Flashcards in 4.0 Auditory System Deck (51)
What is the range of frequencies that the ear can respond to?
20Hz - 20kHz
What is the intensity of sound measured in?
Decibels (usually expressed in log scale)
What is the formula for the amplitude of sound (decibels sound pressure level [dB SPL]) ?
dB SPL = 20log₁₀P/P₀
What is the minimal audible sound pressure detectable by normal human ears?
Define auditory threshold:
Sound pressure at which pure tone is just heard
Define pain threshold:
Sound pressure at which sound becomes painful
Structures of external ear:
Structures of middle ear:
1) Tympanic membrane
3) Middle ear cavity (temporal bone)
Structures of inner ear:
1) Vestibular apparatus (balance)
2) Cochlea (hearing)
Function of middle ear?
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
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)
At what sound levels do the muscles of the middle ear contract (reflex)?
How many dBs can the muscles of middle ear reduce sensitivity by?
30 - 40 dB SPL
What is the purpose of the eustachian tube?
Equalizes the pressure in the middle ear with atmosphere
Function of helicotrema?
Prevents partition from vibrating at subauditory frequencies. Only allows non damaging sounds
Define tonotropic map:
Different sound frequencies are mapped along the partition. This is not linear (logarithmic increments)
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
Where is the Organ of Corti?
On the basilar membrane along the whole length of the partition
What is the gelatinous mass covering the Organ of Corti?
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
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)
What secretes endolymph?
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
Inner vs Outer hair cells:
Presbycusis is the loss of hearing that gradually occurs in most individuals as they grow older
What are the afferent neurons of the cochlea?
(axons run in internal auditory meatus)
Where are the cell bodies of the bipolar cells?
Spiral ganglion (wraps around modiolus)
How much divergence occurs in auditory nerve fibres?
1 inner hair cell → 20 peripheral axons