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Chapter 16 Spinal Cord and Spinal Nerves Fig. 16.1 C1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 L4 L5 S1 S2 S3 S4 S5 Atlas Spinal cord Cervical part • about 42 to 45 cm in adult • from base of brain to L1 vertebra T1 vertebra Thoracic part Lumbar part Sacral part Cauda equina Filum terminale Co1 (a) Posterior view Fig. 16.1 C1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 L4 L5 S1 S2 S3 S4 S5 Co1 Atlas Cervical part Spinal cord T1 vertebra Thoracic part Lumbar part Sacral part Cauda equina Filum terminale (a) Posterior view • 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 Fig. 16.1 C1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 L4 L5 S1 S2 S3 S4 S5 Co1 Atlas Cervical part T1 vertebra Thoracic part Lumbar part Sacral part Cauda equina Filum terminale (a) Posterior view Nerve numbering • Spinal nerves numbered based on vertebra • C2 exits between C1 and C2 vertebrae • C8 exits between C7 and T1 • below C8, named for vertebra above exit spot (T6 nerve exits below T6 vertebra) Fig. 16.1 Spinal cord • conus medullaris is end of true spinal cord • filum terminale is within cauda equina Spinal cord Conus medullaris • thin strand of pia mater that anchors conus medullaris to coccyx Cauda equina Posterior root ganglion Filum terminale (c) Conus medullaris and cauda equina Spinal cord • Anterior and posterior sides have divisions • posterior median sulcus • anterior median fissure Posterior Posterior median sulcus Anterior median fissure Table 16.1b Posterior Spinal cord • Gray matter subdivided into horns Posterior horn • posterior horns hold Lateral horn axons of sensory neurons and cell bodies Anterior horn of interneurons • lateral horns occur only Anterior in T1-L2 parts of spinal cord; contain cell bodies Central canal of autonomic motor Gray commissure neurons • anterior horns hold cell bodies of somatic motor neurons Table 16.1b Spinal cord Posterior Central canal • Gray commissure provides communication between right and left gray matter • Central canal is link to Gray commissure ventricles of brain Anterior Table 16.1d C1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 L4 Atlas Cervical part T1 vertebra Cervical Thoracic part Thoracic Lumbar part Sacral part L5 S1 S2 S3 S4 S5 (a) Posterior view Lumbar Sacral Fig. 16.3 White Matter • Funiculus is a partition of white matter White matter Posterior funiculus Lateral funiculus White commissure Anterior funiculus • 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 Posterior Fig. 16.2 Meninges Posterior Spinous process of vertebra Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal nerve Intervertebral foramen Spinal cord • 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 Fig. 16.2 Meninges Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord Posterior • epidural space site between periosteum of vertebra and dura mater • site for giving epidural shot Fig. 16.2 Meninges Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord Posterior • 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. 16.2 Meninges Posterior Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord • subarachnoid space is filled with CSF • site of lumbar puncture Fig. 16.2 Spinal Meninges White matter Gray matter Posterior median sulcus Central canal Anterior median fissure Pia mater Subarachnoid space Arachnoid mater Subdural space Dura mater Fig. 16.2 Nerve structure 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 Posterior • anterior root and posterior root merge into spinal nerve • merge within intervertebral foramen Posterior root Spinal nerve Anterior root Intervertebral foramen 17 Nerve structure • SAME DAVE • Sensory Afferent Motor Efferent • Dorsal Arrive Ventral Exit Somatic Visceral Autonomic Somatic Sensory nuclei Motor nuclei Nerve structure Fig. 16.4 Components within a typical spinal nerve Posterior root (sensory) Posterior horn (interneurons and sensory axons) Posterior root ganglion Somatic sensory neuron Visceral sensory neuron Autonomic motor neuron Somatic motor neuron Spinal nerve (sensory and motor) Lateral horn (autonomic motor neurons) Anterior root (motor) Anterior horn (somatic motor neurons) Posterior Posterior Fig. 16.5 Deep muscles of back Posterior root Posterior root ganglion Posterior ramus Spinal cord Anterior ramus Spinal nerve Anterior root • After passing through intervertebral foramen, nerves split into rami Rami communicantes Sympathetic trunk ganglion • 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 Posterior Posterior Fig. 16.5 • 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 Spinal cord Spinal nerve Rami communicantes Sympathetic trunk ganglion Fig. 16.7 Spinal nerve Posterior ramus Posterior root Anterior root Anterior ram Posterior root ganglion Rami communicantes Sympathetic trunk ganglion 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. 16.6 Dermatomes • 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 C2 Trigeminal nerve (CN V) C3 C2 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 C3 C4 C5 T1 T2 T3 T4 T5 T6 T7 T2 T1 C5 T2 T1 T8 T9 C7 T10 C6 T11 C5 C8 C5 C7 C8 C5 L1 L2 L3 L4 T12 L1 S2 L1 S3 S3 C6 L2 C7 C8 S4 S5 Co C6 L2 C8 C7 L5 L5 L1 S1 L3 L3 L4 L4 S1 S2 S2 L2 L2 L3 L5 L5 S1 S1 S1 L4 S1 L5 Anterior view L5 Posterior view C6 Page 492 • 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 T1 T2 T3 T4 T5 T6 T7 Typical dermatomal spread of a shingles rash in a 49-year-old man. © Dr. Valerie Dean O’Loughlin Posterior Posterior Fig. 16.5 Deep muscles of back Posterior root Posterior root ganglion Posterior ramus Anterior ramus Anterior root • 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. 16.8 Cervical plexus Anterior rami Cervical plexus branches Other nerves (not part of cervical plexus) • C1-C5 nerves; Innervates muscles and skin of neck Hypoglossal nerve (XII) C1 Atlas Accessory nerve (XI) Segmental branches Lesser occipital nerve Great auricular nerve Transverse cervical nerve Ansa cervicalis Superior root Inferior root Branch to brachial plexus Supraclavicular nerves Phrenic nerve C2 Axis C3 C4 C3 C5 C4 Fig. 16.8 • Phrenic nerve innervates diaphragm Hypoglossal nerve (XII) C1 Atlas Accessory nerve (XI) C2 Segmental branches Lesser occipital nerve Great auricular nerve Transverse cervical nerve Ansa cervicalis Axis C3 C4 C3 Superior root Inferior root Branch to brachial plexus Supraclavicular nerves Phrenic nerve C5 C4 Brachial plexus • Innervates muscles and skin of upper limb, including pectoral girdle Brachial plexus Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions C5 Posterior divisions Cords: posterior, lateral, medial Terminal branches C6 Superior trunk Nerve to subclavius C7 Middle trunk Lateral pectoral nerve Subscapular nerves Lateral cord Posterior cord Musculocutaneous nerve Median nerve Axillary nerve Radial nerve Ulnar nerve C8 T1 Long thoracic nerve Inferior trunk Medial pectoral nerve Thoracodorsal nerve Medial cord (a) Anterior view Fig. 16.9 (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions C5 Cords: posterior, lateral, medial Terminal branches Nerve to subclavius C6 Superior trunk C7 Middle trunk C8 T1 Brachial plexus • 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 Long thoracic nerve originates from Inferior trunk superior trunk (a) Anterior view Fig. 16.9 (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions C5 Cords: posterior, lateral, medial Terminal branches C6 Superior trunk Anterior division Middle trunk C7 C8 Posterior division T1 Brachial plexus • Trunks divide into divisions inferior to clavicle to • anterior division innervates anterior compartment muscles (flexors) • posterior division innervates posterior compartment muscles (extensors) Inferior trunk (a) Anterior view Fig. 16.9 (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions C5 Cords: posterior, lateral, medial Terminal branches C6 Superior trunk Anterior division Middle trunk C7 Posterior division C8 Lateral cord Posterior cord T1 Medial cord Inferior trunk Brachial plexus • 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 (a) Anterior view Fig. 16.9 (left) Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions C5 Cords: posterior, lateral, medial Terminal branches C6 C7 C8 Musculocutaneous nerve Brachial plexus • Cords form 5 terminal branches • axillary • median • musculocutaneous • radial • ulnar T1 Median nerve Axillary nerve Ulnar nerve Radial nerve (a) Anterior view Fig. 16.9 (left) Fig. 16.9 (right) Brachial plexus Clavicle Lateral cord Posterior cord Medial cord Axillary nerve Musculocutaneous nerve Radial nerve Scapula Humerus Ulnar nerve Median nerve Superficial branch of radial nerve Ulna Deep branch of radial nerve Radius Recurrent branch of median nerve Digital branch of median nerve Ulnar nerve Median nerve Deep branch of ulnar nerve Superficial branch of ulnar nerve Digital branch of ulnar nerve (c) Right upper limb, anterior view • 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 Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions C5 Cords: posterior, lateral, medial Terminal branches C6 Superior trunk Anterior division Posterior division • Roots (Reach) • Trunks (To) • Divisions (Drink) • Cords (Cold) • Branches (Beer) Middle trunk C7 C8 T1 Inferior trunk (a) Anterior view Fig. 16.9 (left) Table 16.3a-1 Posterior cord Teres minor Axillary nerve Axillary nerve Deltoid • Motor: deltoid, teres minor • Cutaneous (sensory): superolateral arm Posterior Posterior Copyright © McGraw-Hill Education. Permission required for reproduction or display. Table 16.3a-3 Lateral cord Posterior cord Medial cord Median nerve Pronator teres Flexor carpi radialis Palmaris longus Flexor pollicis longus Pronator quadratus Flexor digitorum superficialis Flexor digitorum profundus (lateral half) Thenar muscles Lateral two lumbricals Anterior Copyright © McGraw-Hill Education. Permission required for reproduction or display. Median nerve • 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 Table 16.3b-1 Lateral cord Biceps brachii Coracobrachialis Musculocutaneous nerve Brachialis Anterior Musculocutaneous nerve • Motor: anterior arm muscles • Cutaneous (sensory): lateral forearm Table 16.3b-3 Posterior Lateral cord Posterior cord Medial cord Radial nerve Lateral head of triceps brachii Long head of triceps brachii Medial head of triceps brachii Brachioradialis Anconeus Supinator Extensor carpi ulnaris Extensor digiti minimi Extensor digitorum Extensor pollicis longus and brevis Extensor indicis Extensor carpi radialis Abductor pollicis longus Radial nerve • Motor: posterior arm, posterior forearm, brachioradialis • Cutaneous (sensory): posterior arm, dorsal aspects of lateral 3 digits Table 16.3c-1 Ulnar nerve Anterior Lateral cord Posterior cord Medial cord Ulnar nerve • Motor: anterior forearm, intrinsic hand muscles • Cutaneous (sensory): dorsal and palmar aspects of pinkie finger and medial half of digit 4 • “Funny bone” nerve Flexor carpi ulnaris Flexor digitorum profundus (medial half) Adductor pollicis Dorsal and palmar interossei Hypothenar muscles Medial two lumbricals Fig. 16.10 Anterior rami Posterior divisions Anterior divisions Lumbar plexus • Divided into 2 divisions • Posterior division L1 Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Lumbosacral trunk (a) Anterior view L2 L3 L4 L5 • Femoral nerve is most important posterior division nerve • innervates muscles of anterior compartment Fig. 16.10 Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Iliacus Femoral nerve Femoral nerve Sartorius Lateral femoral cutaneous nerve L2 L3 L4 Psoas major Pectineus Rectus femoris Vastus intermedius Obturator nerve Vastus medialis Sartorius Vastus lateralis Femoral nerve Saphenous nerve (continuation of femoral nerve) • Motor: anterior thigh muscles • Cutaneous (sensory): anterior and interomedial thigh, medial leg and foot (c) Right lower limb, anterior view b: © The McGraw-Hill Companies, Inc./Photos and Dissections by Christine Eckel Anterior Fig. 16.10 Anterior rami Posterior divisions Anterior divisions Lumbar plexus • Divided into 2 divisions • Anterior division L1 Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Lumbosacral trunk (a) Anterior view L2 L3 L4 L5 • Obturator nerve is most important anterior nerve • innervates muscles of posterior compartment Fig. 16.10 Table 16.4a-3 L2 L3 L4 Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Femoral nerve Obturator externus Lateral femoral cutaneous nerve Obturator nerve Adductor longus Adductor brevis Obturator nerve Adductor longus Adductor magnus Obturator nerve Saphenous nerve (continuation of femoral nerve) • Motor: medial thigh • Cutaneous (sensory): superomedial thigh (c) Right lower limb, anterior view Anterior Gracilis Fig. 16.11 (left) Sacral plexus • innervate gluteal region, pelvis, perineum, posterior thigh, rest of leg and foot • divided into anterior division and posterior division Anterior rami Posterior divisions Anterior divisions L4 L5 Superior gluteal nerve Inferior gluteal nerve Nerve to piriformis Common fibular Sciatic division Tibial division nerve Posterior femoral cutaneous nerve Pudendal nerve (a) Anterior view S1 S2 S3 S4 Fig. 16.11 (right) Fig. 16.11 (right) Sciatic nerve • Largest and longest in body • Tibial and common fibular nerves wrapped in common sheath • split just superior to popliteal fossa Pudendal nerve Posterior femoral cutaneous nerve • innervates posterior leg, sole of foot Tibial nerve Superior gluteal nerve Inferior gluteal nerve Sciatic nerve Common fibular nerve Lateral sural cutaneous nerve Sural nerve Medial plantar nerve Lateral 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. 16.12 Reflex arc 1. Stimulus activates receptor Skin Fig. 16.12 Reflex arc Skin 1. Stimulus activates 2. Nerve impulse receptor travels through sensory neuron to the spinal cord Fig. 16.12 3. Nerve impulse is Reflex arc processed in the integration center by interneurons Nerve impulse is 1. Stimulus relayed to the activates 2. Nerve impulse brain by receptor travels through Skin interneuron sensory neuron to collaterals the spinal cord Interneuron Fig. 16.12 3. Nerve impulse is Reflex arc processed in the integration center by interneurons Nerve impulse is 1. Stimulus relayed to the activates 2. Nerve impulse brain by receptor travels through Skin interneuron sensory neuron to collaterals the spinal cord 4. Motor neuron transmits nerve impulse to effector Interneuron Fig. 16.12 3. Nerve impulse is Reflex arc processed in the integration center by interneurons Nerve impulse is 1. Stimulus relayed to the activates 2. Nerve impulse brain by receptor travels through Skin interneuron sensory neuron to collaterals the spinal cord 4. Motor neuron transmits nerve impulse to effector Interneuron 5. Effector responds to impulse from motor neuron Monosynaptic Reflex Sensory (stretch) receptor Sensory neuron Spinal cord Effector organ Motor neuron Direct communication between sensory and motor neuron (e.g., stretch reflex) • Monosynaptic reflex is simplest • Sensory neuron synapses directly with motor neuron – ex. knee-jerk reflex Fig. 16.14 Stretch reflex • 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 motor nerve endings to extrafusal muscle fibers Intrafusal muscle fiber motor nerve endings to muscle spindle Muscle spindle Sensory nerve endings Polysynaptic Reflex Interneuron facilitates Sensory sensory-motor Spinal cord neuron 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 Sensory receptor Interneuron Motor neuron Effector organ 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
