Vestibular Physiology

Question 1

Balance involves the integration of what?

Answer 1

Vision; proprioception; vestibular system

Question 2

What does the vestibular system sense?

note minor derangements can cause VERTIGO, disorientation, nausea

Answer 2

• Sense the dynamic and static position of the head by detecting linear and angular acceleration.
• Awareness of head position and reflex control of eye movements

Question 3

What is vertigo?

Answer 3

Perception of motion, person or environment when there is no movement.
Differs to dizziness
Often associated with autonomic symptoms, sweating etc

Question 4

Vestibular system inputs and outputs

Answer 4

Inputs: vestibular part of the 8th cranial nerve from the inner ear
Outputs: from the vestibular nuclei to cerebellum, eye, cortex, spinal cord

Question 5

Structure/organisation of the vestibule

Answer 5

Three semicircular canals: Superior(ant): posterior: Lateral (horizontal)

In the central part the utricle (connected to canals) and saccule

Question 6

What do the different parts of the vestibule sense?

Answer 6

Ampulla of semicircular canals: Contain the CRISTAE AMPULLARIS that sense angular acceleration

Utricle and saccule: contains the otolithic organs, the macula sacculus and utriculus that detect static head position and linear acceleration

Question 7

Nerve supply of vestibule

Answer 7

Superior and inferior vestibular nerves in Scarpas ganglion exits as part of the vestibular part of CN8

Question 8

Vestibular nerve divisions and what they innervate

Answer 8

Superior: utricle, ant saccule , horizontal and anterior semicircular canals

Inferior: post saccule and post semicircular canal

Question 9

How are the canals paired? Important physiologically that they operate bilaterally in pairs

Answer 9

The lateral canals of both ear are paired

The anterior canal is paired with the posterior canal of the contralateral ear

Question 10

Sensory cells in the vestibule

Answer 10

Similar to the cochlea in that there are hair cells with stereocilia, main difference is the presence of a large kinocilium. This determines the polarisation of the hair cell

Type 1 (calyx) and 2 hair cells

Question 11

What is inside the cristae ampullaris

Answer 11

In the outer tube containing endolymph there is a swelling at one end. This contains the crista ampullaris, a piece of epithelial that extends into the tube, with the hair cells on it, with a layer of gel extending to the roof called the cupula.

Like a dam

Question 12

What can be said about the hair cell orientation in the cirta ampullaris

Answer 12

They would all be polarised in the same direction, kinocilia all on the same side/plane along the length of the tube.

Question 13

Otolithic organs cell arrangement in urticle and saccule

Answer 13

Hair cells are arranged on macula( utriculus and sacculus), stereocilia project into the otolithic/otoconial membrane which contains calcium carbonate crystals

Question 14

How are the hair cells arranged in the vestibular organs?

Answer 14

All the hair cells are polarised and arranged to be in the same direction. In the canals, one direction. In the urticle, towards the midline (horizontal plane), the saccule away (vertical plane)

Question 15

How are the hair cells stimulated?

Answer 15

A stimulus towards the kinocilium will depolarise the cell, a movement away will hyperpolarise the cell

Question 16

How does the ampulla sense angular acceleration?

Answer 16

The hair cells are stuck in place whereas the fluid (endolymph) in the semicircular canals moves. When you rotate the fluid remains stationary for a moment, causing an apparent flow. This causes a deflection of the cupula and thus the stereocilia in the opposite direction.`

Question 17

How are the otolithic organs (utricle and saccule) detect linear acceleration?

Answer 17

The maculae detect it due to the calcium carbonate in the otoconial membrane. Due to gravity, the mass of membrane, bending the hair cells.

Question 18

Semicircular canal pairs and the sensory output. I.e a head movement in one direction ill do what to the pair?

aVOR

Answer 18

Moving the head one way will cause excitation on one side and inhibition on the other. The brain relies on the coupling to determine the direction of movement.

Question 19

How does vertigo happen from a hair cell firing point of view?

Answer 19

Due to the fact the brain relies on inputs form both sides, if one side has a lesion, there is no input from that side, giving apparent movement at rest

Question 20

VOR

Answer 20

clinical lecture? doesn’t explain well