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Flashcards in Auditory System Deck (48)

What is sound ?

Audible variations in the air pressure


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 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 ?

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


What is the concentration of ions in the perilymph ?

Potassium ions - 7mM
Sodium ions - 140mM
This bathes the hair cells


How much more positive is the endolymph,oh compared to the perilymph ?

Endocochlear potential
This bathes the base of the hair cells


What happens when potassium channels on hair cells open ?

Potassium ions flow into the hair cells due to the high concentration of potassium ions in the endolymph


What are the potassium channels like in the stereocillia ?

They are mechanically gated channels
Elastic filaments link the lids of channels on different hair cells together - lids are only slightly open when the basilar membrane is still so there is only bey slight movement of potassium ions


What is the kinacillium ?

It is the largest stereocillia


What happens when the stereocillia move towards the kinacillium ?

Tips move away from each other and this causes the elastic filaments linking the lids to stretch and pull the lids open so more potassium ions can flow into the cells


What happens when the stereocillia move away from the kinacillium ?

The elastic filaments connecting the lids contract and the lids close completely


How many spiral ganglion cells does a single inner hair cells synapse onto ?

About 20
These cells control neurotransmitter release


What is the purpose of the outer hair cells ?

They amplify the movement of the basilar membrane
Contain motor proteins which can lengthen by contracting and this will further exaggerate the movement of the basilar membrane
Causing greater bending of the stereocillia so more chance of depolarisation and higher rate of AP firing


What happens in sensorineural hearing loss ?

It is hearing loss which occurs when cells dies meaning that signal transduction can no longer occur
Can be caused by congenital or environmental damage


What is the treatment for sensorineural hearing loss ?

Cochlear implant
Directly stimulates specific points on he basilar membrane to activate specific neurons in cranial nerve 8


How are frequencies below 200Hz encoded ?

By phase locking


Where is tonotopy seen for sound frequencies greater than 200Hz ?

Basilar membrane-spiral ganglion- cochlear nucleus


What is phase locking ?

It is the timing of neuronal firing
It complement the tonotopic map
It occurs with sound waves up to 4kHz because above this the sound wave cycles too fast for the action potentials of a single neuron to match the timings


When does neuronal firing= frequency ?

At low frequencies when the cell fires everytime the sound wave is in a particular phase


When does group firing rate= frequency ?

Where one cell does not Fire everytime but as part of a group so it is a combined effort - coverage


What is the ascending auditory pathway ?

Spiral ganglion
Ventral cochlear nucleus
Superior olive
Inferior colliculus
Medial geniculate nucleus of thalamus
Auditory cortex


Where does decussation occur in the ascending auditory pathway ?

2nd order neuron from the ventral cochlear nucleus decussates to the contralateral superior olive


What is the function of the inferior colliculus ?

Detection of sudden/strange/loud sounds - cause your head to turn


What are the 2 mechanisms for encoding sound localisation ?

Horizontal localisation - both ears
Vertical localisation - mono aural


What are the 2 mechanisms for horizOntal sound localisation ?

Interaural time difference
Inter aural intensity differenc e


What is interaural time difference ?

Time difference of sounds between both ears
- if the sound is closer to the left ear then It takes longer to hear it in the right ear
Sounds at a 45 degree angle causes a 0.3msec difference
Sounds at 90 degree able cause a 0.6msec difference


Where is the coincidence detector ?

Medial superior olive - contains lots of different neurons to help tell where sound is coming from
The neuron will only fire if it receive inputs from both ears


What is interaural intensity difference ?

Compares intensity of sound in each ear
Head causes sound to be muffled
Binaural inputs - excitatory inputs from AVCN and inhibitory inputs from MNTB to lateral superior olive