Hearing

Question 1

Place code

Answer 1

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)

Question 2

Phase locking of APs

Answer 2

APs from a nerve discharge at a particular phase of the wave so give the brain an additional signal about location of sound waves

Question 3

Characteristic frequency

Answer 3

the most sensitive part of the bandpass filter at which the least energy is needed to get a response from the fibre

Question 4

Threshold

Answer 4

the amount of excitation needed to elicit an action potential i.e sound level needed at that frequency

Question 5

Interaural intensity differences

Answer 5

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

Question 6

Interaural time differences

Answer 6

(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

Question 7

Frequency

Answer 7

number of cycles per second; corresponds to pitch

Question 8

Phase

Answer 8

proportion of cycle through which the wave has advanced

Question 9

Wavelength

Answer 9

Speed of propagation/freq

Question 10

Amplitude

Answer 10

Amount of variation in pressure around the mean; corresponds to loudness

Question 11

Human hearing range

Answer 11

0-20000 Hz

Speech range is 3-5kHz so most sensitive here

Question 12

Function of pinna

Answer 12

Used for sound localisation in elevation

First spectral notch gives info

Question 13

Middle ear muscles

Answer 13

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

Question 14

Impendence matching

Answer 14

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

Question 15

Conductive hearing loss

Answer 15

middle-ear cavity filled with fluid and get low freq loss

Find greater sensitivity to conduction through bone when doing tuning fork test

Question 16

Sensorineural hearing loss

Answer 16

Damage to cochlea or auditory pathways

Question 17

Tonotopic map

Answer 17

Place code: frequency determined by the position of the hair cell signalling (due to being in position where basilar membrane is vibrating)

Question 18

Temporal coding of frequencies

Answer 18

Below 4kHz, can match the nerve discharge to the frequency detected (above a certain freq would take too many nerves to do this)

Question 19

Middle ear muscle reflex

Answer 19

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

Question 20

Lateral inhibition

Answer 20

OHCs counter vibrate against the sound at either end of specific position to inhibit adjacent parts firing so get more precise frequency range

Question 21

Central auditory pathway

Answer 21

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

Question 22

Basilar membrane basal end

Answer 22

Vibrates for higher frequency tones
Narrower and thicker

Form of vibration is a travelling wave?