Final answer:
Frequency in the cochlea and auditory nerve is determined by the pitch of sound waves (which nerves fire) and the timing of nerve impulses (temporal theory of pitch perception). High frequencies activate hair cells at the cochlea's base, while low frequencies activate those at the apex. Above 1000 Hz, neural position rather than firing rate may provide frequency information.
Step-by-step explanation:
We can conclude that frequency is coded in the cochlea and auditory nerve based both on which nerves are firing (the pitch of the sound waves) and on the timing of nerve impulses in auditory nerve fibers (temporal theory of pitch perception). The pitch of the sound wave dictates which region of the basilar membrane within the cochlea vibrates, hence which hair cells are activated. This is the basis of the place theory. For example, high frequencies activate cells at the base of the cochlea, while low frequencies activate those at the apex. Regarding the timing of nerve impulses, the temporal theory suggests that the frequency of the sound is coded by the activity level of the sensory neurons. However, for frequencies above 1000 Hz, the nerve signals may instead indicate frequency by position along the cochlea rather than by the rate of nerve firing.