22: Vestibular

Question 1

What are the semicircular canals responsible for?

Answer 1

• Sensitive to angular acceleration during head rotation.

- Aligned in 3 axes (as there are 3 semicircular canals, with it sensing acceleration in one plane

Question 2

Describe the ampulla

Answer 2

-The ampulla can be described as a “swelling” on the canal which is filled with endolymph.

There is a network of vestibular haircells (similar to hair cells of cochlea)

Question 3

Describe the hair cells of the ampulla and their effects

Answer 3

The hair cells have stereocilia which project from the apical surface into the cupula

The displacement of the cupula would result in the displacement of the hair cells

Question 4

Describe the discharge rate of the vestibular nerve.

Answer 4

Movement of hair cells in one direction (right) increases action potential frequency in the afferent nerve activated by the hair cell.

Movement in the opposite direction (left) decreases the rate relative to the resting state

Question 5

Describe how movement is sensed

Answer 5

• Sensed by fluid motion in the semicircular canals
• These work in pairs
• The stereocilia on the left are more active
• The stereocilia on the right are less active

Question 6

Describe the role of thr Utricle and Saccule-Otolith organs-

Answer 6

Detect linear acceleration (as opposed to angular)

Question 7

Describe the utricle

Answer 7

Utricle approximately horizontal when standing

-Information on horizontal linear acceleration

Question 8

Describe the Saccule

Answer 8

Saccule approximately vertical when standing

-Information on vertical acceleration (gravity).

Question 9

Describe the features of the otolith organs

Answer 9

The Otolith organ has Otoconia which are stones of calcium carbonates which act as “weights”

If you accelerate towards the right, the mass and inertia would drag towards the left (and vice versa)

The changes the constitute in the rate of firing

Question 10

Describe the central pathways of the vestibular system

Answer 10

Axons project to vestibular nuclei in brainstem

Information from there used to; 1) stabilise eyes (via oculomotor nuclei)

2. Stabilise the head (via input to neck muscle motorneurons)
3. Maintain balance (via pathways to cerebellum and spinal cord)

Question 11

What are some vestibular functions (s)

Answer 11

• Reflexes to compensate for head movement and the perception of motion in space
• Maintenance of upright posture
• Conscious awareness of position/movement/acceleration (linear and rotational) of the head and the body

Question 12

What are some vestibular disorders? (3)

Answer 12

• Vertigo -caused by diseases affecting the vestibule or its afferent fibres
- Illusion of movement, dizziness, nausea

• Motion sickness -caused by mismatch between visual and vestibular information
- Improved if horizon visible

• "Bedspins" -caused by alcohol
- Ethanol infiltrates cupula, lowers density and causes it to "float", creating perception and movement

Question 13

What are the results of ototoxic drugs?

Answer 13

Over 600 medications are known to be harmful to hair cells and can result in temporary or permanent hearing loss and disorders of balance