Which of the following physiologic responses occurs as the pitch of a sound is increased?
The primary change in the cochlea that registers an increase in the frequency of a sound wave is a change in the position of maximal displacement of the basilar membrane. A sound of low pitch produces the greatest displacement toward the apex of the cochlea and produces the greatest activation of hair cells at that location. As the pitch is increased, the position of greatest displacement moves closer to the base of the cochlea. Increases in the number of hair cells that are activated and in the frequency of discharge of units in the auditory nerve fibers, together with an increase in range of frequencies to which such units respond, are all more likely to be observed in response to increases in the intensity of a sound stimulus rather than to increases in pitch. In the auditory coex, sound frequencies are organized topographically so that a change in pitch may be represented by a change in the location of activated coical units. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 10. Hearing & Equilibrium. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e
The frequency of action potentials in auditory nerve fibers increases
Units in the auditory nerve become responsive to a wider range of sound frequencies
A greater number of hair cells become activated
The location of maximal basilar membrane displacement moves toward the base of the cochlea