Physiology of Balance, Taste and Smell

Question 1

Semi circular canals

-How many are there?

Answer 1

6 altogether(3 in each ear)

Detects rotation of the head
-L+R lateral, L anterior + R posterior, R anterior + L posterior functionally paired

• Canals connect to ampulla
• ampulla embedded in a cupula

Question 2

Otolith organs

-functional divisions

Answer 2

To detect tilt and acceleration

• the utricle- detects movement in the horizontal plane
• the saccule, which detects movement in the vertical plane.

Within the utricle and saccule, hair cells detect movement when crystals of calcium carbonate shift in response to it, leading to movement in the layers and displacement of hair cells.

Question 3

Mechanism of semicircular canals firing

Answer 3

Endolymph movement in the semi-central canals moves the axis of sensory hair cells

-This affects the frequency at which AP fire (CN8)

Question 4

Type I vestibular hair cells

-function

Answer 4

• Less common
• Surrounded by an afferent nerve calyx
• hair cells are not directly contacted by efferent nerve fibres
• signal/detect broad range of movements

Question 5

Type II vestibular hair cells

Answer 5

• Most common
• receive both afferent and efferent innervation
• more sensitive

Question 6

Nystagmus

• Physiological
• Pathological

Answer 6

Physiological-
slow eye movements followed by fast ones during continuous head rotation

Pathological- Spontaneous
Rapid side to side eye movements in the absence of head movements
-due to damage to semicircular canal (lack of firing)

Question 7

Causes of vestibular disorders

Answer 7

Ear infection
Head injury 
Whiplash
Ageing
Certain drugs, e.g. (gentamicin) –

Question 8

Olfactory tranduction

Answer 8

1. Odorant molecule binds to receptor cell
2. release of cAMP and opening channels
3. Na+ and Ca2+ influx-leads to AP
4. Opening of Cl- channels

Question 9

Hyposmia and anosmia

Answer 9

reduced ability or lack of smell and ability to detect odours

Question 10

Mechanisms of taste tranduction

-salt

Answer 10

purely passive

depends on the equilibrium potential for Na+ ions across the taste receptors

Question 11

Mechanisms of taste tranduction

-sour

Answer 11

H+ ions close K+ channels
via cAMP
leads to depolarisation

can be direct or indirect

Question 12

Mechanisms of taste tranduction

-sweet

Answer 12

cAMP as second messenger

closes K+ channels

Question 13

Mechanisms of taste tranduction

-bitter and umami

Answer 13

second-messenger induced increase in intracellular Ca2+ in the receptors. The Ca2+ increase leads to neurotransmitter release

Question 14

Causes of taste disorders

Answer 14

URTI

head injury

poor oral hygiene

Question 15

Central pathways of the gustatory system

Answer 15

Signals travels via CN 7, 9 and 10
Terminate on neurons on the solitary tract in medulla
travel to thalamus
gustatory cortex/orbitofrontal cortex

Question 16

What are the 2 distinct portions of the middle ear?

Answer 16

1. vestibular portion (semicircular canals for balance)

2. Auditory (cochlear)

Question 17

Describe the anatomy of the vestibular portion of the inner ear

Answer 17

3 semicircular canals
which are perpendicular to one another

each canal has a swelling at the end called the ampulla

there are 2 membranous sacs in the middle called the utricle and saccule