Through The Auditory System

Question 0

What does the motion of the stereocilia of the inner hair cells produce?

Answer 0

It produces an electrical change in the cell (depolarisation) leading to the release of a chemical neurotransmitter that induces electrical impulses (spikes) in adjacent auditory nerve fibres.

Question 1

What does the vibration of the basilar membrane cause?

Answer 1

The vibration of the basilar membrane causes a shearing force between the basilar membrane and the overlying tectorial membrane.
In turn this causes the stereo-cilia on the tops of the hair cells to sway at the same rate as the basilar membrane.

Question 2

What happens to neural firing rates as the sound level increases?

Answer 2

Neural firing rates increase as sound level increases; until they saturate at a firing rate of about 200 spikes per second.
High spontaneous rate fibres start to increase their firing at low sound levels (they have low thresholds) but they also saturate at fairly low levels - up to 60db.
Low spontaneous rate fibres have higher thresholds and much higher saturation levels (e.g. 100db)

Question 3

What is phase locking?

Answer 3

Because inner hair cells depolarize when their stereo cilia are bent in one direction (away from the centre of the cochlea). Nerve fibres tend to fire a particular phase of the basilar membrane vibration for frequencies up to about 5000hz. This is called phase locking.

Question 4

How is information about a sound represented in the auditory nerve?

Answer 4

Either in terms of firing rate (nerve fibres represent the magnitude of vibration at different places on the basilar membrane.
And in terms of phase locking or firing synchrony
(Nerve fibres represent the temporal pattern of vibration at different places on the basilar membrane)