Hearing Flashcards
Place code
the frequency detected by a auditory fibre via an inner hair cell depends on the location at which the basilar membrane is made to vibrate by that specific frequency (and at which the hair cell is located)
Phase locking of APs
APs from a nerve discharge at a particular phase of the wave so give the brain an additional signal about location of sound waves
Characteristic frequency
the most sensitive part of the bandpass filter at which the least energy is needed to get a response from the fibre
Threshold
the amount of excitation needed to elicit an action potential i.e sound level needed at that frequency
Interaural intensity differences
for high freq sounds, the head shadows the sound source so other eat gets less intense sound
So if the sound is less intense on contralateral side, get more output from LSO
Interaural time differences
(better for low freq) sound must travel further to get to one ear than the other (except for 0degrees azimuth); interaural time delay
MSO gets input from both ears; axonal path to neurons increases gradually to different neurons but in opposite directions for the ears
Impulse from the closer ear to sound can travel further than other
Place of neuron in the MSO that fires due to signal from both ears reaching it at same time, signals the ITD
Frequency
number of cycles per second; corresponds to pitch
Phase
proportion of cycle through which the wave has advanced
Wavelength
Speed of propagation/freq
Amplitude
Amount of variation in pressure around the mean; corresponds to loudness
Human hearing range
0-20000 Hz
Speech range is 3-5kHz so most sensitive here
Function of pinna
Used for sound localisation in elevation
First spectral notch gives info
Middle ear muscles
Tensor tympani and stapedius: act to dampen vibration of ossicles
Contract before vocalisation to protect ears from own voice
Attenuates low freq more than high to acts to increase sensitivity to high freq sounds
Impendence matching
Oval window is 14X smaller
Lever ratio of the ossicles gives 1.2X increase
Overal get 18X increase in pressure passed on to correspond to 18X increases resistivity of fluid in cochlea
Conductive hearing loss
middle-ear cavity filled with fluid and get low freq loss
Find greater sensitivity to conduction through bone when doing tuning fork test
Sensorineural hearing loss
Damage to cochlea or auditory pathways
Tonotopic map
Place code: frequency determined by the position of the hair cell signalling (due to being in position where basilar membrane is vibrating)
Temporal coding of frequencies
Below 4kHz, can match the nerve discharge to the frequency detected (above a certain freq would take too many nerves to do this)
Middle ear muscle reflex
Cochlea via CNVIII (vestibulocochlear nerve) to ventral cochlear nucleus to superior olivary complex (both sides) to facial nerve nucleus -> via facial nerve to stapedius
Get contraction of both stapedius muscles in response to loud sound
Lateral inhibition
OHCs counter vibrate against the sound at either end of specific position to inhibit adjacent parts firing so get more precise frequency range
Central auditory pathway
Auditory nerve from cochlea, cell body in spiral ganglion to terminate in cochlear nucleus; layers DCN, PVCN and AVCN
Then goes SOC nuclei for sound localisation, + olivary nuclei
In midbrain reaches central nucleus of inferior colliculus where unconscious auditory map is
- Goes to mediate geniculus and to A1 auditory cortex
Basilar membrane basal end
Vibrates for higher frequency tones
Narrower and thicker
Form of vibration is a travelling wave?
