Section 3 Vestibular System Flashcards by Tedman McMahon

Vestibular fxns:

stabilization of eye position, perc of body rotation and translation, visual and postural vertical perc

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Disorders of the vestibular system:

Meniere’s disease, Benign Paroxysmal Positional Vertigo (BPPV)

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BPPV is more common as:

you age

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What signal the static position of the head with respect to gravity and its linear acceleration?

Utricle and saccule

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What signals rotation and angular acceleration of the head?

Semicircular canal

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Names of the 3 loops of the semicircular canal:

ant, pos, and lateral

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What regions of the ear contain hair cells?

Cochlea? (check)

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The utricle detects:

linear accelerations and head-tilts in the horizontal plane.

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The saccule detects:

linear accelerations and head-tilts in the vertical plane.

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Where are the axons of the utricle located?

Trick Question. There are none

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Explain the transmission of info from the hair cell in the utricle.

Synaptic vesicles in body of hair cell release glutamate on 8th nerve afferents which send info about these organs to the brain

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How many 8th nerve afferents are connected to each hair cell?

1 in the images in slides

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At which end of the hair cells are the hair bundles?

Apical end

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What are the tips of the hair cells embedded in?

Otolithic membrane, gelatinous structure overlying the hair cells

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Fxn of otoconia:

to add extra weight to the structure

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What are found on the otolithic membranes in the utricle?

Otoconia (Ca carbonate crystals)

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Endolymph has a high conc of what ion?

K+, positively charged

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What are the hair bundles surrounded by?

endolymph

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2 different ECF involved w hair cells:

Endolymph, high K+ and positively charged (top of the structure) and perilymph, high Na++ and low K+, surrounding the hair cell bodies

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Effects of tilting head:

tilt membrane that is mechanically coupled to the bone that surrounds the structure

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What causes distortion of the otolithic membrane?

weight of the otoconia when tilting head

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Linear acceleration:

distortion of the hair cell with respect to body, epi moves in same direction as head bc they are mechanically connected, bending of the hair bundles

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What causes the hair uncles to bend during acceleration?

the inertia of the heavy crystals that accelerate more slowly than the hair cell bodies

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How many kinocilium per hair strucutre are there?

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Kinocilium is aka:

true cilium

Where are kinocilium located?

all vestibular hair cells

How are the hair stereocilia arranged?

Same height L to R - polarized, short to tall in other direction, affects how each of the hair cells work

Fxn of step-like arrangement of stereocilia of the hair cell:

How moves of upper part of structure triggers electrical changes to go to the CNS (check)

About how many stereocillia are there?

What system is the kinocilium related to:

vestibular

How are the stereocilia arranged?

Step-like

How are adjacent stereocilia of the hair cell attached?

Tip links

Where do tip-links attach to the stereocilia?

locations of mecahno receptor channels

Fluid bathing the stereocilia:

endolymph, K+ is the predominant ion that will be flowing in (Ca as well, but mainly K)

What 2 ions can flow into the stereocilia?

Ca and K

What is the extracellular fluid of the inner ear?

endolymph

Disorders of the endolymph:

disruption of endolymph production or hair cells fxn

Disruption of endolymph production can lead to:

Vertigo, vomiting, hearing impairment

What can cause the disruption of endolymph production?

inflammation of the inner ear

Meniere's disease:

disruption of the hair cell fxn, attacks w no warning, last hours

Possible causes of Meniere's disease:

head trauma, virus, or rise in endolymph volume due to hole in membrane separating endolymph and cochlea fluids OR improper endolymph drainage

What is the hair cell potential?

-50mV, bc cell is slightly depolarized due to the tugging on membrane that open mechanoreceps allowing K to enter

How do the hair cells activate its afferents?

NTs

When will there be no volvtage change in hair cell receps?

Orthogonal (R angle) tilt

When is the 8th nerve firing rate at its greatest?

When the hair fibers are flowing in the opposite direction of the 8th nerve., largest space bw stereocilia opening more channels

When is the 8th nerve firing rate at its least?

hair fibers tilted in direction of the 8th n.

How is the 8th n. firing when there is no movement of the hair cell?

active signal that says that nothing much is happening

How can direction be conveyed via the hair cells. How do the cells transmit this info differently?

When not moving there is an intermediate firing rate, when pushed in either direction the firing rate will either increase or decrease making directional differentiation easy

Firing rate of a hair cell at rest:

100 Hz

What NT is used by the hair cells to transmit info?

glutamate

How are the tip links connected in the orthogonal directon (into the plane of the page)?

They aren't

The utricle can detect head tilt in any direction away from:

vertical

How are the hair cells at different angles in the utricle affected with a tilt of the head?

some depolarize, some hyperpolarize, some not affected

T or F? Hair cells are more sensitive in one direction.

What structure looks just like the utricle but is oriented vertically in the upright head?

Saccule

When does the sacculus sense most effectively?

When the head is on its side

What do the semicircular canals respond to?

Head rotation

How many canals are there on each side?

3: 1 horizontal (L R turning of head), 1 ant and 1 pos duct, both upright, 90' to each other (X,Y,Z axis)

T or F? Semicircular canals respond to linear and static tilt.

F. head rotation only

Specialized region that contains hair cells:

ampulla

Hair bundles that stick out are assoc w:

cupula (flexible)

What allows for endolymph to participate in the signaling of changes in movement?

it is fluid and not mechanically coupled to the outside structures (i.e. the cupola is coupled to membrane)

What bends in the endolymph with moves?

cupula

A turn to the R depolarizes all the hair cells in the:

R horizontal canal

In which manner are movements of variable speed transmitted?

in a graded manner

T or F? A turn to the R depolarizes ALL the hair cells in the R horizontal canal.

This/these structure(s) has hair bundles of only one orientation while this/these structure(s) have hair bundles oriented in all directions.

semicircular canal, saccule and utricle

Where are the larger stereocilia located?

toward the back of the head

When you turn your head to the R will the tip links in the L canal be brought closer together or spread further apart?

closer

When you turn your head to the R will more or less K enter the cilia of the L canal? More or less firing?

less K coming in, less positive charge, and less firing

Turn head to the R:

L horiz canal hyperpol, R horiz canal dep

Turn head to the L:

L horiz canal depol, R horiz canal hyperpol

What will the 8th n. afferent increase or decrease its firing rate in response to?

direction and rate of motion

What does redundancy of info from the 2 sides allow for?

vestibular compensation

2 clases of symptoms related to damage to vestibular canals, otoliths, and/or vestibular n. on one side of the head:

static (seen in absence of head moves) and dynamic (seen w head moves)

T or F? Peripheral damage to the vestibular system can be compensated for.

Immediate effects of damage to vestibular canals, otoliths, and/or vestibular n. on one side of the head:

problems w balance, posture, gait, and eye moves

T or F? There is a quick recovery time with vestibular compensation.

F. gradual

T or F? Different symptoms of vestibular compensation recover at different rates.

Example of when vestibular compensation is important:

when there are more subtle changes in vestibular input such as a loss of a few hair cells

Likely sites for where compensation occurs:

vestibular nuclei and cerebellum

What fraction of the hair cells die off with aging?

About 1/4

Faction of adults, 65+ that fall each year:

1/3

Leading cause of injury or death for people 65+:

falls

vestibular issue that rises in frequency in the 40's:

bening parxysmal position vertigo (BPPV)

Cause of BPPV:

detachment of otoconia in the utricle, allowing them to enter a semicircular duct

What causes a person w BPPV to feel like they are spinning?

lodging of Ca carbonate crystal in a position that causes them to incorrectly activate hair cells of the semicircular canal

Tx for BPPV:

Otolith Repositioning Procedure

When does severe vertigo occur for pts with BPPV?

head moves

How is vestibular info distributed?

Widely in the thalamus

Vestibular info can combined with (what?) to maintain balance.

visual and proprioceptive input

What sort of visual and proprioceptive input does the thalamus receive?

visual response to optokinetic stimuli (large field, moving stimuli) and prop to neck m. moves

Large-field, moving stimuli:

Optokinetic stimuli

Somatosensory lesion:

sensation that vertical objects are tilted toward the side of the lesion

What do cells in the somatosensory cortex respond to?

some cell: head rotation, others: head tilt

What is the most common sensation in the cortical vestibular responsive areas?

rotation

T or F? There are only a couple of areas of the brain yielding vestibular sensations.

F many areas

Major vestibular area (concentration) in the cortex:

temporo-parietal and parietoinsular cortex

T or F? Some cells in the cortical vestibular responsive areas have a purely vestibular response.

T. Others are multimodal (visual, prop, vestibular)

posterior T cortical lesions:

impair vestibular-derived saccades

Insulotemporal infarctions may lead to:

a tilted perception of visual vertical and to rotational vertigo in stroke pts

What does an impairment of eye responses indicate?

vestibular signal not working correctly