vestibular physiology

Question 1

structures that detect static head position and linear acceleration

Answer 1

• utricle and saccule of the otolithic organ
• macula sacculus
• macula utriculus

Question 2

nerves supplying to vestibular system and pathway

Answer 2

superior and inferior vestibular nerve with cell bodies in scarpas ganglion exits as part of vestibulocochlear nerve in internal acoustic meatus

Question 3

what does the superior division of the vestibular nerve innervate

Answer 3

• utricle
• anterior part of saccule
• lateral and anterior semicircular canals

Question 4

what does the inferior division of the vestibular nerve innervate

Answer 4

• posterior part of saccule

- posterior semicircular canal

Question 5

pairing of canals

Answer 5

left anterior canal = right posterior canal

right anterior canal = left posterior canal

left lateral = right lateral

Question 6

difference between cochlear and vestibular sensory cells

Answer 6

• referred to as type 1 and 2 (not IHC & OHC)

- large kinocilium

Question 7

what occurs within the vestibular system when we move our head

Answer 7

causes the calcium carbonate crystals (inside utricle and saccule) to move as they are heavier than the gel surrounding it. When they move they physically pull on the hair cells they are attached too causing an AP

Question 8

what detects angular acceleration

Answer 8

cristae ampullaris

semicircular canals

Question 9

how are cells depolarized?

Answer 9

fluid pushes against cupula and causes movement of stereocilia, bending them towards the stereocilium - results in neurotransmission

Question 10

how are cells hyperpolarized?

Answer 10

when the stereocilia are bent away from the stereocilium it will inhibit neurotransmission

Question 11

how does hair cell transduction occur?

Answer 11

(same mechanically-gated ion channel process as cochlea)

1. K+ comes in and depolarizes the cell
2. Ca2+ enters through calcium voltage-gated channels
3. Ca2+ activates K+ channels allowing K+ to exit
4. cell repolarizes

Question 12

polarization of otolithic organs

Answer 12

(different to hair cells)

utricle - polarized towards boundary

saccule - polarized away from boundary

Question 13

vestibular ocular reflex

Answer 13

we move our head in one direction and our eyes will move in the opposite to obtain gaze stabilization

Question 14

role of sensory cells

Answer 14

they’re polarized and provide direction and acceleration of movement

Question 15

How is angular acceleration

detected?

Answer 15

Vestibular hair cells are polarised and arranged so that they are aligned in the same direction.
As the head moves, the endolymph remains stationary for a moment because of its inertia. Thus
there is an apparent flow of endolymph in the opposite direction to the head movement –>
causes a deflection of the cupula and sensory hair cell stereocilia.
Displacement of stereocilia towards the kinocilium causes hair cell depolarisation and increase in
vestibular nerve discharge. Displacement of sterocilia away from kinocilium results in cell
hyperpolarisation and decrease nerve discharge.
Sensory cells in the pairs of semicircular canals are oriented in opposite directions. Thus rotation
of head in one direction causes excitation of sensory cells and increased afferent activity on that
side, and a decrease in activity on the other side. The brain relies on the comparison in discharge
patterns from both sides to determine direction and acceleration of movement.

Question 16

How is linear acceleration

detected?

Answer 16

Otolitic organs = utricle and saccule are gravity receptors and linear acceleration detectors. They
are oriented at right angles; utricle horizontal, saccule verticle. They contain sensory hair cells in
a matrix of supporting cells, arranged in Macula sheets. The stereocilia of the hair cells project
into the otolithic membrane. Overlying this is a gelatinous mass that contains otoconia (crystals of
calcium carbonate).
The otoconia increase the mass of the membrane covering the hair cells & give it greater inertia.
They provide info on the static position of the head + linear acceleration in vertical & horizontal
plane. Since the hair cells of each macula are oriented in diff directions, the tilt of the head will
depolarise some cells and hyperpolarise others in the same side.