Hearing + Ear (I) Flashcards
What is sound
A longitudinal pressure wave travelling through air or a medium
Which 2 characteristics make up sound
Frequency (pitch)
Amplitude (intensity/loudness)
How do you work out frequency
1/t
T = period between sounds
What would high frequency t be
Smaller intervals between sound
What would increase in pressure cause for intensity
Increased pressure increases intensity of sound
Does t change measuring intensity
No. Period of sound is same
How do you work out intensity of sound (decibels) from pressure (pa)
20 log (pa/20)
20 is a reference level
Why is 20pa pressure only 0 decibels
Intensity measured in log
Log 20 (20/20) = 0
Is frequency dependent on pressure
Not always, we can detect a high frequency even at lower pressures
at what frequency pitch does intensity need to be highest
At high and low frequencies
What makes up the outer ear
Pinna
Which part of ear allows detection of sound externally and also on all vertical plates (ie left right up down)
Pinna outer ear
Which part of ear conducts sound to middle ear from the pinna
Ear canal
What does the ear canal allow and why
Amplification / increase intensity of sound due to its resonance
Where does the outer ear terminate
Tympanic membrane
What allows equal pressure on either sides of tympanic membrane allowing sound / vibrations
Eustachian tube opening (not open in air flights = no pressure equilibrium)
What makes up the middle ear
Ossicles
Malleus , incus and stapes foot plate
Which part of the middle ear is the longest
Malleus
What are the inner ear ossicles for
Transfer of vibrations to the cochlea via the stapes foot plate
How is the stapes foot plate attached to the cochlea
Via the cochlea oval window
Middle ear allows sound waves to travel from air to liquid cochlea. What is this called
An impedance transformer
Why is there increased pressure at the stapes than at the tympanic membrane (overcoming gas to liquid)
Tympanic membrane has a larger area
But both stapes and TM have the same force applied (stapes lower area so more force in a smaller area = higher pressure )
Pressure = force / area
By how much is pressure increases in stapes
X 18
Why is the fact malleus is longer than incus a way to affect pressure and therefore gas liquid barrier
Acts as a lever
When force is applied to malleus this increases force of incus acting on stapes
What is the total increase in pressure in the middle ear due to lever and area
X25
Which cranial nerve is attached to cochlea
VIII
What are the 3 Scala filled with fluid in the cochlea
Scala tympani
Scala media (in middle)
Scala vestibuli
Which membrane separates Scala media from tympani
Basilar membrane
What fluid is present in the Scala tympani and vestibuli
Perilymph (high Na)
What fluid fills Scala media
Endolymph (high K)
Which membrane apart from basilar is between the Scala media and tympani
Tectorial
Which cells in the Scala media produce endolymph (k)
Stria vascularis
Which area does transduction or sounds to electrical signals happen
Organ of Corti (between the basilar membrane and tectorial) ie Scala media and tympani
Which fluid surrounds the apical (top) of the outer hair cells in organ of corti
Endolymph from the start of media
Which fluid surrounds the bottom of the outer hair cells
Perilymph from the Scala tympani
What is connected to hair cells in organ of corti
Nerve fibres
From stapes , where does sound vibrate down
From base to apex of the cochlea
What is pressed down due to pressure of the vibration sounds in the cochlea
The Scala media (basilar membrane being pressed down on)
If sound was at high frequency, where would maximal displacement be
At base (start of cochlea)
What frequency would it be if maximal displacement happened at apex of the cochlea(end)
Low freq
What does displacement of basilar membrane which therefore moves tectorial membrane cause
Hair cells to move
What are hairs on hair cells called
Stereocilia
What happens when inner hair cells stereocilia are excited
K moves in through the mechanically gated K channels (from endolymph)
Causes depolarisation of the cell (+ve charge)
Causes ca to enter and Nt vesicle fuse and release
Causes excitation of nerves
Why can K enter from the endolymph
The cell has a more negative membrane potential (-40) vs outside is 80+
When is K entrance into stereocilia regular amount
When hair cells are vertical
What happens if stereocilia bend towards the longest one
Links between the cilia stretch and cause more mechanically gated K channels to open
When is K entrance into cells stopped
Bending towards the shortest stereocilia blocks the mechanically gated K channels = no neurone excitation
How are outer hair cells response to sound different
They shorten and lengthen (not bend)
Which proteins allow shortening and lengthening of outer hair cells
Prestin
What does outer hair cell movements do
Causes even more displacement of the basilar membrane causing even more depolarisation at the inner hair cells
