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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.