inferior gluteal nerve Sciatic nerve Common fibular nerve Tibial nerve Lateral sural cutaneous nerve Sural nerve Lateral plantar nerve Medial plantar nerve (b) Right lower limb, posterior view

Reflexes –Rapid, automatic, involuntary reactions of muscles or glands to a stimulus –All have similar properties stimulus required to initiate response rapid response requires that few neurons be involved preprogrammed response is the same way every time involuntary response requires no intent or pre-awareness

Fig Stimulus activates receptor Skin Reflex arc

Fig Nerve impulse travels through sensory neuron to the spinal cord 1. Stimulus activates receptor Skin Reflex arc

Fig Interneuron 2. Nerve impulse travels through sensory neuron to the spinal cord 1. Stimulus activates receptor Skin Reflex arc 3. Nerve impulse is processed in the integration center by interneurons Nerve impulse is relayed to the brain by interneuron collaterals

Fig Interneuron 2. Nerve impulse travels through sensory neuron to the spinal cord 1. Stimulus activates receptor Skin 4. Motor neuron transmits nerve impulse to effector Reflex arc 3. Nerve impulse is processed in the integration center by interneurons Nerve impulse is relayed to the brain by interneuron collaterals

Fig Interneuron 2. Nerve impulse travels through sensory neuron to the spinal cord 1. Stimulus activates receptor Skin 4. Motor neuron transmits nerve impulse to effector 5. Effector responds to impulse from motor neuron Reflex arc 3. Nerve impulse is processed in the integration center by interneurons Nerve impulse is relayed to the brain by interneuron collaterals

Monosynaptic Reflex Motor neuron Effector organ Monosynaptic reflex is simplest Sensory neuron synapses directly with motor neuron –ex. knee-jerk reflex Direct communication between sensory and motor neuron (e.g., stretch reflex) Spinal cord Sensory neuron Sensory (stretch) receptor

Fig Sensory nerve endings Intrafusal muscle fiber  motor nerve endings to extrafusal muscle fibers  motor nerve endings to muscle spindle Muscle spindle Knee-jerk response is a stretch reflex Spindles in skeletal muscles monitor stretch Response to stretch is to contract muscle When patellar ligament is struck, quadriceps femoris lengthens quickly, causing reflexive contraction; foot kicks out Stretch reflex

Polysynaptic Reflex Effector organ Motor neuron Interneuron Sensory receptor Interneuron facilitates sensory-motor communication (e.g., withdrawal reflex) Polysynaptic reflexes include more neurons, more complex path –ex. pulling back from hot stove –ex. crossed-extensor reflex: supports postural muscles when you pull your foot back after stepping on a pin Spinal cord Sensory neuron

Reflexes –Can be used to test specific muscle groups, spinal nerves, or sections of spinal cord –hypoactive reflex may indicate damage to spinal cord, muscle disease or damage to neuromuscular junction –hyperactive reflex may indicate damage in brain or spinal cord