Physiology of balance, taste, smell Flashcards Preview

202: Theme 2, Sensory inputs and motor outputs > Physiology of balance, taste, smell > Flashcards

Flashcards in Physiology of balance, taste, smell Deck (18)
1

Semi circular canals
- Structure
- Function

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

2

Orientation of semi-circular canals

Semi circular canals are orientated 90-degrees to one another

3

Otolith organs
- Structure
- Function

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

4

Mechanism of semicircular canals

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

5

Type I vestibular hair cells

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

6

Type II vestibular hair cells

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

7

Nystagmus
- Physiological
- Pathological

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]

8

Central vestibular pathwats

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]

9

Causes of vestibular disorders

Ear infections

Headinjury

Whiplash

ageing

Drugs:
- aminoglycoside antibiotcs

10

Mechanism of olfactory transduction

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-

11

Olfactory bulb targets

Areas where olfactory tract synapses

Pyriform cortex--> oribitofrontal cortex

Olfactory tubercle--> Thalamus, OFC, Hypothalamus

Amygdala--> Thalamus, OFC, Hypothalamus

Entorhinal cortex--> Hippocampus

12

Sweet taste transduction

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

13

Sour taste transduction

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

14

Bitter/Umami taste transduction

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

15

Salty taste transduction

Na+ moves into the receptor passively
- Uses Na+ equilibrium

16

Causes of taste disorders

Poor oral hygiene

Head injury

URTI

17

Central taste pathway
- primates

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

18

Central taste pathway
- Rodents

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