Anatomy of the Spinal Cord Cervical enlargment lumbar enlargement conus medullaris Cervical enlargment (C 7 -C 8 ), lumbar enlargement (T 11 -T 12 ), conus medullaris (L 1 -L 2 ) dorsal root ganglia Each spinal segment has a pair of dorsal root ganglia Dorsal rootsventral roots Dorsal roots vs. ventral roots spinal nerve mixed nerves Sensory & motor nerves combine to form spinal nerve (classified as mixed nerves) Named for vertebra superior to nerve (except cervical)

Spinal Meninges Provide stability & shock absorption Dura mater Dura mater forms outer covering Epidural space Epidural space between dura mater & vertebra Arachnoid mater subarachnoid space Arachnoid mater surrounds subarachnoid space cerebrospinal fluid (CSF) Contains cerebrospinal fluid (CSF) Pia mater Pia mater bound to spinal cord

White matter vs. gray matter Gray Matter horns Forms a butterfly shape; horns of gray matter on each side of spinal cord Sensory motor nuclei Sensory vs. motor nuclei Posterior gray horns anterior gray horns lateral gray horns Posterior gray horns vs. anterior gray horns vs. lateral gray horns (only thoracic & lumbar)

White Matter posterior anterior lateral white columns Each side of spinal cord divided into posterior, anterior & lateral white columns Ascending tracts descending tracts Ascending tracts vs. descending tracts

Epineurium perineurium endoneurium Epineurium vs. perineurium vs. endoneurium dermatomes Skin surfaces monitored by dermatomes Examine & know process of sensory information collection & motor commands in Figure 13-7 (pg 426 – 427)! Nerve plexuses Nerve plexuses—spinal nerves converge Cervical brachial lumbar sacral plexus Cervical vs. brachial vs. lumbar vs. sacral plexus

neuronal pools Billions of interneurons in CNS organized into neuronal pools Neuronal pools circuit patterns: Divergence convergence serial processing parallel processing reverberation Divergence vs. convergence vs. serial processing vs. parallel processing vs. reverberation

The Reflex Arc Know the 5 steps of a reflex arc Classification of Reflexes innate acquired Development of reflexes (innate vs. acquired) somatic visceral Nature of response (somatic vs. visceral) monosynaptic polysynaptic Complexity of circuit (monosynaptic vs. polysynaptic) spinal cranial Processing sites (spinal vs. cranial)

Monosynaptic Reflexes Little delay between sensory input & motor output Stretch reflex Stretch reflex triggers skeletal muscle contraction through stretching of receptors Patellar reflex Patellar reflex (knee-jerk) Postural reflexes Postural reflexes maintain upright posture

Polysynaptic Reflexes Interneurons control motor neurons that activate several muscle groups Tendon reflex Tendon reflex prevents tearing of tendons Withdrawal reflex Withdrawal reflex triggered by pain or pressure Flexor reflex Flexor reflex causes muscles to flex & move away from stimulus Crossed extensor reflex Crossed extensor reflex complements flexor reflex