The auditory system Flashcards
What do we use sound for?
communication, emotion, recognising different sounds, 3D view of auditorial world, survival
What features of sound need encoding?
frequency, intensity, onset, duration
What are the 3 chambers of the cochlear spiral from top to bottom?
scala vestibuli
scala media
scala tympani
Where is the organ of corti and basilar membrane?
between the scala media and tympani
What parts of the cochlear spiral contain perilymph?
scala vestibuli and scala tympani
What are the contents of perilymph?
low K+, normal Ca2+ and high Na+ (same as extracellualr fluid)
What are the contents of endolymph compared to perilymph?
high K+, low Ca+ and low Na+
What is the purpose of the different ion concentrations in the cochlear chambers?
electrical driving force into hair cells is about 140mV overall which is vital for function
What is tonotopic organisation of the cochlea?
apex detects low frequencies and base detects high frequencies
sound wave travels from base to apex
How is the frequency of sound encoded?
the brain doesn’t receive sound- the position of the hair cell along the membrane that is depolairsed interprets how high or low it is
not coded by firing pattern, represented by location of cell only
What is the characteristic frequency location?
the location on the basilar membrane where there is maximal movement for a certain frequency
lower sounds will be closer to the apex, higher will be closer to the base
determined by width and stiffness of basilar membrane
High frequency sounds
short wavelength, low energy so don’t travel far and peak movement is at the base
Low frequency sounds
long wavelength, high energy so travels further and peak movement is at the apex
What is the role of inner hair cells?
primary sensory recpetors, encode all of the auditory info and pass it onto nerve fibres
What is the role of outer hair cells?
not sensory receptors, act as cochlear amplifiers by shortening and lengthening in time with sound frequency- electromotility
How do inner hair cells initiate action potentials?
mechanosensitive ion channels that are called MET channels are at the tips of the shorter stereocilia
connected to tip links that pull the channels open when sound waves move the IHCs
At rest when no sound is present:
slight tension in tip links
resting inward MET current
K+ enters down large electrical gradient
main driving force pushing K+ into cells
conc gradient for K+ exit is bigger than entry
hair bundle in endolymph, depolarised