The Vestibular System

Question 1

In general terms, where is the vestibular system located?

Answer 1

In the inner ear

Question 2

Name the specific sensory receptors involved.

Answer 2

Vestibular hair cells.

Question 3

What is the structure, location and stimuli detected by these sensory receptors?

Answer 3

Structure - Seperate cells
Location - proprioceptors
Stimuli - Mechanical and proprioceptive

Question 4

What is the function of the vestibular system?

Answer 4

The vestibular system gives you an awareness of balance and spatial orientation so that movements are coordinated and balanced e.g. through control of muscle tone - helps keep the head and trunk coordinated. It also helps controlling movements of the eyes

Question 5

What movements do the ampulla and semi-circular canal detect? What response does this cause?

Answer 5

These detect rotational movements as the semi-circular canal is arranged in 3 dimensions. Rotation causes displacement of the fluid in the ear, generating a force that moves the vestibular hair cells as it acts on the cupula. This causes local depolarisation and a graded potential which leads to an action potential. This travels along the 8th cranial nerve/ampullary nerve to the vestibular nuclei.

Question 6

What is the name of the nerve that carries information from the receptors to the vestibular nuclei?

Answer 6

8th cranial nerve via the scarpus ganglion.

Ampullary nerve

Question 7

What is the role of the cupula?

Answer 7

It is a extension that envelopes the vestibular hair cells, amplifying the movements of the hair cells and makes them more sensitive to movement so that balance is a finely tuned system.

Question 8

What movements do the saccule and utricle detect? What response does this cause?

Answer 8

They detect tilt e.g. skiing and acceleration/deceleration. e.g. in a car, lift. The movements act upon a structure called the otholithic organ which is affected by gravity. Gravity drags the hair cells down causing them to bend, this stimulates local depolarisation, a graded potential then an action potential which is transmitted to the vestibular nuclei via the 8th cranial nerve.

Question 9

What is the role of the otolothic organ?

Answer 9

Affected by gravity, causing the hair cells to be dragged down and bend = action potential.

Question 10

What is the function of the medial vestibulospinal tract?

Answer 10

Acts upon the postural muscles of the neck aiding with stability and balance through increasing muscle tone.

Question 11

What is the function of the lateral vestibulospinal tract?

Answer 11

Aids with movements of limbs to control posture and balance through muscle tone modulation.

Question 12

What are the inputs and outputs of the vestibular nuclei?

Answer 12

Inputs - Vestibular hair cells, vestibulocerebellum, basal ganglia.
Outputs - Vestibulocerebellum, medial and lateral vestibulotracts to target alpha and gamma motor neurones to target skeletal muscle fibres.

Question 13

Why does the vestibulocerebellum connect to the vestibular nuclei?

Answer 13

To help with the coordination of movement and muscle tone to aid with equilibrium, balance and posture

Question 14

Describe the vestibulo-occular reflex

Answer 14

Involuntary movements of the eyes in response to movements of the head when the eyes are fixed on a stable point.

Question 15

Describe the vestibulo-collic reflex

Answer 15

Acts on the neck postural muscles to correct orientation of the head and give stability in relation to the trunk.

Question 16

Describe the vestibulo-spinal reflex

Answer 16

Coordination of the head, neck and trunk to maintain/regain postural control through activation of the vestibulospinal pathways. e.g. if you’re pushed, you respond by spraying your arms out and increasing your base of support.

Question 17

What is the role of the vestibular reflexes?

Answer 17

To stabilise the head/neck, stabilise vision and upright posture.