Vestibular System

Question 1

Provides sense of equilibrium
Fluid-filled sacs and ducts located in the temporal bone.
Hair cells in the otolith organs (utricle and saccule) respond to linear accelerations of head.
Hair cells of the ampullae in the semicircular canals respond to head rotations
Works closely with other sensory systems to maintain stable body position.

Answer 1

Vestibular System

Question 2

within the membranous labyrinth is an extracellular fluid and is unusual because it contains a relatively high concentration of K+, but low levels of Na+ and Ca2+ ions.

Answer 2

Endolymph

Question 3

Hair bundles project from the apical surface of hair cells into:

Answer 3

endolymph.

Question 4

The basolateral hair cell membrane is bathed in ________ (regular extracellular fluid).

Answer 4

perilymph

Question 5

Structure of Vestibular Organ

Answer 5

membranous labyrinth
3 perpendicular canals+, utricle,and saccule

+=rotation
*= linear accel

Question 6

Hair cells in the otolith organs (utricle and saccule) respond to linear accelerations of head.
Hair cells of the ampullae in the semicircular canals respond to :__________

Answer 6

head rotations (angular acceleration).

Question 7

Line of polarity reversal

Answer 7

In the utricle the axes of polarity of hair cells reverse direction along a central region of the epithelium called the striola.

In the saccule the hair bundles are oriented facing away from the striola.

Question 8

In the utricle the axes of polarity of hair cells reverse direction along a central region of the epithelium called the striola.

In the saccule the hair bundles are oriented facing______ from the striola.

Answer 8

away

Question 9

Endolymph moves the cupula and stimulates hair cells in the _______. Hair bundles within the canal all have the same orientation. Vestibular nerve carries signals to the brain.

Answer 9

crista ampullaris

Question 10

Even at rest the vestibular nerve fires action potentials. During a rotation in the excitatory direction, firing rate will: ___

Answer 10

increase and then adapt (due to endolymph inertia)

Question 11

cupula

Answer 11

Jelly like

providing the sense of spatial orientation. Located within the ampullae of each of the three semicircular canals.

Question 12

the sensory organ of rotation located in the semicircular canal of the inner ear. The function is to sense angular acceleration and deceleration

Answer 12

crista ampullaris

Question 13

Motion sensed by Cupula

Answer 13

Acceleration
Deceleration
Does not sense continued motion (Adaptation)

Question 14

Ion channels (permeable to cations) are gated by _______ which connect adjacent stereocilia in the hair bundle.

Answer 14

tip links

At rest ~ 10 % of the mechano-sensitive channels are open.

Question 15

Pushing the hair bundle in the excitatory direction (towards the tallest cilia) opens more channels, _________ from endolymph enter and depolarize the hair cell.

Answer 15

K+ and Ca2+

Hair Cells are mechano-transducers

Question 16

Pushing the bundle away from the tallest cilia closes channels and __________the hair cell.

Answer 16

hyperpolarizes

Hair Cells are mechano-transducers

Question 17

Vestibular Hair Cell Types

Answer 17

Type 1 and Type 2

Question 18

Vestibular Ocular Reflex (VOR)

Answer 18

Shortest Reflex in body
Enables stable visual field during head movement
Oculomotor nuclei in brainstem
Leads to Nystagmus (involuntary eye movements)

Question 19

During a head rotation the vestibular system signals how fast the head is moving and the oculomotor system responds to keep visual field stable.

Answer 19

Vestibular Ocular Reflex (VOR)

Question 20

Movement of accessory structure modulates release of __________ from hair cells onto afferent nerve terminals.

Answer 20

glutamate

Question 21

Vestibular neurons (VIIIth nerve) carry head velocity and acceleration signals to __________in the brainstem.

Answer 21

vestibular nuclei

Question 22

Efferent fibers originate from _______- and synapse onto hair cells or their afferents. Efferent stimulation can excite or inhibit afferent firing.

Answer 22

brainstem

Question 23

Vestibular Nuclei Subdivided into:

Answer 23

superior, medial, lateral, descending.

Question 24

Vestibular Nuclei- Superior and medial receive fibers mostly from

Answer 24

semicircular canals (gaze control).

Question 25

Vestibular Nuclei- Lateral nucleus (Deiter’s nucleus) receives input from canals and otoliths and is involved in:

Answer 25

postural reflexes.

Question 26

Vestibular Nuclei- Descending nucleus receives mostly otolith input and integrates ____________

Answer 26

vestibular and motor signals

Question 27

Angular accel mechanism

Answer 27

Cupula moves more quickly than endolymph (it is being dragged through) and bends Cilia on hair cells

bent towards kinocilium: depol/ excit
bent away: hyperpolar/ inhibit

Question 28

Nystagmus

Answer 28

Head rotation causes eyes to move slowly in opposite direction

When limit of eye movement is reached, eyes rapidly snap back (nystagmus), then move slowly again

*occurs in the same direction of head movement