Vestibular Systems

Question 1

What is vestibular system

Answer 1

The Vestibular system is the sensory organ for detecting sensations of equilibrium
It is encased in the bony labyrinth and is continuous with the cochlea

Question 2

What are the functions of the vestibular system

Answer 2

Providing spatial reference for other sensory motor co-ordinations
Providing compensatory reflexes (Vestibular Ocular reflex)
Tuning cardiovascular function for re-orientations
Helping with perception of motion in space
Controlling balance reactions

Question 3

What are the parts of the vestibular apparatus

Answer 3

2 otolith organs and 3 semi-circular canals

Question 4

Describe the otolith organs

Answer 4

Utricle and saccule
Each has a sensory area called a macula
Detects linear acceleration and position of the head due to gravity

Question 5

Describe the semi-circular canals

Answer 5

Anterior, posterior and lateral 
Canals are filled with endolymph
Have swelling at the end called ampulla 
Arranged at right angles to each other
Detects angular acceleration

Question 6

Describe the macula

Answer 6

Small sensory area

Each has hair cells which synapse with the vestibular nerve

Question 7

Describe the hair cells of the maculae

Answer 7

Have minute projections called stereo cilia and a longer one called kinocilium
These project onto a gel layer with small calcium carbonate crystals - Otoconia

Question 8

Explain how the utricle and saccule function

Answer 8

1. Stereocilia and kinocilium project onto the otoconia
2. Gravity pulls on the otoconia or linear acceleration causes them to move
3. otoconia causes the stereocilia and kinocillium to move
4. Ion channels open and causes depolarisation or hyperpolarisation of the hair cells
5. Signals are sent to the vestibular nerve to give an idea of linear acceleration and the position of the head

Question 9

How do the semi-circular canals detect angular acceleration

Answer 9

When the head is moved one way, the SCCs move the same way
Endolymph moves in the opposite direction
This moves a structure in the ampulla called the cupola and stimulates hair cells and vestibular nerves

Question 10

Describe what happens in the semi-circular canals when the head is moved to the left

Answer 10

1. At least one of the SCCs on both sides of the head moves to the left
2. Endolymph in the SCC moves to the right
3. On the left, endolymph moves in a way that inhibits hair cells and decreases fibres
4. Increased firing of nerves on the right

Question 11

Define dizziness

Answer 11

a term used to describe a range of sensations, such as feeling faint, woozy, weak or unsteady

Question 12

Define vertigo

Answer 12

a feeling of spinning or whirling when you are not actually moving

Question 13

Define oscillopsia

Answer 13

a visual disturbance in which objects in the visual field appear to oscillate

Question 14

What are the differences between dizziness, vertigo and oscillopsia

Answer 14

Vertigo can cause dizziness
Vertigo occurs when stationary, while dizziness when stationary or moving
dizziness is more constant than vertigo oscillopsia

Question 15

Describe unilateral vestibular dysfunction

Answer 15

Dysfunction of one side
Unaffected side still generates tonic action potentials
Patients develop vertigo in opposite direction the lesion
Eyes passively drift towards the lesion, but beat back to the unaffected side (nystagmus)

Question 16

Describe bilateral vestibular dysfunction

Answer 16

Dysfunction of both vestibular systems
Decreased sensory input leads to dizziness as co-ordination and balance is affected
Vertigo is unusual (requires sensation of head turning but this doesn’t occur in bilateral dysfunction)