Chapter 16 Spinal Cord and Spinal Nerves

Spinal cord Atlas Cervical part about 42 to 45 cm in adult Fig. 16.1 Spinal cord Atlas C1 C2 Cervical part C3 about 42 to 45 cm in adult from base of brain to L1 vertebra C4 C5 C6 C7 T1 vertebra C8 T1 T2 T3 T4 Thoracic part T5 T6 T7 T8 T9 T10 T11 Lumbar part T12 Sacral part L1 L2 L3 Cauda equina L4 L5 S1 S2 S3 Filum terminale S4 S5 Co1 (a) Posterior view

Spinal cord Atlas Cervical part T1 vertebra Fig. 16.1 Atlas Spinal cord C1 C2 Cervical part C3 C4 C5 C6 C7 T1 vertebra 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 C8 T1 T2 T3 T4 Thoracic part T5 T6 T7 T8 T9 T10 T11 Lumbar part T12 Sacral part L1 L2 L3 Cauda equina L4 L5 S1 S2 S3 Filum terminale S4 S5 Co1 (a) Posterior view

Nerve numbering Atlas Cervical part Fig. 16.1 Nerve numbering Atlas C1 C2 Cervical part 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) C3 C4 C5 C6 C7 T1 vertebra C8 T1 T2 T3 T4 Thoracic part T5 T6 T7 T8 T9 T10 T11 Lumbar part T12 Sacral part L1 L2 L3 Cauda equina L4 L5 S1 S2 S3 Filum terminale S4 S5 Co1 (a) Posterior view

Spinal cord conus medullaris is end of true spinal cord Fig. 16.1 Spinal cord Spinal cord 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 Conus medullaris Posterior root ganglion Cauda equina Filum terminale (c) Conus medullaris and cauda equina

Spinal cord Gray matter and white matter, as in brain Posterior Gray matter: primarily cell bodies and dendrites White matter: primarily axons White matter

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

Meninges Same meningeal layers as brain Fig. 16.2 Meninges Posterior Spinous process of vertebra Epidural space Dura mater Subdural space Spinal nerve Arachnoid mater Subarachnoid space Intervertebral foramen Pia mater 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 Posterior epidural space site between periosteum of vertebra and dura mater site for giving epidural shot 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) Fig. 16.2 Meninges 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 Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord

Meninges subarachnoid space is filled with CSF Posterior Fig. 16.2 Meninges Posterior Epidural space Dura mater subarachnoid space is filled with CSF site of lumbar puncture Subdural space Arachnoid mater Subarachnoid space Pia mater Spinal cord

Spinal Meninges White matter Gray matter Posterior median sulcus 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

Dermatomes specific segment of skin supplied by a single spinal nerve Fig. 16.6 Dermatomes Trigeminal nerve (CN V) C2 C2 C3 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 C4 C5 C3 C6 C4 C7 C8 C5 T1 T1 T2 T2 C5 C5 T3 T3 T2 T4 T2 T4 T5 T5 T1 T6 T1 T6 T7 T7 T8 T8 T9 T9 T10 C7 T11 C7 T10 C6 C8 T12 C8 C6 C5 T11 C5 L1 L2 T12 L3 L1 L4 S2 L1 S3 S4 S3 S5 C6 C6 Co L2 L2 C7 C8 C8 C7 L5 L5 L1 S1 S1 L3 L3 S2 S2 L2 L2 L4 L4 L3 L5 L5 S1 S1 L4 S1 S1 L5 L5 Anterior view Posterior view

© Dr. Valerie Dean O’Loughlin 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

Multiple spinal nerves may interweave into nerve plexus Fig. 16.5 Posterior Posterior Multiple spinal nerves may interweave into nerve plexus Plexuses innervate body structures (limbs, neck, etc.) Each body structure innervated by extensions from several nerves damage to one nerve or one area of spine may not cause complete loss of sensation or movement Deep muscles of back Posterior root Posterior root ganglion Posterior ramus Anterior ramus divides into nerve plexus

Cervical plexus C1-C5 nerves; Innervates muscles and skin of neck Fig. 16.8 Anterior rami Cervical plexus Cervical plexus branches Other nerves (not part of cervical plexus) C1-C5 nerves; Innervates muscles and skin of neck C1 C1 Hypoglossal nerve (XII) Atlas Accessory nerve (XI) C2 C2 Segmental branches Axis C3 C3 Lesser occipital nerve Great auricular nerve C3 Transverse cervical nerve C4 C4 Superior root Ansa cervicalis C4 Inferior root C5 C5 Branch to brachial plexus Supraclavicular nerves Phrenic nerve

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 Posterior divisions Cords: posterior, lateral, medial Terminal branches C5 C5 Brachial plexus C6 C6 Superior trunk Nerve to subclavius C7 C7 Middle trunk Lateral pectoral nerve C8 C8 Subscapular nerves Lateral cord Posterior cord T1 T1 Musculocutaneous nerve Long thoracic nerve Inferior trunk Medial pectoral nerve Median nerve Thoracodorsal nerve Axillary nerve Medial cord Radial nerve Ulnar nerve Fig. 16.9 (left) (a) Anterior view

Brachial plexus Cords form 5 terminal branches axillary median Anterior rami: C5, C6, C7, C8, T1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions C5 C5 Cords: posterior, lateral, medial Terminal branches Cords form 5 terminal branches axillary median musculocutaneous radial ulnar C6 C6 C7 C7 C8 C8 Musculocutaneous nerve T1 T1 Median nerve Axillary nerve Ulnar nerve Radial nerve (a) Anterior view Fig. 16.9 (left)

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

Table 16.3a-3 Median nerve Lateral cord Posterior cord 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 Medial cord Median nerve Pronator teres Flexor carpi radialis Palmaris longus Flexor digitorum superficialis Flexor pollicis longus Flexor digitorum profundus (lateral half) Pronator quadratus Thenar muscles Lateral two lumbricals Anterior Copyright © McGraw-Hill Education. Permission required for reproduction or display.

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

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

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

Lumbar plexus Anterior rami Posterior divisions Anterior divisions Fig. 16.10 Lumbar plexus Anterior rami Posterior divisions Anterior divisions Divided into 2 divisions Posterior division Femoral nerve is most important posterior division nerve Obturator nerve is most important posterior division nerve L1 L1 L2 L2 Iliohypogastric nerve Ilioinguinal nerve L3 L3 Genitofemoral nerve L4 L4 Lateral femoral cutaneous nerve Femoral nerve L5 L5 Obturator nerve Lumbosacral trunk (a) Anterior view

Femoral nerve innervates muscles of anterior compartment Femoral nerve Fig. 16.10 L2 L3 L4 Iliohypogastric nerve Iliacus Ilioinguinal nerve Femoral nerve Psoas major Genitofemoral nerve Femoral nerve Sartorius Pectineus Lateral femoral cutaneous nerve Rectus femoris Vastus intermedius Vastus medialis Obturator nerve Sartorius Vastus lateralis Femoral nerve Saphenous nerve (continuation of femoral nerve) innervates muscles of anterior compartment (c) Right lower limb, anterior view Anterior b: © The McGraw-Hill Companies, Inc./Photos and Dissections by Christine Eckel

Obturator nerve innervates muscles of posterior compartment Fig. 16.10 Table 16.4a-3 L2 Iliohypogastric nerve L3 L4 Ilioinguinal nerve Genitofemoral nerve Obturator nerve Femoral nerve Lateral femoral cutaneous nerve Obturator externus Adductor longus Adductor brevis Obturator nerve Adductor longus Adductor magnus Gracilis Obturator nerve Saphenous nerve (continuation of femoral nerve) innervates muscles of posterior compartment (c) Right lower limb, anterior view Anterior

Fig. 16.11 (left) Anterior rami Sacral plexus Posterior divisions Anterior divisions L4 L4 L5 L5 innervates gluteal region, pelvis, perineum, posterior thigh, rest of leg and foot S1 S1 Superior gluteal nerve Inferior gluteal nerve S2 S2 Nerve to piriformis S3 S3 Common fibular division Sciatic nerve S4 S4 Tibial division Posterior femoral cutaneous nerve Pudendal nerve (a) Anterior view

Sciatic nerve Largest and longest in body Fig. 16.11 (right) Fig. 16.11 (right) Sciatic nerve Superior gluteal nerve Inferior gluteal nerve 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 Pudendal nerve Posterior femoral cutaneous nerve Sciatic nerve Common fibular nerve Tibial 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

Reflex arc 1. Stimulus activates receptor Fig. 16.12 Reflex arc 1. Stimulus activates receptor 2. Nerve impulse travels through sensory neuron to the spinal cord Skin

Fig. 16.12 Reflex arc 3. Nerve impulse is processed in the integration center by interneurons 1. Stimulus activates receptor Nerve impulse is relayed to the brain by interneuron collaterals 2. Nerve impulse travels through sensory neuron to the spinal cord Skin Interneuron

Fig. 16.12 Reflex arc 3. Nerve impulse is processed in the integration center by interneurons 1. Stimulus activates receptor Nerve impulse is relayed to the brain by interneuron collaterals 2. Nerve impulse travels through sensory neuron to the spinal cord Skin 4. Motor neuron transmits nerve impulse to effector Interneuron

Fig. 16.12 Reflex arc 3. Nerve impulse is processed in the integration center by interneurons 1. Stimulus activates receptor Nerve impulse is relayed to the brain by interneuron collaterals 2. Nerve impulse travels through sensory neuron to the spinal cord Skin 4. Motor neuron transmits nerve impulse to effector Interneuron 5. Effector responds to impulse from motor neuron

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

Stretch reflex Knee-jerk response is a stretch reflex Fig. 16.14  motor nerve endings to extrafusal muscle fibers Intrafusal muscle fiber Stretch reflex  motor nerve endings to 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 Muscle spindle Sensory nerve endings

Polysynaptic Reflex Interneuron facilitates sensory-motor communication (e.g., withdrawal reflex) Sensory receptor Sensory neuron Spinal cord 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 Interneuron Effector organ Motor neuron