Physiology of balance, taste, smell

Question 1

Semi circular canals

• Structure
• Function

Answer 1

6 altogether
- 3 in each ear

Detects rotation of the the head

• Lateral L+R are functionally paired
• Left anterior and Right posterior functionally paired [and opposite]

Canals connect to ampulla which contains cristae
- Ampulla connects to vestibular ganglion

Ampullae with sensory hair cells of semicentral canal
- Embedded in the capula

Question 2

Orientation of semi-circular canals

Answer 2

Semi circular canals are orientated 90-degrees to one another

Question 3

Otolith organs

• Structure
• Function

Answer 3

Saccule and utricle–> Inner ear

• Not exactly right angle to each other
• Sensory cells are embedded in gelatinous sheet with heavy crystals

Function
- Detects tilt and acceleration

Question 4

Mechanism of semicircular canals

Answer 4

Action potentials are always firing from the hair cells

Endolymph movement in the semi-central canals moves the axis of sensory hair cells
- This affects the frequency at which action potentials fire–> CN VIII

Question 5

Type I vestibular hair cells

Answer 5

Less common

• Receives both afferent and efferent fibres
• It is surrounded by the afferent nerve ending–> forming the calyx
• Only directly in contact with afferent fibres

Function
- Detects broad range of movements

Question 6

Type II vestibular hair cells

Answer 6

More common than Type I
- Directly in contact with the motor and afferent fibres

Function
- More sensitive to smaller range of movement than Type I hair cells

Question 7

Nystagmus

• Physiological
• Pathological

Answer 7

Physiological
- Slow then fast eye movements when the head rotates

Pathological–> Spontaneous

• Rapid side-to-side eye movements in the absence of head rotation
• Due to damage of a semi-circular canal [no firing]

Question 8

Central vestibular pathwats

Answer 8

Vestibular organs–> Cerebellum and vestibular nuclei

Vestibular nuclei–>

• Neocortex
• Reticular formation [input to CN3 nuclei]
• Oculomotor nuclei [input to extra ocular muscles]
• Spinal cord
• Cerebellum [also has input to vestibular nuclei]

Question 9

Causes of vestibular disorders

Answer 9

Ear infections

Headinjury

Whiplash

ageing

Drugs:
- aminoglycoside antibiotcs

Question 10

Mechanism of olfactory transduction

Answer 10

1. Odorant molecule binds to ciliated receptor cell
2. cAMP is produced in intracellular signalling–> Binds to non-selective cation channel
3. Influx of Na+ and Ca2+ into cell–> Depolarisation
4. Ca2+ binds to Cl- channels–> Efflux of Cl-

Question 11

Olfactory bulb targets

Answer 11

Areas where olfactory tract synapses

Pyriform cortex–> oribitofrontal cortex

Olfactory tubercle–> Thalamus, OFC, Hypothalamus

Amygdala–> Thalamus, OFC, Hypothalamus

Entorhinal cortex–> Hippocampus

Question 12

Sweet taste transduction

Answer 12

1. Sweet molecule binds
2. cAMP made
3. Closes K+ channel –>Depolarisation

Question 13

Sour taste transduction

Answer 13

1. pH binds
2. cAMP made
3. Closes K+ channel –>Depolarisation

Question 14

Bitter/Umami taste transduction

Answer 14

1. Bitter/ umami molecule binds
2. IP3 made–> Opens Ca2+ stores
3. Increase in Ca2+ intracellularly–> release of NT

Question 15

Salty taste transduction

Answer 15

Na+ moves into the receptor passively

- Uses Na+ equilibrium

Question 16

Causes of taste disorders

Answer 16

Poor oral hygiene

Head injury

URTI

Question 17

Central taste pathway

- primates

Answer 17

First order neurones

• CN 9
• Chorda tympani [CN 7]
• Lingual tonsilar nerve [CNX]
• Synapse with second order neurones at nucleus of solitary tract

Second order neurone
- Ascends and projects ipsilaterally into the ventral posterior nucleus of the thalamus

Third order

• Into insular cortex
• OFC

Question 18

Central taste pathway

- Rodents

Answer 18

First order neurones

• CN 9
• Chorda tympani [CN 7]
• Lingual tonsilar nerve [CNX]
• Synapse with second order neurones at nucleus of solitary tract

Second order

• Synapse at parabrachial nucleus
• Ventral posterior nucleus of the thalamus