Chaper 12 Anatomy Lecture Exam

Spinal Cord and Spinal Nerves

spinal cord enlargements

cervical and lumbosacral give rise to the spinal nerves of the limbs

cauda equina

roots of nerves that extend from the spinal cord

conus medullaris

cone-like region inferior to the lumbosacral enlargement

meninges

connective tissue membranes that surround the brain and spinal cord

dura mater

forms a thecal sac that surrounds the spinal cord

attaches to the rim of the foramen magnum and ends at the level of the second sacral vertebra

arachnoid mater

thin whispy meningeal layer deep to the dura mater

pia mater

the deepest meningeal layer that is bound tightly to the surface of the brain and spinal cord

epidural space

between the bony vertebral canal of the vertebral canal and the dura mater

blood vessels, areolar tissue, fat

subdural space

between the arachnoid mater and the dura mater, serous fluid

subarachnoid space

between the arachnoid mater and the pia mater, cerebrospinal fluid

spinal cord consists of…

gray matter and white matter

anterior median fissure

deep cleft partially separating right and left halves

posterior median sulcus

deep cleft partially separating right and left halves

the three columns of the spinal cord

lateral, dorsal, and ventral

white matter in the spinal cord

consists of myelinated axons forming tracts and located superficially (surrounding gray matter)

tracts

composed of axons ascending to the brain or descending from the brain

axons within a given tract (fascicules) carry the same type of information (sensory or motor)

fasciculi

funiculi subdivided into tracts in the white matter

gray matter

consists of neurons, neuron cell bodies, dendrites, and axons

dorsal (posterior) horns of gray matter

contains sensory axons that synapse with interneurons

ventral (anterior) horns of gray matter

contain the neuron cell bodies of somatic motor neurons

lateral horns of gray matter

contain the neuron cell bodies of autonomic (visceral) motor neurons

gray and white commissures

connect each half of the spinal cord

central canal

located in the center of the gray commissures

roots

spinal nerves arise as rootlets then combine to form roots

located along the dorsal and ventral surfaces of the spinal cord

dorsal root

contains afferent/sensory axons

dorsal root ganglion

collection of cell bodies of the sensory neurons

ventral root

contains the efferent/motor axons

spinal nerve

dorsal and ventral roots merge laterally, contains both sensory and motor axons

why are spinal nerves considered mixed nerves?

pass both sensory and motor information in both directions of the spinal cord and body

reflex arc

sensory receptor, sensory neuron, interneuron in the CNS, motor neuron, and effector organs

sensory receptors

respond to stimuli and produce action potentials in sensory neurons

sensory neurons

propagates action potentials to the spinal cord

interneurons in the CNS

synapse with sensory neurons and with motor neurons

motor neurons

carry action potentials from the CNS to effector organ

effector organs

respond to the action potential, usually muscles or glands

somatic reflexes

mediated through the somatic nervous system and includes responses that: remove the body from painful stimuli, keep the body from suddenly falling, cause movement because of external forces

autonomic reflexes

mediated through the autonomic nervous system and are responsible for maintaining variables within their normal ranges like bp, blood CO2 levels, and water intake

golgi tendon reflex

controls muscle tension and prevents excessive tension that could damage tendons, acting to relax the muscles

stretch reflex

controls muscle length and maintains posture

withdrawal reflex

protects the body from painful or harmful stimuli (pulling hand away from hot surface)

crossed extensor reflex

when a withdrawal reflex in initiated in one limb, the crossed extensor reflex causes extension of opposite lower limb

reciprocal reflex

causes relaxation of extensor muscle when flexor muscle contracts, involved in withdrawal and stretch reflex

endoneurium

surrounds axons and their schwann cell sheath

perinuerium

surrounds axon groups

epinerurium

surround the entire nerve

dermatome and its clinical importance

an area of skin supplied by sensory nerve fibers from a single spinal nerve dorsal root and are essential for identifying spinal cord injury levels, diagnosing radiculopathy, and tracing herpes zoster

raml

spinal nerves branch to form the dorsal and ventral rami

dorsal ramus

innervates deep/intrinsic muscles responsible for movement of the vertebral column and the C.T. and skin near the midline of the back

thoracic region ventral ramus

form intercostal nerves that innervate the intercostal muscles and the skin over the thorax

plexuses

organization produced by the ventral rami of spinal nerves

cervical plexus

ventral rami of C1-C4

brachial plexus

ventral rami of C5-T1

musculocutaneous, radial, axillary, ulnar, and median

lumbar plexus

ventral rami of L1-L4

sacral plexus

ventral rami of L4-S4

coccygeal plexus

ventral rami of S4-S5

ventral and dorsal rami

dorsal: smaller branches that go posteriorly to supply the muscles and skin of the back

ventral: larger branches that go anteriorly to supply the limbs and body wall

brachial plexus

axillary nerve

laterally rotates the arm and abducts the arm

radial nerve

extends and flexes elbow, extends and abducts wrist, extends fingers and thumb, extends and adducts wrist, supinates forearm and hand

musculocutaneous nerve

flexes shoulder, flexes elbow and supinates forearm and hand, and flexes elbow

ulnar nerve

flexes and adducts wrist, flexes fingers, adducts thumb, controls hypothenar muscles, flexes metocarpophalangeal joints, and adducts and abducts fingers

median nerve

pronates forearm and hand, flexes and abducts wrist, flexes wrist and fingers, controls thumb muscles, controls thenar muscles, flexes metacarpophalangeal joints, and extends interphalangeal joints

obturator nerve

adducts thigh, rotates thigh laterally, adducts thigh and flexes knee

femoral nerve

flexes and extends hip and knee

tibial nerve

plantar flexes foot, flexes foot, flexes knee, extends hip and adducts thigh, extends hip and flexes knee

common fibular nerve

extends hip and flexes knee