The vestibular system

Question 1

What is the vestibular system?

Answer 1

Provides information about balance and positioning

Question 2

What are the major anatomical structures of the vestibular system? (2)

Answer 2

• Semi-circular canals

- Otolith organs

Question 3

What is the function of the semi-circular canals?

Answer 3

3 different types detect different types of head rotation

Question 4

What are the ampullas and what is their function?

Answer 4

• Wide openings at the ends of the semi-circular canals

- Contain the hair cells (transducers)

Question 5

What are the 2 Otolith organs?

Answer 5

• Utricle

- Saccule

Question 6

What is the function of the Otolith organs?

Answer 6

Detect linear motion

Question 7

What kind of motion does the saccule detect?

Answer 7

Linear motion in the vertical plane (up and down)

Question 8

What kind of motion does the utricle detect?

Answer 8

Linear motion in the horizontal plane (backwards and forwards)

Question 9

How many semi-circular canals are there?

Answer 9

3

Question 10

How many Otolith organs are there?

Answer 10

2

Question 11

Which fluid is inside the semi-circular canals?

Answer 11

Endolymph

Question 12

What is the composition of endolymph?

Answer 12

High K+ content

Question 13

Which fluid is inside the Otolith organs?

Answer 13

Endolymph

Question 14

Which neurotransmitter is used in the vestibular system?

Answer 14

Glutamate

Question 15

How does the function of hair cells in the vestibular system differ from the auditory system?

Answer 15

Exactly the same function but vestibular hair cells respond to lower frequencies

Question 16

What range of frequency can the vestibular hair cells respond to?

Answer 16

0 - 20 Hz

Question 17

How does the structure of hair cells in the vestibular system differ from the auditory system?

Answer 17

• More rows of stereocilia in the hair bundle in the vestibular system
• Vestibular hair cells keep their kinocilium throughout their life but auditory hair cells don’t

Question 18

What is the kinocilium?

Answer 18

A special cilium which determines the polarity of the hair bundle

Question 19

What are the 2 types of vestibular hair cells?

Answer 19

• Type 1

- Type 2

Question 20

What is the difference between type 1 and type 2 vestibular hair cells?

Answer 20

• Type 2 has a normal synapse to afferent neuron

- Type 1 has expanded calyx afferent neuron

Question 21

What are macula?

Answer 21

Sensory patches containing hair cells inside the Otolith organs

Question 22

What lies on top of the hair cells in the Otolith organs?

Answer 22

Gelatinous otolithic membrane

Question 23

What are the otoconia?

Answer 23

Calcium carbonate crystals on top of the gelatinous otolithic membrane in the Otolith organs

Question 24

What is the striola?

Answer 24

• A line separating the hair cells in half in the Otolith organs
• The hair cells are positioned in opposite directions on either side so when one side is activated, the other is inhibited

Question 25

How is motion detected in the Otolith organs?

Answer 25

- Otoconia pull on the otolithic membrane due to gravity when there is movement - Hair bundles are in contact with the otolithic membrane which pulls the stereocilia towards the tallest/shortest one, causing depolarisation/hyperpolarisation - Half the hair cells are depolarised, half are hyperpolarised

Question 26

Which fluid is inside the ampulla?

Answer 26

Endolymph

Question 27

What is the cupula?

Answer 27

Gelatinous membrane in the ampulla into which hair cells project their hair bundles into

Question 28

How is motion detected in the ampulla?

Answer 28

- The higher inertia of the endolymph than the solid structures pushes the cupula during rotation - This pushes the cupula and the hair bundles in the opposite direction to motion

Question 29

How are the hair cells orientated in the ampulla?

Answer 29

In both ears, the hair cells are orientated with the tallest stereocilia towards the front (the face)

Question 30

How do the semi-circular canals work in pairs?

Answer 30

- The hair bundles are orientated in the same way which means that during motion, the hair cells in one ear are activated while the other ear is inhibited - The endolymph is moving in the same direction in both ears

Question 31

Which part of the brain is highly involved in motor coordination?

Answer 31

Cerebellum

Question 32

What is the vestibulo-ocular reflex?

Answer 32

Communication from the vestibular system to the visual system to keep the eyes stabilised during head movement

Question 33

What is vestibular nystagmus?

Answer 33

- Mechanism which enables the resetting of eye position during prolonged head rotation

Question 34

What are the phases of vestibular nystagmus?

Answer 34

- Slow phase where eyes rotate in the opposite direction to head movement - Quick phase where eyes are rapidly reset to the centre of the gaze