Spinal Cord & Reflexes

spinal cord span

extends from brain stem to conus medullaris (L1/L2)

cauda equina

nerve bundles inferior to conus medullaris supported by filum terminale (fibrous connective tissue)

cervical enlargement

where spinal nerves exit toward upper limbs

lumbosacral enlargement

where spinal nerves exit toward lower limbs

dorsal roots

bring sensory information into spinal cord

dorsal root ganglia

contain cell bodies of sensory neurons (axons of these neurons from dorsal roots)

ventral roots

contain axons of motor neurons that extend into periphery to control somatic and visceral effectors

denticulate ligaments

prevent lateral movement of spinal cord. extend from pia mater through arachnoid mater to dura mater

spinal meninges

series of specialized membranes surrounding the spinal cord; provide physical stability and shock absorption. layers also contain blood vessels that deliver oxygen and nutrients to the spinal cord

dura mater

tough and fibrous. forms outermost covering of spinal cord. contains dense collagen fibers along longitudinal axis

epidural space

outside of dura mater. made of areolar tissue, blood vessels, protective padding of adipose tissue

arachnoid mater

middle meningeal layer. outer surface covered by simple squamous epithelia

subarachnoid space

region between arachnoid mater and pia mater. filled with cerebrospinal fluid

pia mater

innermost meningeal layer. meshwork of elastic and collagen fibers that is firmly bound to underlying neural tissue

dorsal/posterior gray horn

devoted to sensory information (somatic and visceral are separated)

ventral/anterior gray horn

motor signals to skeletal muscles

lateral gray horn

visceral motor signals (autonomic nervous system)

commissure

axons cross spinal cord

spinal reflexes

rapid, automatic responses to specific stimuli. preserve homeostasis by making rapid adjustments in the function of organs or organ systems

step 1 of reflex arc

arrival of a stimulus and activation of a receptor

step 2 of reflex arc

activation of a sensory neuron

step 3 of reflex arc

information processing in the CNS (may involve interneurons or in simple reflexes, sensory neuron might innervate a motor neuron directly)

step 4 of reflex arc

activation of a motor neuron

step 5 of reflex arc

response of peripheral effector

muscle spindles

the sensory receptors involved in the stretch reflex

intrafusal muscle fibers

bundle of small, specialized skeletal muscle fibers that make up muscle spindles

extrafusal muscle fibers

larger skeletal muscle fibers that surround the muscle spindle. responsible for resting muscle tone and (at greater levels of stimulation) for the contraction of the entire muscle

gamma motor neurons

motor neurons innervating intrafusal fibers