Auditory System Flashcards
What does intensity of sound refer to ?
Amplitude of the wave
It is the difference in pressure between compressed and rarefied patches of air in a sound wave
It determines loudness
What is sound ?
Audible variations in the air pressure
What does the frequency of sound refer to ?
Number of waves per second
Expressed as Hz
It determines pitch
What does the middle ear do ?
It converts the wave in air to a wave in fluid
What are the ossicles of the Middle ear ?
They are within air filled cavities
They provide amplification of the sound - they amplify the signal from the tympanic membrane to cause the fluid in the cochlear to move
- malleus, incus and stapes
What is the attenuation reflex ?
It dampens the sound when it is very loud
The stapedius and tensor tympani muscles contract to reduce the movements of the ossicles so the fluid ,movement doesn’t damage the hair cells in the cochlear
What is conductive hearing loss ?
Scar tissue due to an infection or otosclerosis( proliferation of bone) causes decreased movement of ossicles
What is a major part of the outer ear ?
Pinna
Made up of elastic cartilage which funnels the sound wave down the auditory canal so it hits the tympanic membrane
What is the inner ear like ?
It is a snail shaped fluid filled cavity sitting in the skull
3 channels- scala vestibuli, media and tympani
Contains the basilar membrane which is floppy and moves up and down due to fluid flow
How does the basilar membrane move ?
Pressure changes cause the oval window to move
Moves the perilymph in the scala vestibuli
This moves the reissners membrane which moves the endolymph
This causes the basilar membrane to move creating a travelling wave
How are different frequency sounds heard ?
Different frequency sounds cause movement of the basilar membrane at a specific part
This determines which hair cells move
What is the organ of corti ?
It is on top of the basilar membrane and contains hair cells and auditory receptor neurons
The hair cells extend and implant into the rigid tectorial membrane
What does the round windows do ?
Allows the cochlear to bulge out a little to reduce the pressure
What is the helicotrema ?
It connects the scala vestibuli and tympani and allows fluid to flow from one side to the other causing the membrane to move
Where are high frequency sounds heard on the basilar membrane ?
They are able to vibrate the stiff base but they don’t travel far
Where are low frequency sounds heard on the basilar membrane ?
There energy doesn’t dissipate so they can travel further but they don’t have enough energy to vibrate the stiff base
What is the purpose of the tonotopoc organisation of the basilar membrane?
It’s called frequency coding
Enables the brain to know which part of the basilar membrane has moved and therefore which hair cells have moved enabling it to determine the frequency of the sound
Works to about 200Hz
What happens is the main purpose of the auditory receptors (hair cells) ?
They are the point where mechanical energy is changed into membrane potential
What are the types of hair cells ?
Inner and outer hair cells
3x more outer hair cells but it is the inner hair cells which pass on most of the information about movement of the membrane
What structures are linked to the basilar membrane to form a structural unit ?
Basilar membrane
Reticular laminar
Rods of corti
Hair cells
What happens when the basilar membrane moves downwards ?
Reticular laminar also moves downwards and away from the modiolus
This causes the stereocillia to bend in
What happens when the basilar membrane moves upward ?
Reticular laminar moves upwards and in towards the modiolus
This causes stereocillia to bend out
What makes the hair cells rigid ?
The actin in the filaments
What are the concentration of ions in the endolymph ?
Potassium ions - 150mM
Sodium ions - 1mM
