Vestibular System

Question 1

Where is the vestibular system located?

Answer 1

In the inner ear

Question 2

What is the vestibular system responsible for?

Answer 2

The body’s equilibrium

Question 3

What does it use to transduce physical motion into neural impulses?

Answer 3

Specialized sensory (hair) cells

Question 4

The vestibular labyrinth is composed of what two organs?

Answer 4

otolith organs (utricle & saccule) and the semicircular canals (superior, posterior & horizontal)

Question 5

What are the two types of vestibular hair cells?

Answer 5

Sterocilia, kinocillum (longest process)

Question 6

How does the movement of the hair cells change the membrane potential?

Answer 6

When the stereocilia move toward the kinocillum ==> it depolarizes (excitation) and vice-versa

Question 7

What is the post-synaptic neuron of the hair cells?

Answer 7

The vestibular nerve

Question 8

What are the two otolith organs?

Answer 8

Utricle and saccule

Question 9

What do the otolith organs do?

Answer 9

detect linear movement (translational head movements and head tilts)

Question 10

Each otolith organ contains what?

Answer 10

sensory epithelia (macula), gelatinous layer (hair bundles), fibrous layer (otolithic membrane), otoconia (embedded crystals of calcium carbonate

Question 11

What do the otoconias do?

Answer 11

they make the otolithic membrane heavier than the structures and fluid surrounding it. When the head moves it causes a shift in the membrane relative to the macula which causes the hairs to be displaced and a potential to be generated

Question 12

The utricle detects what kind of translational movements of the head?

Answer 12

The horizontal movements

Question 13

The saccule detects what kind of translational movements of the head?

Answer 13

the vertical movements

Question 14

What is the orientation of the hair bundles present in the utricle?

Answer 14

hair bundles are directed toward the striola and positioned horizontally

Question 15

What is the orientation of the hair bundles present in the saccule?

Answer 15

hair bundles are directed away from the striola and positioned vertically

Question 16

What is the function of the semicircular canals?

Answer 16

specialized for responding to rotations of the head

Question 17

What are the three semicircular canals?

Answer 17

Horizontal (turning left and right), superior ( nodding up and down), posterior (tilting to a side)

Question 18

What are the components of the semicircular canals?

Answer 18

ampulla, cupula, endolymph fluid

Question 19

What is the ampulla?

Answer 19

enlargement at the base of each semicircular canal. Houses the hair cells

Question 20

What is the cupula?

Answer 20

gelatinous mass that the hair bundles extend out into

Question 21

What is the endolymph fluid?

Answer 21

fluid that circulates in the canals. It is through its movement that the hair cells get displaced

Question 22

How do each semicircular canal work in relation to its partner on the other side? How does right work with left?

Answer 22

they work in opposite manner. For example, a head tilt to the right activates the hair cells in the right activates the right posterior canal but inhibits the hair cells in the left posterior canal

Question 23

What are some of the rapid motor movements the vestibular system contributes to?

Answer 23

reflexive eye movements that stabilize gaze, rapid postural adjustments to maintain balance, help with sense of spatial orientation and self-motion

Question 24

Why is the central vestibular processing multisensory?

Answer 24

because it receives visual, cerebellar and proprioceptive inputs

Question 25

What does the vestibular nerve project to?

Answer 25

projects its fibers to the vestibular nucleus in the brainstem which in turn send projections to several brain regions

Question 26

What does the vestibulo-ocular reflex (VOR) do?

Answer 26

VOR produces eye movement that counters head movement to allow the gaze to remain fixed on a particular point

Question 27

What happens to the eyes when the heads turns to the side (left in this case)?

Answer 27

left horizontal canal nerve send signal to vestibular nucleus which sends out two projections: one excitatory to the right abduces nucleus and one inhibitory to the left abduces nucleus. The right abduces nucleus sends an excitatory impulse to the lateral rectus muscle of the right eye and to the medial rectus muscle of the left eye. The left abduces nucleus inhibits the lateral rectus m. of the left eye and the medial rectus m. of the right eye.

Question 28

What does the vestibulo-cervical reflex (VCR) do?

Answer 28

regulates head position by reflex activity of neck muscles in response to stimulation of the semicircular canals following head movement

Question 29

What is the neural pathway in the VCR?

Answer 29

superior canal ==> medial vestibular nucleus ==> medial vestibulospinal tract ==> cervical lower motor neurons ==> activates head/neck muscles

Question 30

What does the vestibulospinal reflex (VSR) do?

Answer 30

initiated by the VCR, VSR causes the extension of the forelimb and the flexion of the hindlimb to stabilize the body and protect against a fall

Question 31

Information from the otolith organs project mainly to what?

Answer 31

to the lateral vestibular nucleus

Question 32

Where do the axons from the lateral vestibular nucleus go?

Answer 32

they descend in the lateral vestibulospinal tract to terminate at the medial levels of spinal cord. They then excite the ipsilateral lower motor neurons and inhibit the contralateral lower motor neurons

Question 33

What does the vestibular-cerebellar pathway do?

Answer 33

plays a critical role in integrating and modulating vestibular signals to enable adaptive changes to VCR, distinguish head tilts from translational movement and distinguish passive movement of head and body from those that are self generated

Question 34

What happens to a blindfolded subject on a rotating chair?

Answer 34

he will perceive that the rotation is slowing and after about 30 seconds, that it has stopped completely even though the chair is still rotating thanks to the desensitization of the hair cells

Question 35

What causes motion sickness?

Answer 35

brain receives conflicting info from the vestibular system, eyes and muscle nerves. Vestibular system reports rocking back and forth while the car seems perfectly stable based on the two other system inputs

Question 36

What is oscillopsia?

Answer 36

condition in which a person with vestibular damage finds it difficult or impossible to fixate on visual targets while the head is moving. Illusion that the environment in moving when head is moving