Vestibular System

Question 2

Lecture 1

Answer 2

Physiology of Balance

Question 3

What are semicircular canals?

Answer 3

Organs of balance filled with inert endolymph similar to scala media.

Question 4

What are the semicircular canals of the vestibule?

Answer 4

Horizontal. Anterior. Posterior.

Question 5

Where do the canals meet?

Answer 5

Utricle.

Question 6

What do semicircular canals end in?

Answer 6

Ampulla.

Question 7

What is the ampulla?

Answer 7

Compartment containing the cupula, hair cells and endolymph.

Question 8

How is the ampulla innervated?

Answer 8

Afferent neurones going to the vestibular nerve.

Question 9

What is the function of the endolymph?

Answer 9

Pushes against cupula to cause depolarisations/hyperpolarisations.

Question 10

What activates the hair cells of the ampulla?

Answer 10

Head rotation.

Question 11

How do hair cells detect horizontal movement?

Answer 11

As well as the endolymph moving against the cupula, the otolithic membrane containing otoconia adds a gravitational pull on the hairs as the head rotates to detect linear acceleration.

Question 12

Describe the orientation of hair cells in semicircular canals.

Answer 12

All hairs in the same direction in each ampulla.

Question 13

Lecture 2

Answer 13

Central Processing in the Vestibular System

Question 14

What may cause vertigo and hearing loss?

Answer 14

Local blood supply deficit in the internal auditory and common cochlear arteries.

Question 15

What causes only vertigo?

Answer 15

Local blood supply deficit in the anterior vestibular artery.

Question 16

What is nystagmus?

Answer 16

Involuntary eye movement/jerking in one direction.

Question 17

What are the types of nystagmus?

Answer 17

Peripheral. Central. Spontaneous. Positional. Gaze-induced. Post-rotational.

Question 18

What causes peripheral nystagmus?

Answer 18

Normal or diseased functional states of the vestibular system.

Question 19

What causes central nystagmus?

Answer 19

Normal or abnormal processes not related to the vestibular system. Lesions of midbrain/cerebellum.

Question 20

What causes spontaneous nystagmus?

Answer 20

Random. Regardless of position of head.

Question 21

What causes positional nystagmus?

Answer 21

Specific position of head.

Question 22

What causes gaze-induced nystagmus?

Answer 22

Changing of gaze.

Question 23

What causes post-rotational nystagmus?

Answer 23

Rapid rotation/shaking of head.

Question 24

What causes Benign Paroxysmal Positional Vertigo (BPPV)?

Answer 24

Debris collected in the inner ear (otoconia/CaCO) shift when head moves causing false vertigo.

Question 25

What is AC-BPPV?

Answer 25

BPPV in the anterior semicircular canal. Causes down-beating positional nystagmus.

Question 26

What is LC-BPPV?

Answer 26

BPPV in the lateral/horizontal canal. Causes horizontal nystagmus.

Question 27

What is PC-BPPV?

Answer 27

BPPV in the posterior canal. Causes rotatory, up-beating nystagmus.

Question 28

How is PC-BPPV treated?

Answer 28

Epley maneuver.

Question 29

What is the vestibulo-ocular reflex?

Answer 29

Reflex eye movement caused by vestibular stimulation.

Question 30

What is the role of the vestibulo-ocular reflex?

Answer 30

Keeps retinal image stable, maintaining visual processing.

Question 31

Describe the direct mechanism of the vestibulo-ocular reflex.

Answer 31

Rotation of head bends hair cells in semicircular canals in the opposite direction. Hair cells depolarise and send signal to medial and lateral recti (muscles) of the eye via vestibular nuclei.

Question 32

Describe the indirect mechanism of the vestibulo-ocular reflex.

Answer 32

Head movement info travels to granule cells of cerebellum via mossy fibres. Parallel fibres of granule cells synapse onto Purkinje cells inhibiting vestibular nucleus. Climbing fibres send feedback from the eye muscles, inhibiting the vestibular nucleus.

Question 33

How is vestibular learning achieved?

Answer 33

Long term potentiation/depression at the parallel-purkinje synapses. Altered purkinje output via climbing fibre feedback.

Question 34

Describe the different distribution of cerebellar defects.

Answer 34

Cerebellar hemisphere syndrome - Affects half of body. Rostral vermis syndrome - Chest down (not hands). Caudal vermis syndrome - Affects chest to knees. Pan cerebellar syndrome - affets whole body.

Question 35

How is a lesion of one of the vestibular organs perceived by the brain?

Answer 35

As a head-turn in the opposite direction.

Question 36

What is the neurological term for the lesion of the vestibule?

Answer 36

Unilateral vestibular ganglionectomy.

Question 37

Describe the chemical mechanisms of vestibular compensation.

Answer 37

Downregulation of Glycine and GABA at ipsilesional vestibular nucleus causing smaller response to commissural inhibition of ipsilesional VN by contralesional VN. Upregulation of excitability of ipsilesional VN.

Question 38

Describe the physical mechanisms of vestibular compensation.

Answer 38

Cerebellar cortical plasticity reduces amount of inputs to contralesional VN. Reduces inhibition of ipsilesional VN by commissural fibres from contralesional VN.

Question 39

Describe the ganglionectomy experiments involving the dendrotoxin sensitive potassium current.

Answer 39

Compensated chicken embryos show small differences in response between lesioned and intact sides whereas embryos which have not undergone vestibular compensation show a significant difference in amplitude of the current.