Cochlear function reflected in mammalian hair cell responses

Sensory receptor cells in the mammalian cochlea have fully differentiated into two distinct populations: inner and outer hair cells (IHCs and OHCs). This chapter describes the response patterns recorded in inner and outer hair cells in the apical three turns of the guinea pig cochlea. Characteristic frequencies (CF) in these regions are approximately 270 Hz in turn four, 1,000 Hz in turn three, and 4,000 Hz in turn two. Although these two receptors exhibit differences in resting membrane potentials and in response phase at low stimulus frequencies, they both produce ac and dc receptor potentials in response to sound. When measured around CF, both cell types produce a depolarizing dc response at low and moderate levels. At very low frequencies, IHCs are velocity detectors. Above several hundred Hertz, however, both IHCs and OHCs respond to basilar membrane displacement. All IHCs and OHCs recorded using the lateral approach in turns four, three, and two produce depolarizing responses when stimulated at and around CF.