Lecture 18

Question 1

What are the main projection of the vestibular nuclei?

Answer 1

Extra-ocular muscles
Vestibulo-cerebellum
Spinal cord
Somatosensory cortex via the thalamus

Question 2

What are the functions of the semicircular canals?

Answer 2

Refers to canals, set up at right angles to each other and are able to detect movement in all three of the planes

Question 3

How do the ampullae transmit information to the vestibulo-cochlear nerve?

Answer 3

The ampullae contains a cupula within them that moves in response to the shifting endolymph that leads to the stereocilia moving.

Question 4

Describe how deflections of the stereocilia lead to action potentials being fired:

Answer 4

There will always be a tonic level of K+ entering into the cilia. When the cilia bend towards the longest cilia, the amount of K+ influx will increase, where they bend away the amount of K+ entering and hence action potentials being fired will decrease.

Question 5

Describe how the utricular macula are orientated:

Answer 5

Utricular macula are orientated horizontally

Question 6

How are the saccular macula orientated?

Answer 6

Saccular macula are orientated vertically

Question 7

Where does the receptors project to?

Answer 7

The receptors will communicate with the vestibular division of CNVIII, this then travels to the cell bodies within the vestibular ganglion, vestibular nuclei inn the medulla and a couple of second order axons will enter the cerebellum directly

Question 8

Where does the vestibular nuclei project to and briefly state what their functions are?

Answer 8

CN III, IV and VI nuclei (via MLF) – controls eye movements
Vestibulocerebellum- maintenance of static and dynamic posture
Spinal cord- coordination of head and neck movements – axial musculature and postural reflexes
Somatosensory cortex via thalamus- conscious perception of movement and spatial orientation (where signals are consciously perceived)

Question 9

What nerve innervated the dorsal oblique?

Answer 9

Trochlear nerve (IV)

Question 10

What nerve innervates the lateral rectus?

Answer 10

Abducens nerve

Question 11

Briefly describe the pathway that is involved in the vestibulo-ocular reflex:

Answer 11

• Excitatory connections to contralateral (meaning to the opposite side) CNVI nucleus and ipsilateral (meaning same side) CNIII nucleus
• Inhibitory connections to ipsilateral CN VI nucleus and contralateral CN III nucleus

Question 12

Describe Nystagmus briefly and mention the players that are involved:

Answer 12

• When eyes rotate slowly in one direction the eyes rotate slowly in the opposite direction (controlled by the vestibular nuclei)
• After a moment the eyes will quickly adjust to the new field of view- caused by the pontine gay centre

Question 13

Briefly describe the pathway and the function of the vestibulospinal reflex:

Answer 13

The axons of the lateral vestibulospinal nucleus extend down ipsilaterally over the whole spinal cord. This is referred to as the lateral vestibulospinal tract and mediates the vestibulospinal reflex. This gives us coordinated movement of the trunk as flexors will be activated on one side and extensors on the other.

Question 14

What are the general signs of vestibular disease?

Answer 14

1. Varying loss of equilibrium- imbalance and ataxia
2. Asymmetrical ataxia. Loss of balance but preservation of strength
3. Animal will probably have a loss of hearing and facial nerve deficits