6.3 Summary of Sections 4 to 6

Hair cells do not have axons and therefore do not generate action potentials.

The nerve that communicates with or innervates the hair cells along the basilar membrane is known as the vestibulocochlear nerve or VIIIth cranial nerve. The cochlear portion of the nerve contains afferent fibres that carry information in the form of action potentials from the organ of Corti to the brain, and efferent fibres that bring information from the cerebral cortex to the periphery.

Most of the afferent fibres connect to inner hair cells with which they make a many-to-one connection. The nerve cells that innervate the hair cells at the apex of the cochlea are in the middle of the nerve bundle while fibres from the base of the cochlea make up the outside fibres of the nerve bundle. The frequency-to-place conversion seen in the cochlea is therefore preserved in the auditory nerve.

There are two main theories concerning the way in which the auditory system encodes the frequency of the signal: the frequency code and the place code. Evidence suggests that the frequency code operates for frequencies below 50 Hz whereas the place code operates at frequencies above 1000 Hz. Both appear to play a role for frequencies between these.

There are also two main theories regarding how the auditory system encodes intensity information: the firing rate of neurons and the number of neurons that fire.