Ch 13 Spinal Cord, Spinal Nerves, and Reflexes 2021 PDF

BIO/BMS 318 Anatomy and Physiology I 2021 Ch 13 Spinal Cord, Spinal Nerves, and Spinal Reflexes I. **Overview** (Fig 13-1) A. spinal cord and spinal nerve anatomy along with spinal reflexes (Ch 13) B. cranial nerves and cranial reflexes (Ch 14) II. **Anatomy of spinal cord** (Fig 13-2)...

BIO/BMS 318 Anatomy and Physiology I 2021 Ch 13 Spinal Cord, Spinal Nerves, and Spinal Reflexes I. **Overview** (Fig 13-1) A. spinal cord and spinal nerve anatomy along with spinal reflexes (Ch 13) B. cranial nerves and cranial reflexes (Ch 14) II. **Anatomy of spinal cord** (Fig 13-2) A. superficial anatomy and orientation (Fig 13-2) 1. runs from foramen magnum to lumbar (L) vertebrae, L1-L2 2. spinal cord regions name similar to vertebrae: cervical, thoracic, lumbar, sacral 3. posterior median sulcus 4. anterior median fissure 5. enlargements a. cervical enlargement b. lumbosacral (lumbar) enlargement 6. conus medullaris 7. filum terminale 8. cauda equina 9. spinal cord segments c. 31 spinal cord segments based on origins of spinal nerves d. named by letter and number similar to identifying individual vertebrae 1. cervical (8) 2. thoracic (12) 3. lumbar (5) 4. sacral (5) 5. coccygeal (1) e. each spinal cord segment is associated with dorsal root ganglia, dorsal root, and ventral root 10. dorsal roots and dorsal root ganglia 11. ventral roots 12. spinal nerves f. cervical spinal nerves- name from vertebra immediately [following] it (C1-C8) (7 cervical vertebrae; 8 cervical nerves) g. spinal nerves caudal to first thoracic vertebra have name from the vertebrae [proceeding] it (T1-T12; L1-L5; S1-S5) B. cross sections through spinal cord 1. white matter 2. gray matter 3. ratio of white to gray at different levels of the spinal cord C. **spinal meninges** (Fig 13-3) 1. meningeal layers a. dura mater b. arachnoid layer c. pia mater 2. organization of meningeal layers and spaces from vertebrae to spinal cord a. epidural space b. dura mater c. subdural space d. arachnoid layer e. subarachnoid space f. pia mater g. spinal cord 3. denticulate ligaments (Fig 13-4) and coccygeal ligament 4. medical procedures a. epidural block b. spinal tap 5. meningitis D. **cross-sectional anatomy of spinal cord** (Fig 13-5) 1. posterior median sulcus 2. anterior median fissure 3. central canal 4. **gray matter**: H shape a. **horns** 2. anterior gray horns (somatic motor nuclei) 3. lateral gray horns (only in thoracic and lumbar segments: visceral motor nuclei) III. **Spinal nerves** b. the spinal nerve is formed just outside of the intervertebral foramen c. spinal nerves contain both sensory and motor fibers 1\) sensory fibers from peripheral structures that are traveling to sensory nuclei in the spinal cord 2\) motor fibers from motor nuclei in spinal cord 3\. dermatomes (Fig 13-7) a\. specific region of body surface monitored by single pair of spinal nerves b\. clinical importance D. **nerve plexuses** (Fig 13-9) 3\. major plexuses (no plexus in thoracic region; intercostal nerves instead) a\. cervical plexus b\. brachial plexus c\. lumbar plexus d\. sacral plexus 4\. **cervical plexus** (Fig 13-10) a\. *ventral rami of spinal nerves C1-C5* c\. nerves of cervical plexus 5\. **brachial plexus** (Fig 13-11) 6\. **lumbar plexus** (Fig 13-12) 6. **sacral plexus** (Fig 13-12) a\. *ventral rami from spinal nerves L4-S4* 1\) **sciatic nerve** and its branches: **fibular (peroneal) and tibial nerves** (sciatica - pain over course of nerve) 2\) pudendal nerve d\. other nerves **IF TIME PERMITS; MAY BE COVERED FOR TEST \#4:** **IV. Interneurons of CNS and neuronal pools** A. reflexes are fast, involuntary responses to stimuli B. reflex testing can be used as diagnostic tools to assess the nervous system C. **reflex arc pathway and components (Fig 13-14)** 1\. **receptor** 2\. **sensory nerve** 4\. **motor neuron** 5\. **effector** D. c**lassification of reflexes (Fig 13-15)** 1\. development a\. innate b. acquired reflexes (learned reflexes) 2\. site where information processing occurs a\. spinal reflex b\. cranial reflex 3\. nature of motor response a\. somatic reflexes 1\) stretch reflex 2\) crossed extensor reflex 3\) superficial cord (abdominal, cremaster, plantar reflexes) 4\) corneal reflex (mediated by cranial nerves) 5\) gag reflex (mediated by cranial nerves) b\. visceral (autonomic) reflexes 1\) pupillary reflex 2\) ciliospinal reflex 3\) salivary reflex 4\. complexity of neural circuit a\. monosynaptic reflex b\. polysynaptic reflex E. **stretch reflex (monosynaptic reflex)** ( Fig 13-14) 1\. [sensory receptor] = muscle spindle 2\. [sensory (afferent) neuron] 3\. sensory neuron [synapses] with motor neuron in spinal cord (anterior gray horn) 4\. [motor (efferent) neuron] (large, type A (α) motor neuron) 5\. [effector] = skeletal muscle fibers (extrafusal fibers) 6\. examples: knee jerk (patellar) reflex; achilles/ankle jerk reflex F. **polysynaptic reflexes** (Fig 13-14) 1\. responses include a\. several muscle groups b\. interneurons produce excitatory or inhibitory stimuli/responses 2\. tendon reflex a\. monitors tension in muscles during muscle contraction to prevent tearing of tendons b\. sensory receptors = Golgi tendon organs c\. sensory neurons stimulate inhibitory interneurons in that innervate motor neurons 3\. **withdrawal reflexes** a\. stimulus: pain (touch, pressure) b\. flexor (withdrawal) reflex 1\) flexor muscles move limb from stimulus 2\) opposing extensor muscle of same limb must relax (reciprocal inhibition; antagonist muscles inhibited) 4\. **crossed extensor reflexes** a\. contralateral reflex vs ipsilateral reflex b\. works along with flexor reflex c\. axons of interneurons also cross to other side of spinal cord and stimulate motor neurons that control extensor muscle of opposite leg d\. opposite leg straightens to support body 5\. other polysynaptic reflexes: postural and motor reflexes G. Superficial cord reflexes (Fig 13-17) Plantar reflex (negative Babinski reflex) - adults - flex (curl) toes Babinski sign (positive Babinski reflex) - infants - fan toes