4.0 Auditory System Flashcards Preview

MedST IB: Neurobiology and Human Behaviour (NHB) > 4.0 Auditory System > Flashcards

Flashcards in 4.0 Auditory System Deck (51)
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1

What is the range of frequencies that the ear can respond to?

20Hz - 20kHz

2

What is the intensity of sound measured in?

Decibels (usually expressed in log scale)

3

What is the formula for the amplitude of sound (decibels sound pressure level [dB SPL]) ?

dB SPL = 20log₁₀P/P₀

4

What is the minimal audible sound pressure detectable by normal human ears?

20μPa

5

Define auditory threshold:

Sound pressure at which pure tone is just heard

6

Define pain threshold:

Sound pressure at which sound becomes painful

7

Structures of external ear:

1) Pinna
2) EAM

8

Structures of middle ear:

1) Tympanic membrane
2) Ossicles
3) Middle ear cavity (temporal bone)

9

Structures of inner ear:

1) Vestibular apparatus (balance)
2) Cochlea (hearing)

10

Function of middle ear?

Electrical transformer

11

How does middle ear match the low impedence in air to the high impedence in cochlear fluid?

1) Area of eardrum = 14x times the area of footplate of stapes, therefore the pressure at stapes is 14x the eardrum
2) Ossicular chain acts a lever

12

What are the muscles of the middle ear?
What is their function?

1) Tensor tympani (attatches to malleus)
2) Stapedius (alters angle of stapes at oval window)

These two muscles reduce sound transmission (thus offer protection)

13

At what sound levels do the muscles of the middle ear contract (reflex)?

80dB SPL

14

How many dBs can the muscles of middle ear reduce sensitivity by?

30 - 40 dB SPL

15

What is the purpose of the eustachian tube?

Equalizes the pressure in the middle ear with atmosphere

16

Function of helicotrema?

Prevents partition from vibrating at subauditory frequencies. Only allows non damaging sounds

17

Define tonotropic map:

Different sound frequencies are mapped along the partition. This is not linear (logarithmic increments)

18

What is the travelling wave:

Caused by vibration of the partition. The partition executes a travelling wave that moves from base to apex. Each point undergoes a sinusoidal vibration with the amplitude being highest at its characteristic place on the tonotropic map.

Phase lag (where more apical points lag behind stapedial ones) = proof that this is not a standing wave

19

Where is the Organ of Corti?

On the basilar membrane along the whole length of the partition

20

What is the gelatinous mass covering the Organ of Corti?

Tectorial membrane

21

How many rows do outer hair cells have?
How many rows do inner hair cells have?

outer hair cells = 3 longitudinal rows
inner hair cells = 1

22

What is the type of fluid in the following?

1) Scala vestibuli
2) Scala tympani
3) Scale media

1) Scala vestibuli = perilymph
2) Scala tympani = perilymph
3) Scale media = Endolymph (more potassium + 100mV more positive)

23

What secretes endolymph?

Stria vascularis

24

How does mechano-electrical transduction occur in the streriocilia?

Steriocilia = microvilli

Movements of steriocilia are linked to opening and closing of cation channels

Movement towards longest steriocilia = opening
Movement towards shortest = closing

25

Inner vs Outer hair cells:

"
"

26

Define presbycusis

Presbycusis is the loss of hearing that gradually occurs in most individuals as they grow older

27

What are the afferent neurons of the cochlea?

Bipolar cells

(axons run in internal auditory meatus)

28

Where are the cell bodies of the bipolar cells?

Spiral ganglion (wraps around modiolus)

29

How much divergence occurs in auditory nerve fibres?

Lots
1 inner hair cell → 20 peripheral axons

30

How is intensity coded in auditory nerve fibres?

↑ sound pressure → ↑ firing rate

This saturates at 40dB > fibre threshold
(because fibres have different thresholds, overall range of intensities is 80dB)