The frequency selectivity of auditory nerve fibres and hair cells in the cochlea of the turtle

Abstract

SUMMARY1. The electrical responses of single auditory nerve fibres or cochlear hair cells were recorded in the isolated half-head of the turtle Pseudemys scripta elegant. Responses to sound stimuli presented to the tympanum could be recorded for at least 4 hr after isolation.2. Impulses were recorded extracellularly from single auditory nerve fibres. For tones of suprathreshold intensity the impulses occurred with a preferred phase relation (i.e. they were phase-locked) to the cycles of the sound stimulus. Nerve 3. Intracellular recordings were made from hair cells in the basilar papilla. Following injection of a fluorescent dye into a cell through the recording electrode, the dye was localized in a single hair cell in a transverse section of the cochlea.4. Hair cells had resting potentials of about -50 mV, and, to low frequency tones, gave periodic responses graded with the intensity and frequency of the stimulus. Recordings were obtained from cells with characteristic frequencies between 70 and 670 Hz.5. The voltage response to a pure tone at low sound pressure was sinusoidal for all frequencies of stimulation; at higher sound pressures a number of non-linearities were apparent in the response wave form. One of these was a steady depolarizing component, which, relative to the periodic component of the response, was most prominent at high frequencies.6. The amplitude of the response evoked in a hair cell by a low intensity tone was linearly related to the sound pressure; for loud sounds, the response eventually reached a saturating amplitude, which in some cells was as great as 30-45 mV peakto-peak.7. The linear sensitivity of a hair cell is defined as the r.m.s. voltage for a linear response of the cell at its c.f. divided by the sound pressure at the tympanum. In the most sensitive cells this value was 30-90 mV/Pa. 8. If the frequency selectivity of a hair cell was expressed in terms of the sound pressure needed to produce a constant amplitude of response, the sharpness of this frequency selectivity was found to be virtually independent of the response criterion for responses between 1 and 10 mV; in the cells which gave the largest responses, the

Activity patterns of cochlear ganglion neurones in the starling

“…Manley also reviewed the arguments against the possibility that preferred intervals arise through inadvertent noise stimulation of hair cells. Subsequently, similar phenomena have been reported in auditory nerve fibres of the red-eared turtle (Crawford and Fettiplace 1980) and the membrane noise of single hair cells of this turtle has been shown to preferentially contain energy in the region of the CF (Crawford and Fettiplace 1981 a, b). These data taken together not only strengthen the impression that spontaneous activity of auditorynerve fibres has its origin on the presynaptic side of the hair cell, they also indicate that the preferred intervals are a reflection of a frequency selectivity present in the unstimulated hair cell.…”

Essential Nonlinearities in Hearing

“…Individual hair cells show electrical frequency selectivity, being tuned to specific frequencies by resonance of the membrane potential [14]. A seven-dimensional conductance-based model describes the hair cell's electrical amplifier, called the membrane oscillator [15].…”

Specialization for underwater hearing by the tympanic middle ear of the turtle,Trachemys scripta elegans

“…In most turtle species, the ear is relatively insensitive. The auditory papilla is small but is organized tonotopically, such that higher frequency sounds excite the hair cells at the base, with the tones to which hair cells respond becoming lower towards the apex [12].…”