Chapter 14 Spinal Cord

ganglion

cluster of cell bodies outside of the CNS, enveloped in the epineurium,

sensory nerves

composed only of afferent fibers, are rare, eg olfactory opitic nerves

descending tract

conduct motor impulses down the cord

Functions of Spinal cord

conduction Neural integration locomotion reflexes

gray commissure

connects the left and right sides of the gray matter

mixed nerves

consists of both afferent and efferent fibers, conducts signal in both ways

arachnoid mater

consists of simple squamous epithelium, the arachnoid membrane, adhering to the inside of the dura, and loose mesh of collagenous and elastic ibers spanning the gap between the arachnoid membrane and the pia mater.

the crossing of a nerve or tract from the right side of the CNS to the left or vice versa, is called

decussation

gray matter

dull color, contain little myelin, the somas, dendrites, and proximal parts of the axons of neurons

lateral horn

in the thoracic and lumbar regions, on each side of the gray matter, contains neurons of the sympathetic nervous system, which send their axons out of the cord by way of the anteror root along with the somatic efferent fibers

cervical enlargement

inferior cervical region, where it gives rise to nerves of the upper limbs

lumber cistern

inferior to the medullary cone, the subarachnoid space, occupied by the cauda equina and CSF

lumber enlargement

in the lumbosacral region, where it gives rise to nerves of the pelvic region and lower limbs

poster root

root that converge on the posterior surface of the spinal cord

the outtermost connective tissue wrapping of a nerve is called

the epineurium

dura mater

forms a loose fitting sleeve called the dural sheath around the spinal cord

perineurium

sheath that wraps the fascicles, composed of 20 layers of squamous, epithelium like cells

reflex arc

simple neural pathway used by somatic reflexes, from a sensory nerve ending to the spinal cord or brainstem and back to the skeletal muscle

meningeal branch

small branch that is also part of the division of the nerve as it leaves the intervertebral foramen, reenters the vertebral canal and innervates the meninges, vertebrae, and spinal ligaments with sensory and motor fibers

rootlets

small roots that emerge from the main root to converge and connect to the spinal cord

components of reflex arc

somatic receptors of the skin, muscle or tendon afferent nerve fibers which carries information from the receptors to the posterior horn of the spinal cord integrating center, a neural pool in the gray matter of the spinal cord or brainstem efferent nerve fibers, which originate from the anterior horn and carry motor impulses skeletal muscles, the somatic effectors that carry out the response

dermatome

specific area of the skin that spinal nerves receive sensory input from

the cerebellum receives feedback from the muscle and joint by way of the ___ tracts of the spinal cord

spinocerebellar

when a bone fragment nick the spinal cord, the patient now feels no pain or temperature sensations from that level of the body down, most likely the ____ was damaged

spinothalamic tract

subarachnoid space

the gap between the arachnoid membrane and the pia mater, filled with cerebrospinal fluid,

intercostal nerves

from anterior ramus, travels along the inferior margin of the rib and innervates the skin and intercostal muscles, internal oblique, external oblique, transverse abdominal muscles

posterior ramus

innervates the muscle and joints of the spine and skin of the back

decussation

meaning that the tracts cross over from the left side of the body to the right side of the body or vice versa

coccygeal ligament

the pia mater beyond the medullary cone, anchors the cord to the coccyx

anterior (ventral ) root

the root at the ventral side

posterior/anterior spinocerebellar tracts

travel through the lateral column and carry proprioceptive signals from the limbs and trunk to the cerebellum, first order originate in the muscles and tendons and end in the posterior horn of the spinal cord, second order send their fibers up of the spinocerebellar tracts and end in the cerebellum, the posterior tract travels ipsilaterally to the spinal cord while the anterior tract travel up the contralateral side but then cross back in the brainstem to enter the ipsilateral side of the cerebellum

fascicles

bundles of nerve fibers that are gathered together

medial lemniscus

second order fibers of the gracile and the cuneate when they decussate, tract of nerve fibers that leads the rest of the way up the brainstem to the contralateral thalamus,

spinal nerves

31 pairs 8cervical 12thoracic 5lumber 5sacral 1coccygeal first nerve emerges between the skull and atlas and the other emerge between the intervertebral formina

posterior root ganglion

a swelling past the posterior root which contains the soma of sensory neurons

between the dura mater and the vertebral bone, one is most likely to find

adipose tissue

somatic reflexes

are responses of skeletal muscles, such as the quick withdrawal of your hand from a hot stove or the lifting of your foot when you step on something sharp, they are controlled by the somatic nervous system

tectospinal tract

begins in the midbrain region called the tectum and crosses tot he contralateral side of the midbrain, descends through the brainstem to the upper spinal cord on that side, going to the neck, involved in relfex turning of the head, esp. to sights and sound

upper motor neuron

begins with a soma in the cerebral cortex or brainstem and has an axon that terminates on a lower motor neuron in the brains stem or spinal cord

lateral/medial vestibulospinal tracts

being in the brainstem vestibular nuclei, recieves impulses for balance from the inner ear, lateral passes down the anterior column and control extendose muscles of the limbs so they stiffen and straighten eg. keeping balance, medial splits itno ipsilateral and contralateral fibers that go through the anterior column of both sides and terminate in the neck and plays a role in head position

conduction

bundle of nerve fibers that conduct up and down the body, enables sensory informaton to reach the brain, motor commands to reach the muscles and other effectors,

cauda equina

bundle of nerves roots that occupy the L2-S5, composed of the lumber enlargement and the medullary cone, resembles the horse tail, innervates the pelvic region organs and lower limbs

tracts

bundles of axons, that carry signals from one part of the CNS to another

spinothalamic tract

carries signals for pain, temperature, pressue, tickle, itch, and light or crude touch, first order neurons end on the posterior horn of spinal cord near the point of entry, here they synapse with the second order neuron, which decussate to the opposite side of spinal cord and form the ascending spinothalamic tract, lead all the way to the thalamus, they continue on to the cerebral cortex

gracile fascicules

carries signals from the midthoracic and lower parts of the body, below vertebra T6, it composes the entire posterior column, consists of first order nerve fibrs and travel up the ipsilateral side pf the spinal cord and terminate at the gracile nucleus in the medulla oblongata, carries vibrations, visceral pain, deep and discriminative touch, proprioception

third order neuron

carries the signal the rest of the way to the sensory region of the cerebral cortex, the level of consciousness

corticospinal tracts

carry motor signals from the crebral cortex for precise, finely coordinated limb movements, these fibers form ridges called pyramids on the anterior surface of the medulla oblongata,

ascending tract

carry sensory information up the cord

below l2, the vertebral canal is occupied by a bundle of spinal nerve roots called

cauda equina

neural circuits called ___ in the spinal cord produce the rhythmic muscular contraction of walking

central pattern genertors

regions of the spinal cord

cervical thoracic lumbar sacral regions

the 5 plexus nerves

cervical (neck) brachial (shoulders) lumbar (lower back) sacral (inferior lower back) coccygeal (adjacent to sacrum, coccyx)

white matter

contains an abundance of myelinated axons, which give it a bright, pearly white appearance

second order neuron

continues as far as a gateway called the thalamus at the uper end of the brainstem

medullary cone

conus medullaris, inferior to the lumber enlargement where the cord tapers off

nerve

cord composed of numerous nerve fibers bound together by connective tissue

spinal cord

cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull, passes down the vertebral canal, about 45 cm long and 1.8 cm thick, gives rise to 31 pairs of spinal nerves

pia mater

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

first order neuron

detects the stimulus and conducts a signal to the spinal cord or brainstem

motor nerves

efferent fibers, some are mixed,

anterior (ventral) horns

extend toward the anterolateral surfaces

denticulate ligaments

extensions of the pia that extend through the arachnoid to the dura, anchors the cord and limiting side to side movements

outside the cns, the somas of neurons are clustered in swellings called

ganglion

central pattern generators

group of neurons in the spinal cord that coordinate walking

locomotion

initiate walking, determines the speed, distance, direction,

anterior ramus

innervates the anterior and lateral skil and muscles of the trunk and limbs, the largest division

reflexes

involuntary, stereotyped responses to stimuli, involve the brain, spinal cord, and peripheral nerves

cuneate fasciculus

joins the gracile fascicules at the T6 level, occupies the lateral portion of the posterior column and forces the gracile fascicules medially, same types of sensory as gracile, end in the cuneate nucleus on the ipsilateral side of the medulla oblongata

lower motor neuron

leads the rest of the way tot he muscle or other target organs

central canal

middle of the comissure, collapsed in most areas of the adult spinal cord, remains open in the young,

the intercostal nerves between the ribs arise from whhcih spinal nerve plexus

none of them

the brachial plexus gives rise to all of the following except

obturator

ipsilateral

on the same side of the body

contralateral

opposite side of the body

columns

or funiculi, bundles arranged in three pairs, posterior later anterior

lateral/medial recticulospinal tract

originate in the reticular formation, control muscle of the upper and lower limbs, maintain posture and balance, contain descending analgesic fibers that reduce the transmission of pain signals to the brain

epineurium

outter sheath that wrap around several fascicles that are bundled together, composed of dense irregular fibrous connective tissue and protect the nerve from stretching and injury

quadriplegia

paralysis of all four limbs resulting from lesions above level C5

paraplegia

paralysis of both lower limbs resulting from spinal cord lesions at levels T1 to L1

hemiplegia

paralysis of one side of the body usually resulting not from spinal cord injuries but from a stroke or other brain lesion

which of these is not a region of the spinal cord

pelvic

the ___ nerves arise from the cervical plexus and innervate the diaphragm

phrenic

the ___ ganglion contaisn the somas of neurons that carry sensory signals to teh spinal cord

posterior root

the nonvisual awareness of the bodys position and movements is called

properiception

distal to the intervertebral foramen, a spinal nerve branchs into posterior and anterior

rami

reflex properties

require stimulation, they are quick, involuntary, are stereotyped, occurs in teh same way everytime

visceral reflexes

responses of glands, cardiac muscle, and smooth muscle, controlled by autonomic nervous system

motor innervation of the leg proper comes predominantly from the ___ plexus

sacral

the spinal cord, the somas of the lower motor neurons are found in

the anterior horns

intersegmental reflex

the sensory signal enters the spinal cord at one level and the motor output leaves the cord from a higher or lower level

epidural space

the space between the sheath and vertebral bones, occupied by blood vessels, adipose tissue, and loose connective tissue

tracts, fasciculi

the subdivisions of each column

meninges

the three connective tissue membranes that cover the spinal cord and the brain, from superficial to deep is dura mater, arachnoid mater, and pia mater

all somatic reflexes share all of the following properties

they are monosynaptic

neural integration

they integrate the incoming sensory information and they execute the appropriate output

endoneurium

thin sleeve of loose connective tissue that surround the basal lamina of a nerve fiber

the sciatic nerve is a composite of two nerves, the ___ and ___

tibial, common fibular

spinorecticular tract

travels up the anterolateral system, carries pain from tissue damage, first order enter from the posterior horn and immediately synapse with second order neurons

posterior (dorsal) horns

two that extend toward the posterolateral surfaces of the cord of gray matter

which of these tracts carries motor signals destined for the postural muscles

vestibulospinal tract

anterior corticospinal tract

when a few fibers remain uncrossed on the ipsilateral side of the corticospinal tract in the medulla, they would decussate lower in the spinal cord, so they control contralateral muscles, dissappears by mid thoracic

ipsilateral reflex

when the CNS input and output are on the same side in a reflex arc

monosynaptic reflex arc

when the afferent neuron synapses directly with an efferent neuron, allows for minimal delay and makes it quick

lateral corticospinal tract

when the corticospianl tracts decussate in the lower medulla on the contralateral side of the spinal cord

spinal shock

when the muscles below the level of injury exhibit flaccid paralysis, and because of reflexes because of the lack of stimulation from higher levels of the CNS

contralateral reflexes

when the sensory input enters on one side of the body and the motor output leaves on the opposite side

posterior/anterior ramus

when the spinal nerve emerges from the intervertebral foramen, the nerve divides into these two portions