Physiology of balance, taste, smell Flashcards

1
Q

Semi circular canals

  • Structure
  • Function
A

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

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2
Q

Orientation of semi-circular canals

A

Semi circular canals are orientated 90-degrees to one another

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3
Q

Otolith organs

  • Structure
  • Function
A

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

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4
Q

Mechanism of semicircular canals

A

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

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5
Q

Type I vestibular hair cells

A

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

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6
Q

Type II vestibular hair cells

A

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

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7
Q

Nystagmus

  • Physiological
  • Pathological
A

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]
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8
Q

Central vestibular pathwats

A

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]
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9
Q

Causes of vestibular disorders

A

Ear infections

Headinjury

Whiplash

ageing

Drugs:
- aminoglycoside antibiotcs

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10
Q

Mechanism of olfactory transduction

A
  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-
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11
Q

Olfactory bulb targets

A

Areas where olfactory tract synapses

Pyriform cortex–> oribitofrontal cortex

Olfactory tubercle–> Thalamus, OFC, Hypothalamus

Amygdala–> Thalamus, OFC, Hypothalamus

Entorhinal cortex–> Hippocampus

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12
Q

Sweet taste transduction

A
  1. Sweet molecule binds
  2. cAMP made
  3. Closes K+ channel –>Depolarisation
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13
Q

Sour taste transduction

A
  1. pH binds
  2. cAMP made
  3. Closes K+ channel –>Depolarisation
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14
Q

Bitter/Umami taste transduction

A
  1. Bitter/ umami molecule binds
  2. IP3 made–> Opens Ca2+ stores
  3. Increase in Ca2+ intracellularly–> release of NT
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15
Q

Salty taste transduction

A

Na+ moves into the receptor passively

- Uses Na+ equilibrium

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16
Q

Causes of taste disorders

A

Poor oral hygiene

Head injury

URTI

17
Q

Central taste pathway

- primates

A

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
Q

Central taste pathway

- Rodents

A

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