CNS Exam II

units IV & V

superior boundary of spinal cord

foramen magnum/cervical spinal nerve

inferior boundary of adult spinal cord

disc between vertebral levels L1-2

how many spinal nerves are there?

31 pairs, 62 in total

Bell-Magendi law states that

dorsal roots contain sensory fibers and ventral roots are motor fibers

PNS structures in vertebral canal

roots/rootlets, spinal nerves and their rami

CNS structures in vertebral canal

spinal cord

SAME DAVE

sensory-afferent, motor-efferent; dorsal-afferent, ventral-efferent

cervical nerves C1-C8 all exit

above vertebrae but C8 exits below C7 and above T1

C1 exits

between occiput and atlas

C4 exits at

IVF (intervertebral foramen) between C3 and C4

C8 exits at

IVF between C7 and T1

Thoracic nerves T1-T12 exit

below corresponding vertebrae

Lumbar nerves L1-L5 exit

below corresponding vertebrae

Sacral nerves S1-S4 exit

dorsal and ventral sacral foramina

sacral nerve S5 exits

at sacral hiatus

coccygeal nerve Co1 exits

sacral hiatus and may be missing

at birth the Co1 cord level is at the same level as

L1-L3 vertebral level

in 90% of people by adulthood the Co1 cord level is found at the

L1-L2 vertebral level

the tapering end of the spinal cord is called the

conus medullaris

what stage of embryonic development is the spinal cord and vertebral column approximately the same length?

the first 3 months

T/F after 3 months of embryonic development the spinal cord lengthens more rapidly than the vertebral column

F- the vertebral column lengthens more rapidly than the spinal cord during the rest of gestation (after 3 months)

cauda equina

the roots of the lumbar, sacral, and coccygeal nerves that run for an extended distance below the cord, down through the lumbar cistern; resembles a horse’s tail

quadriplegic

when C8 and/or above is damaged, still have function of upper extremities

paraplegic

when T1 and below is damaged, little to no function of upper extremities

grey matter

dense concentration of neuron cell bodies, thick dendritic mats near cell bodies, synaptic activity, no myelin, “grey h in snow”, support glial cells, dense capillary beds

white matter

dense concentration of axons (neuron fibers), info traveling through, not all myelinated, interfascicular oligodendrocytes, less blood vessels than grey matter

T/F both grey and white matter are present in all levels of the spinal cord

T

T/F the spinal level and cord level always match up

F- they match well in cervical but not so much further down, discrepancy gets larger the further down cord goes

central canal

cranially continuous with central canal of M.O. and 4th ventricle, inferiorly expands in conus medullaris as terminal ventricle, it’s a small and insignificant channel near center of spinal cord

dorsal horns function

sensory/afferent information

lateral horns function

pre-ganglionic parasympathetic fibers

ventral horns function

motor/efferent information

funiculus

longitudinal bundle of white matter fibers that can be anatomically observed

rexed laminae I

thin cap over dorsal horn

rexed laminae II

important pain and temperature reception center called substantia gelatinosa, lateral spinothalamic tract

rexed laminae III&IV

filled with group of cell bodies called the nucleus proprius, anterior spinothalamic tract, carries touch, pressure, tickle (anything but pain)

rexed laminae V

cervical area only, complex of fibers and cell bodies in cervical region called formatio reticularis- send axons to contralateral spinothalamic tracts to thalamus, found at all cord levels

rexed laminae VI

not present at every cord level, most anterior aspect of dorsal horn, if present (T1-L2, S2-S4) no lateral horn

rexed laminae VII

lateral horn included when present, many descending tract fibers synapse with neurons in this lamina, nucleus dorsalis (clarke’s nucleus) present C8-L3, posterior spinocerebellar tract, corticospinal fibers

laminae VIII

medial aspect of lateral horn

laminae IX

class alpha motor neurons, contains largest/fastest conducting motor neurons in body, most skeletal muscle motor innervation neurons here, why ventral horn called somatic motor horn

laminae X

surrounds central canal, contains anterior and posterior gray commisures, mostly unmyelinated

fasciculi

bundles of functionally related axons within a funiculus, fibers associate with one another by surface proteins during development, nerve cell adhesion molecules (NCAM’s)

T/F tracts are observable by general staining techniques

F

how fasciculi (tracts) were identified

animal experiments- DRG destruction, wide animal range-mammals (cats, chimps, etc.), modern aids- HRP, triated amino acids, PET scanners, human pathologies(strokes, etc.)

tract anatomical review

sensory input enters spinal cord as dorsal root ganglion axons at dorsal lateral sulcus → most axons synapse in dorsal gray horn laminae → secondary axons from dorsal gray laminae branch of either alone or together as collateral branches

secondary axon and collateral branch pathway

go to ventral horn of original segment → cross to an opposite horn at same segmental level → some run between cord segment levels (intersegmentals) ipsilaterally or contralaterally, some may project to higher brain centers (often associated together to form ascending fasciculi) → descending fasciculi

descending fasciculi

fibers from higher brain centers descending to generally end in the cords lamina VII, VIII, IX

how many recognized fasciculi are in the body?

over 2 dozen

fasciculi tract characteristics

3-dimensional, ascending and descending are bilateral, not every cord levels will have all tracts represented

fasciculi gracilis

slender, in medial aspect of dorsal funiculus, in all cord levels, fibers synapse in nucleus gracilis of MO

fasciculi cuneatus

wedge shape, lateral aspect of dorsal funiculus, T5/6 (chest) up, fibers synapse in nucleus cuneatus of MO

fasciculi gracilis and cuneatus functions

2-point touch discrimination, fibratory and kinesthetic sensations/ conscious proprioception- ability to perceive consciously the position and movement of body’s parts

romberg’s test

single-most misinterpreted test - testing for gracilis/cuneatus path (especially gracilis) 2-point touch/sensory, patient stands feet together with eyes closed and see if they have trouble keeping balance

orientation of gracilis and cuneatus

contralateral- ascending info to cerebrum from right will go to the left cerebrum and vice versa, all descending info from right cerebrum will go to left extremity and vice versa; 3-neuron pathway in which the 2nd neuron crosses over

lateral and anterior spinothalamic tracts

formed by axons coming from cell bodies in gray horns of cord therefore dorsal root fibers bringing sensory information into cord must synapse in gray matter of cord, synapse in VPL nuclei of thalamus, may be considered together as one continuous spinothalamic tract even though they have separate functions, when together make up large part of anterolateral system

lateral spinothalamic tract

located in lateral funiculus, present in all cord levels, carries pain and temperature info, 2nd neuron crosses immediately

anterior spinothalamic tract

located in anterior funiculus, present in all cord levels, carries light touch/pressure, 2nd neuron crosses slowly

if there’s a lesion on the left side of the spinal cord it will affect sensing pain and temperature on which side of lower body?

it will affect the right because pain/temp is lateral spinothalamic and that crosses immediately

lesions in spinothalamic tract lead to

analgesia- loss of pain sensation and thermoanaesthesia- loss of temperature sensation on opposite side of body

anterior spinocerebellar tract

along the periphery of lateral funiculus, most fibers cross in the cord then cross again as they enter cerebellum, fiber origins are mostly in lumbrosacral cord’s gray laminae, fibers terminate in cerebellum via superior cerebellar peduncle, sends to cerebellum input on general state of gross movements of lower body and general activity of what is about to happen from motor neurons in part of cord

posterior spinocerebellar tract

along periphery of lateral funiculus, most fibers do not cross, fiber origins are from cell bodies in nucleus dorsalis (C8-L3) tract not found below L3, fibers terminate in cerebellum via inferior cerebellar peduncle, proprioceptive input for dealing mainly with fine movements from what has happened in the muscle itself

posterior spinocerebellar that enters below L3

hitchhikes on gracilis tract up to L3 where nucleus dorsalis is present then follows posterior spinocerebellar original pathway

posterior spinocerebellar that enters above C8

ascends to M.O. and accessory cuneate nucleus where it then follows cuneocerebellar tract into cerebellum

cuneocerebellar tract

fine movement proprioceptive fibers from pectoral gridle and extremity enter cervical cord and ascend to synapse in M.O.’s accessory cuneate nucleus, fibers that leave the nucleus form cuneocerebellar tract, ascend to cerebellum through inferior cerebellar peduncle, does for hands and arms what nuclei dorsalis does for lower body legs and feet

spinoreticular terminates in

reticular formation

spinocortical terminates in

cerebral cortex

spinoolivary terminates in

inferior olivary nucleus

spinovestibular terminates in

vestibular nucleus

spinopontine terminates in

pons

spinotectal terminates in

tectum

corticospinal tracts

left and rigth side of cord each receive about 1 million corticospinal fibers, 85-95% of these enter lateral corticospinal fasciculi, fiber diameters range 2-25 microns majority being small/moderate diameter and lightly myelinated, only axon fibers that begin in cerebral cortex and run uninterrupted to spinal cord, decrease in fibers in each tract as they descend the cord(55% cervical, 20% thoracic, 25% lumbo/sacral), many fibers synapse with neurons in lamina VII→many lamina VII neurons find synapse with neurons in lamina IX, less than 3% lateral corticospinal axons terminate directly on lamina IX neurons mostly Betz cells

anterior corticospinal tract

in anterior funiculus, only about 5-15% of total corticospinal fibers, most fibers cross in spinal cord after they terminate, terminates by mid thoracic cord level (T6), function unclear

“small ants collect food after grasshoppers order them, but terminate halfway and don’t know what to do”

lateral corticospinal tract

in lateral funiculus, contains 85-95% mass of corticospinal fibers, most fibers cross in pyramids of medulla oblongata, runs entire length of spinal cord, function critical for initiating and accomplishing precise skilled voluntary muscle movements “big pyramids run all of egypt”

Lower motor neurons

neurons that originate in spinal cord or brain stem and extend fibers into the PNS to innervate somatic musculature

upper motor neurons

neurons from higher brain centers that influence so-called lower motor neurons, corticospinal tract fibers are good examples, entirely in CNS

UMN lesions

reduction or absence of voluntary movement, hyperreflexia, increased muscle tone, clonus(arm bounces when trying to resist pressure bc uncontrollable flexion), cerebral palsy

LMN lesions

reduction or absence of voluntary movement, hyporeflexia/areflexia, hypotonia/decreased muscle tone and atrophy, muscle fibrillations/fasciculations, inability to produce movement, lower extremity paralysis, polio

pyramidal neurons

upper motor neurons that are involved with initiation of skilled voluntary movements, pyramidal fibers are corticospinals, have conscious control

extrapyramidal neurons

complex of upper motor neurons that mostly originate in brain stem and extend down to cord, generally influence posture, muscle tone, enhance reflexes thus allowing voluntary movements to be smooth and effective “fine-tune coordination”

tectospinal tract

originates in superior colliculus of midbrain’s tectum, fibers cross as they descend, most fibers terminate in upper 4 cervical cord levels

function of tectospinal tract

extrapyramidal postural reflex enhancement dealing with sight and auditory stimuli, accomplished by adjustments to the trapezius and steinocleidomastoid muscles of the neck, moving the head via the IX cranial nerve

rubrospinal tract

originates in red nucleus (nucleus ruber) of midbrain’s tegmentum, fibers cross in midbrain as they descend, reaches all cord levels

function of rubrospinal tract

fibers are strongly influenced by cerebellum and cerebral cortex for extrapyramidal muscle tone control primarily in contralateral hand and foot flexor musculature (brachialis, biceps brachii, flexor digitorum, etc) “bc bro’s flex”

vestibulospinal tract

extrapyramidal fibers, originates in lateral part of vestibular nucleus located in M.O. (deiter’s nucleus), fibers do not cross (ipsilateral), runs entire length of cord along antero-lateral funicular junction

function of vestibulospinal tract

muscle and postural adjustment primarily in ipsilateral extensor musculature while inhibiting flexors, maintains proper orientation in falling/maintaining equilibrium, and enhances spinal reflex capability

reticulospinal tracts

heart, blood pressure and respiratory rates and rhythms are carried to the cord through these tracts, it may also serve as an alternative pathway if corticospinal tract fibers are destroyed

medial (pontine) reticulospinal tract

anterior funiculus, originates in pons tegmentum, mostly uncrossed, terminates at all cord levels in medial parts of ventral horn or intermediolateral cells

lateral (medullary) reticulospinal tract

lateral funiculus, originates in medulla oblongata, mostly uncrossed, terminates at all cord levels in medial parts of ventral horn or intermediolateral cells

fasciculus proprius

spinospinal fiber cell bodies originate in cord and axons terminate in cord, fibers usually extend short distances up or down the cord, may or may not cross, vastly important in coordination for spinal reflexes, first fibers to be myelinated in fetus

dorsolateral tract (of lissauer)

between rexed lamina I and posterior lateral sulcus of cord, primarily composed of small diameter collateral fibers off posterior root axons, collaterals run short distances up or down cord and synapse in gray horns

what can cause CNS lesions?

stroke is most common, trauma, infections, tumors, etc.

what vertebral levels are a common site for severe injury and why?

C5/C6 and T12/L1 because of vertebral motility at these points and cord is maximum size within

brown-sequard syndrome

total loss of either right or left side of spinal cord (hemisection/cut halfway through)

multiple sclerosis

results in destruction of CNS myelin- targets interfascicular oligodendrocytes, more common in females 2:1, onset most commonly between ages 20-40, symptoms commonly remit and relapse, remissions become less common and of shorter duration as condition progresses

amyotrophic lateral sclerosis

results in destruction of UMNs and LMNs principally in lateral corticospinal tracts, males afflicted twice as much as females, onset usually after age 45, localized weakness or clumsiness usually first sign/symptom, condition progresses until diaphragm is involved and death results from inability to breathe

Rhombencephalon parts

myelencephalon, metencephalon

myelencephalon includes the

medulla oblongata

metencephalon includes the

pons and cerebellum

the brain stem is made of

medulla oblongata, pons, midbrain