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Physiology 2: neuro > Auditory and Vestibular > Flashcards

Auditory and Vestibular Flashcards

1
Q

Hair cell

A

A cell generally composed of stereocilia, a cell body and a synapse (onto an afferent nerve fibre).

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2
Q

Stereocilia

A

Are rigid, non-motile, actin filled rods, or “hairs”.

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3
Q

Afferent nerve

A

The nerve cell stimulated, via a synapse, by hair cells. This is the 8th cranial nerve in the case of auditory and vestibular hair cells.

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4
Q

Endolymph

A

A potassium-rich extracellular fluid is critical to the function of hair cells.

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5
Q

Basilar membrane

A

The membrane which houses auditory hair cells. The basilar membrane selectively vibrates to different frequencies at different points along its length, this underlies perceptual frequency selectivity.

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6
Q

Tip links

A

Found at the top of the cilia

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7
Q

Connectors

A

Lateral-link, top connectors, shaft connectors and ankle links.

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8
Q

Stereocilia bundles: TIP links

A
  • Tension in the ‘Tip-links’ distorts the tip of the stereocilia mechanically
  • This distortion allows channels to open and close with cilia movement. Current flows in proportionately.
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9
Q

Stereocilia bundles: Lateral link connectors

A

teral-link connectors between the shafts of stereocilia hold
the bundle together to allow it to move as a unit

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10
Q

Hair cells

A
  • Tip-links’ open ion-channels.
  • Endolymph high in K+.
  • Potassium ion (K+) influx depolarises the cell.
  • Voltage gated Ca2+ channels open.
  • Ca2+ triggers neurotransmitter release at the synapse.
  • Post-synaptic potential in nerve fibre triggers an action potential.
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11
Q

Inner ear is formed of:

A
  • Semicircular canals (vestibular system)

* Cochlea (auditory system)

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12
Q

Semicircular canals: sensing rotation

A
  • Rotation causes fluid motion in the semicircular canals.
  • Hair cells at different canals entrances register different directions

Roll: rotation around X-axis - Posterior semicircular canal
Pitch : Anterior semicircular canal
Yaw: Rotation around Z-axis

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13
Q

Hair cells for sensing rotation

A
  • Cilia are connected to the gelatinous cupula.
  • Under the motion, fluid in the canals lags to due to inertia, pulling the cupula in the opposite direction to the rotation of the head.
  • Cilia are displaced, depolarising hair cells.
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14
Q

Orientation and motation in mammals

A
  • In the otolith organs they are sensitive to linear acceleration.
  • Gravity is also acceleration.
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15
Q

How the otolith organs

A
  • Hair cells are topped by a rigid layer of otoconia crystals.
  • Under acceleration the crystal layer is displaced, deflecting the cilia.
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16
Q

Hair cells as water motion detectors: The lateral line system

A
  • Most fish and amphibians have a lateral line system along both sides of their body.
  • Mechanoreceptors provides information about movement through water or the direction and velocity of water flow.
  • Important for schooling.
  • Some mechanoreceptors, or neuromasts are in canals.
  • Superficial neuromasts are on the surface.
  • Neuromasts function similarly to the mammalian inner ear.
  • A gelatinous cupula encases the hair cell bundle and moves in response to water motion.
  • Most amphibians are born (i.e. tadpoles) with lateral lines.
  • Some (e.g. salamander) lose them in adulthood.
  • More aquatic living species retain them.
17
Q

Auditory system

A 
Cochlear nucleus 
Olivary complex 
Lateral lemniscus
Inferior colliculus 
Medial geniculate body 
Auditory cortex
18
Q

Sound: Rapid variation of air pressure

A

• Longitudinal pressure waves in the atmosphere.

19
Q

Frequency and wavelength

A

λ = c/f
c = speed of sound (344m/s)
f = frequency
λ = wavelength

20
Q

Sound level

A
  • The difference in amplitudes between the quietest sounds we can hear is massive
  • Normal air pressure: 100k Pascals.
  • We can hear a .000000001% change in pressure.
21
Q

Sound pressure level

A 
The decibel scale:
a “log” of ratio relative to 20Pa:
 20log 10(amplitude/20)
20Pa 	0dB SPL
200Pa 	20dB SPL
2000 Pa	40dB SPL
22
Q

The pinna

A
  • Size and shape varies from person to person.
  • Gathers sound from the environment and funnels it to the eardrum.
  • Made entirely of cartilage and covered with skin.
23
Q

Filtering by the pinna

A

The outer ear filters, influencing the frequency response.

Pinna features influence the entering sound differently

24
Q

Grade 1 microtia

A

A less than complete development of the external ear with identifiable structures and a small but present external ear canal

25
Q

Grade 2 microtia

A

A partially developed ear (usually the top portion is underdeveloped) with a closed stenotic external ear canal producing a conductive hearing loss.

26
Q

Grade 3 microtia

A

Absence of the external ear with a small peanut-like vestige structure and an absence of the external ear canal and ear drum. Grade III microtia is the most common form of microtia

27
Q

Grade 4 microtia

A

Absence of the total ear or anotia

28
Q

The tympanic membrane

A

The ‘ear-drum’ vibrates in response to sound.

Middle ear bones (ossicles) are visible through the membrane.

29
Q

The ossicles

A

Smallest bones in the human body.

Connects the tympanic membrane to the oval window of the cochlea.

30
Q

Glue ear (otitus media/OM)

A

Middle ear fills with fluid which impedes motion of the ossicles.
Reduces middle ear gain, raises hearing thresholds.
Very common in small children (<5 yrs) - can lead to development problems.

31
Q

The cochlea and basilar membrane

A

The cochlea: fluid filled spiral canal divided by a flexible membrane.
Basilar membrane filters sound according to frequency.

32
Q

The organ of Corti

A

The organ of Corti sits on top of the basilar membrane, within the scala media.
Inner and outer hair cells are mounted on it.

33
Q

The organ of Corti in action

A

The motion of the organ of Corti on the basilar membrane causes displacement of the stereocilia.
Outer hair cells contact the tectorial membrane. Inner hair cells do not.

34
Q

Outer hair cell: ‘rock and roll’ hair cell

A

Outer hair cells are motile.

Influx of positive ions makes the outer hair cells contract

35
Q

The cochlear amplifier

A

• Prestin in short conformation state
• Outer hair cell contracts
• This pulls the basilar
membrane toward the tectorial membrane.
Amplifies by as much as 50dB!!
Quiet sounds are amplified.
Loud sounds are not amplified – helps us deal with 120dB of dynamic range.
Tuning is sharper than the passive vibration of the basilar membrane.

36
Q

The ‘battery’ driving cochlear hair cell

A
  • The high potassium concentration of the endolymph of the scala media creates a 2x amplification.
  • If it were not potassium rich then inner hair cell output (of the cochlea nerve) would be halved, making sound perceptually quieter.
  • And the cochlea amplification would be much smaller, again making sounds perceptually quieter.

Physiology 2: neuro (19 decks)

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