chapter 13 spinal cord, spinal nerves, and somatic reflexes

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conduction, locomotion, reflexes

spinal cord functions

conduction

bundles of fibers passing information up and down the spinal cord connecting different levels of the trunck with each other and with the brain

locomotion

walking; involves repetitive coordated actions of several muscle groups

reflexes

involuntary stereotyped responses to stimuli.

4 regions of the spinal cord

cervical; thoracic; lumbar; sacral

cervical enlargement

nerves to upper limb

lumbar enlargement

nerves to pelvic region and lower limbs

medullary cone

cord tapers to a point inferior to lumbar enlargement

cuada equina

bundle of nerve roots that occupy the vertebral canal from L2-S5.

terminal filum

fibrous strand of pia mater that extends beyond the medullary cone within the lumbar cistem

dura mater; arachnoid mater; pia mater

what are the three menengies

dura mater

forms loose fitting sleeves around spinal cord dural sheath

arachnoid mater

line the dura mater and loose mesh of collagenous and elastic fibers

pia mater

delicate, translucent membrane that follows the contours of the spinal cord

spina bifida

congenital defect in which one or more vertebrea fail to form a complete vertebral arch for enclosure of the spinal cord

grey matter; white matter

cross section anatomy of the spinal cord

grey matter

find synapses; thinking part of the brain; un myelinated

white matter

myelinated axons; transmission process information

dorsal horn

grey matter; sensory

ventral horn

grey matter; somatic motor

lateral horn

automatic; sympathetic

axon tract

subdivisions of each column of the spinal cord

ascending tract

carry snesory information up the spinal cord

descending tract

carry motor information down the spinal cord

first order neurons

recieves info from receptor transmitt signal to spinal cord or brainstem

second order neurons

carries that info from first order neurons up the spinal cord to the thalmus

third order neurons

carries info to specific regions; to the sensory region of the cerbral cortex

spinothamic tract

lateral and anterior column; sensation of ligh touch, tickle, temperature, pain and pressure

spinoreticular tract

lateral and anterior column; sensation of pain from tissue injury

conticospinal tract

descending tract; finely coordinated limb movements; in lower medulla

reticulospinal tract

descending tract; balance and posture; subconscious movement; controls muscles of upper and lower limbs

poliomyelitis

caused by poliovirus; destroys motor neurons in brainstem and anterior horn of spinal cord; muscle pain, weakness and loss of some reflexes; fecal contamination of water

ALS

lou gehrig diseas; distruction of muscular atrophy; astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid

nerve

bundle of neurons (axons) bound by connective tissue

spinal nerves

how spinal cord communicates with the rest of the body

schwann cell

ensheath nerves of peripheral nervous system

endoneurium

cover each fiber thin sleeve of loose connective tissue

perineurium

wraps fascicles

epineurium

outter covering the whole nerve

ganglion

cluster of neurosomas outside the CNS.

spinal nerves

mixed nerves 31 pair; formed by dorsal and ventral roots

anterior ramus

innervates the anterior lateral skin and muscles of the trunck

posterior ramus

innervates the muscles and joints in that region of the spine and the skin of the back

dermatone

regions of our skin that recieve sensory input from specific pair spinal nerves

dorsal root ganglion

contains the somas of sensory neurons carrying signals tot he spinal cord ; 6-8 roots that enter posterior horn of cord

sensory (afferent) nerves

carry signals from sensory receptors to the CNS

motor (efferent) nerves

carry signals from CNS to muscles and glands

mixed nerves

consists of both afferent and efferent fibers conduct signals in two directions

nerve plexuses

cervical; brachial; lumbar; sacral; coccygeal

cervical plexus

in the neck C1-C5; phrenic nerve

brachial plexus

near shoulder; upper and lower limbs; median nerve, radial nerve; ulnar nerve

lumbar plexus

lower back; L1-L4; supplies abdominal wall and anterior thigh and genatalia; femoral nerve

sacral plexus

in the pelvis; L4,L5 and S1 to S4; supplies remainder of lower trunck and lower limb; sciatic nerve(longest largest nerve in body)

spinal reflexes

quick, involuntary, stereotyped reactions of glands or muscle to stimulation

spinal reflex arc

somatic receptors; afferent nerve fibers; intergrating center; efferent nerve fibers; skeletal muscle

muscle spindle

stretch receptors embedded in skeletal muscles

stretch reflex

when a muscle is stretched it fights back and contracts which maintains increased tonus, making it stiffer than unstretched muscles; helps maintain equilibruim and posture ex. patellar tendon reflex arc.(knee jerk)

tendon reflex

in response to excessive tensions on the tendon; inhibits muscle from contracting strongly; moderates muscle contraction before it tears a tendon or pulls it loose.

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