Chapter 16 Spinal Cord and Spinal Nerves Fig

Chapter 16 Spinal Cord and Spinal Nerves

Fig. 16. 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L 3 L 4 L 5 S 1 S 2 S 3 S 4 S 5 Atlas Cervical part T 1 vertebra Thoracic part Lumbar part Sacral part Cauda equina Filum terminale Co 1 (a) Posterior view Spinal cord • about 42 to 45 cm in adult • from base of brain to L 1 vertebra

Fig. 16. 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L 3 L 4 L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Atlas Cervical part Spinal cord T 1 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 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L 3 L 4 L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Atlas Cervical part T 1 vertebra Thoracic part Lumbar part Sacral part Cauda equina Filum terminale (a) Posterior view Nerve numbering • Spinal nerves numbered based on vertebra • C 2 exits between C 1 and C 2 vertebrae • C 8 exits between C 7 and T 1 • below C 8, named for vertebra above exit spot (T 6 nerve exits below T 6 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 • Gray matter and white matter, as in brain • Gray matter: primarily cell bodies and dendrites • White matter: primarily axons Posterior Gray matter White matter

Table 16. 1 d C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 L 3 L 4 Atlas Cervical part T 1 vertebra Cervical Thoracic part Thoracic Lumbar part Sacral part L 5 S 1 S 2 S 3 S 4 S 5 (a) Posterior view Lumbar Sacral

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. 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 C 2 Trigeminal nerve (CN V) C 3 C 2 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 C 3 C 4 C 5 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 2 T 1 C 5 T 2 T 1 T 8 T 9 T 10 C 6 T 11 C 5 C 7 C 8 C 5 L 1 L 2 L 3 L 4 T 12 L 1 S 3 S 3 C 6 L 2 C 7 C 8 S 4 S 5 Co C 6 L 2 C 8 C 7 L 5 L 1 S 1 L 3 L 4 S 1 S 2 L 2 L 3 L 5 S 1 S 1 L 4 S 1 L 5 Anterior view L 5 Posterior view C 6

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 T 1 T 2 T 3 T 4 T 5 T 6 T 7 Typical dermatomal spread of a shingles rash in a 49 -year-old man. © Dr. Valerie Dean O’Loughlin

Posterior Fig. 16. 5 Deep muscles of back Posterior root ganglion Posterior ramus Anterior ramus divides into nerve plexus • 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

Fig. 16. 8 Cervical plexus Anterior rami Cervical plexus branches Other nerves (not part of cervical plexus) • C 1 -C 5 nerves; Innervates muscles and skin of neck Hypoglossal nerve (XII) C 1 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 C 2 C 3 Axis C 4 C 3 C 5 C 4

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

Brachial plexus Anterior rami: C 5, C 6, C 7, C 8, T 1 Trunks: superior, middle, inferior Anterior divisions C 5 Posterior divisions Cords: posterior, lateral, medial Terminal branches C 6 Superior trunk Nerve to subclavius C 7 Middle trunk Lateral pectoral nerve Subscapular nerves Lateral cord Posterior cord Musculocutaneous nerve Median nerve Axillary nerve Radial nerve Ulnar nerve C 8 T 1 Long thoracic nerve Inferior trunk Medial pectoral nerve Thoracodorsal nerve Medial cord (a) Anterior view Fig. 16. 9 (left)

Anterior rami: C 5, C 6, C 7, C 8, T 1 Trunks: superior, middle, inferior Anterior divisions Posterior divisions Cords: posterior, lateral, medial C 5 Terminal branches C 6 C 7 C 8 Musculocutaneous nerve Brachial plexus • Cords form 5 terminal branches • axillary • median • musculocutaneous • radial • ulnar T 1 Median nerve Axillary nerve Ulnar nerve Radial nerve (a) Anterior view Fig. 16. 9 (left)

Table 16. 3 a-1 Posterior cord Teres minor Axillary nerve Deltoid • Motor: deltoid, teres minor • Cutaneous (sensory): superolateral arm Posterior Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display.

Table 16. 3 a-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 © Mc. Graw-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. 3 b-1 Lateral cord Biceps brachii Coracobrachialis Musculocutaneous nerve Brachialis Anterior Musculocutaneous nerve • Motor: anterior arm muscles • Cutaneous (sensory): lateral forearm

Table 16. 3 b-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 Anconeus Supinator Extensor carpi ulnaris Extensor digiti minimi Extensor digitorum Extensor pollicis longus and brevis Extensor indicis Brachioradialis 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. 3 c-1 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 L 1 Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral femoral cutaneous nerve Femoral nerve Obturator nerve Lumbosacral trunk (a) Anterior view L 2 L 3 L 4 L 5 • Femoral nerve is most important posterior division nerve • Obturator nerve is most important posterior division nerve

Fig. 16. 10 Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Iliacus Femoral nerve Sartorius Lateral femoral cutaneous nerve L 2 L 3 L 4 Psoas major Pectineus Rectus femoris Vastus intermedius Obturator nerve Vastus medialis Sartorius Vastus lateralis Femoral nerve Saphenous nerve (continuation of femoral nerve) • innervates muscles of anterior compartment (c) Right lower limb, anterior view b: © The Mc. Graw-Hill Companies, Inc. /Photos and Dissections by Christine Eckel Anterior

Fig. 16. 10 Table 16. 4 a-3 L 2 L 3 L 4 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) • innervates muscles of posterior compartment (c) Right lower limb, anterior view Anterior Gracilis

Fig. 16. 11 (left) Sacral plexus • innervates gluteal region, pelvis, perineum, posterior thigh, rest of leg and foot Anterior rami Posterior divisions Anterior divisions L 4 L 5 Superior gluteal nerve Inferior gluteal nerve Nerve to piriformis Common fibular division Sciatic Tibial division nerve Posterior femoral cutaneous nerve Pudendal nerve (a) Anterior view S 1 S 2 S 3 S 4

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 Skin 1. Stimulus activates receptor

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

Fig. 16. 12 3. Nerve impulse is processed in the integration center by interneurons Nerve impulse is 1. Stimulus relayed to the activates 2. Nerve impulse brain by receptor travels through interneuron sensory neuron to collaterals the spinal cord Reflex arc Skin 4. Motor neuron transmits nerve impulse to effector Interneuron

Fig. 16. 12 3. Nerve impulse is processed in the integration center by interneurons Nerve impulse is 1. Stimulus relayed to the activates 2. Nerve impulse brain by receptor travels through interneuron sensory neuron to collaterals the spinal cord Reflex arc Skin 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