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51 Cards in this Set

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What two parts comprise the vestibulo-cochlear nerve?
Vestibular part: hair cells synapse on vestibular nerve fibers with their cell body in Scarpas/ vestibular ganglion

Auditory part: hair cells synapse on auditory nerve fibers with cell body in Spiral ganglion.

These two nerves combine to form the VIIIth nerve which passes thru skull in the internal auditory meatus
What are the otolith organs and what function do they serve?
otolith organs = saccule and utricle

-serve in static balance (head tilt) and linear acceleration
What is the function of the semicircular canals?
sense head rotation in different planes
Utricle

-what is the receptor surface in the utricle called?
macula ; composed of hair cells, support cells, and nerve fibers.; arranged HORIZONTALLY; hair cells switch direction at STRIOLA

--sitting on top of hair cells is otolithic membrane, a gelatinous mass with calcium carbonate crystals

each hair cell has 40-70 stereocilia and one kinocilium in graded array.
What is the sensory organ in the semicircular canals
The sensory organ is the ampullary crest; hair cells are within the cupula so rotational acceleration causes shearing of hair cells one way or other due to endolymphatic flow

within ampullary crest, all hair cells are aligned the same way.
What are the functional pairs of semicircular canals?

what is meant by functional pairs
functional pairs:
L and R horizontal
L anterior and R posterior
R anterior and L posterior

they are pairs because they are both in the same plane. therefore one will be depolarized while the other gets hyperpolarized in a certain plane
Vestibular nuclei; how many?

what do they receive inputs from?
There are four vestibular nuclei on each side:

they all receive inputs from (to a degree):
1. vestibular organs,
2. contralateral vestibular nuclei,
3 fastigial nucleus and floccular-nodular lobe of cerebellar cortex,
4. proprioceptive info from neck and posture m.
outputs of the vestibular system?

hint. four.
1. SC
2. oculomotor nuclei
3. reticular formation
4. nucleus of solitary tract
What does the vestibular nerve give direct input to?
the nodulus and fastigial nucleus of cerebellum (via juxta-restiform body)
What does the lateral vestibulo-spinal pathway do?
Lateral vestibulo-spinal pathway:
head/body tilt or linear acceleration activates antigravity m. to counteract tilt/acceleration
-ie fall asleep in class!! :)
What does the medial vestibulo-spinal pathway mediate?
mediates vestibulo-colic reflex: rotation of body activates neck musculature to turn head in direction opp the rotation of body.
What does the vestibulo-ocular reflex (VOR) depend on? the integrity of what pathway?
MLF; MLF fibers coordinate action of lateral rectus (VI) and medial rectus (III)

also depends on integrity to vestibular nuclei, flocculonodular lobe as well as mlf
what is nystagmus?
normal physiological nystagmus is fast eye mvmt following slow mvmt of vestibular ocular reflex.

fast mvmt in direction of head rotn --fn is to return eye to center of orbit
clinically do you report the fast or slow phase of nystagmus?
fast
what is the difference between rotatory and caloric tests?
rotatory is for determine performance of functional pair of semicircular canals.

caloric determines fn of just one side using warm or cool waterplaced on external auditory meatus

COWS = cool nystagmus in opp direction; warm = same direction
vestibular disorder due to toxic substance?
hair cells loss : aminoglycoside antibiotics
BPPV (Benign Paroxysmal Positional Vertigo)
BPPV: vertigo and nystagmus for brief periods; often after sleeping
due to otoconia (crystals) becoming lodged in semicircular canal
Meniere's disease
DEBILITATING
--due to increased endolymphatic Pressure
-severe, recurrent episodes (4+hours) of severe vertigo, nystagmus, and auditory symptoms
-loss of receptor cells if not controlled
what is blood supply to vestibular nuclei?
PICA

--wallenberg syndrome if blocked --nystagmus and vertigo
vestibular neuritis
inflammation of vestibular nerve, due to viral infection

inc vertigo and nystagmus

lasts more than 24 hours
What do we perceive sound frequency as?
we perceive sound frequency as pitch.

humans sensitive 20-20,000Hz
What do we perceive amplitude as?
loudness / intensity

we hear sounds over a broad range of sound pressures, about a factor of a MILLION; use the decibel to express this broad range
what is the task of the peripheral auditory system?
to convert airborne mechanical waves into electrochemical activity in nerve cells.
What are the two middle ear m. and what are they innerv. by?
stapedius - CN VII (Bell's palsy!)

tensor tympani - CN V
Pathologies of middle ear.
otitis media = ear infection

otosclerosis = abnormal bone growth in middle ear. reduces hearing.
The oval window, against which the stapes pushes against communicates with what part of the cochlea?
scala vestibuli - contains perilymph
Which part of the cochlea contains the hair cells?
the scala media - endolymph filled (from stria vascularis)

hair cells sit on basilar membrane.
What separates the scala vestibuli from the scala media?
Reissner's membrane
What separates scala media from scala tympani?
basilar membrane

the scala tympani borders round window
what organ rests on the basilar membrane?
organ of corti ---contains sensory hair cells; in each cross section 1 inner hair cell : 3 outer hair cells
--hair cell stereocilia project into endolymph of scala media (contacting tectorial membrane)
do the outer or the inner hair cells make the most contact with the auditory nerve fibers?
inner !! ~95% of auditory nerve fibers connected to inner. supply majority of input to cNS

the outer hair cells only ~5%
--fn = cochlear tuning and sensitivity of inner hair cells
How are hair cells in the cochlea stimulated?
hair cells in the cochlea are stimulated when the basilar membrane is driven up or down due to the difference in pressures between the scala vestibuli and tympani
--deflection of stereo cilia in one direction causes change in ionic conductance at apical surface of cell (ie mvmt of membrane upward causes deflection of hair bundles so that channels open --cell becomes depolarized! K+ flux in.
--shearing in other direction closes excessive leak channels hyperpolarizing cell
where are high frequencies deflected the most in the cochlea?
near the base! where basilar membrane is stiffer

low freq = apex

therefore basilar membrane is TONOTOPICALLY organized
energy-utilizing mechanisms are responsible for full sensitivity and frequency selectivity of hair cells
--ie outer hair cells have what special function?
OHCs are contractile: shorten with each sound-induced depolarization
--since they are connected to both basilar and tectorial membrane; their contraction sharpens mechanical tuning of basilar membrane

particularly susceptible to noise damage and aminoglycoside antiobiotics --damage. causes sign loss of hearing sensitvity and freq selectivity
each side of brain? analyzes sounds predominantly in the ________ sound field?
CONTRALATERAL.
is there always a tonotopic organization of auditory nuclei?
yessss
what projects down to cochlea and outer hair cell contractile aparatus to modulate its function?
the olivo-cochlear pathway from accessory nuclei of superior olivary nucleus
where do fibers of neurons in the spiral ganglion project to?
ipsilateral cochlear nucleus;
dorsal cochlear nucleus and ventral cochlear nucleus
what does the dorsal cochlear nucleus do?
analyzes vertical sound localization
what does the ventral cochlear nucleus do?
analyzes timing of sounds
what does the superior olivary nucleus do?
compares timing from two ears or intensity difference
IMPT in locating source

accessory nuclei project to cochlear via olivo-cochlear pathway (modulate contractile ability of outer hair cells)
what does the inferior colliculus do?
integrates info ; input from contralateral side is dominant but some ipsi info
medial geniculate body --receives ascending input from?
brachium of inf colliculus
-projects to auditory cortex
-descending input from auditory cortex modifies activity of MGB
Where is the primary auditory cortex located?
area 41; pull apart lateral sulcus (on superior part of temporal lobe)
organized TONATOPICALLY
--low frequency sounds--rostrolaterally
--high freq sounds - caudomedially

also analysis of complex features
what are the association auditory cortices?
area 42 and 22

22 speech processing; other speech areas = 39 and 40 aka wernicke's area
middle cerebral a can damage these areas impairing speech comprehension
what is tinnitus?
hearing sound when there is no sound; due to trauma of outer hair cells and CNS hyperexcitability
what is it called when a hearing disorder is due to age?
presbycusis
what is conductive hearing loss?
vibrations associated with sound are not transmitted mechanically properly.
disorder with outter or middle ear
what is sensorineural loss?
vibrations in inner ear are not converted into electrical potential or are not transmitted to CNS
-disorder of hair cell or auditory nerve.

-cochlear and vestibular str of inner ear and VIIIth n are often involved in pathological processes together
what is acoustic neuroma?
aka vestibular schwannoma
-sensorineural loss
--tumor begins in vestibular component of CN VIII
-if grows --facial n dysfunction
cochlear prostheses can be used if?
auditory nerve fibers are in tact