Graded Potentials and Spiking in Single Units of the Oval Organ, A Mechanoreceptor in the Lobster Ventilatory System

Open Access
Publisher Website
Google Scholar
Abstract
The peripheral dendritic arborizations of sensory units X, Y and Z of the oval organ have similar branching patterns. All three permeate the whole array of connective tissue strands without apparent regionalization or specialization. The analogue components of sensory responses elicited in fibres X, Y and Z when the connective tissue array is stretched show considerable diversity: fibre Z has a higher threshold than X and Y; the dynamic peak values of X and Y saturate at pulls mid-range for Z; X, Y and Z form a spectrum of increasing adaptation. Application of TTX abolishes impulse generation in fibre X earlier than in fibre Y, indicating diversity in spike initiating mechanisms from one fibre type to another. Fibre X only spikes between certain limits of membrane depolarization. Usually the response includes one to five spikes which occur during the dynamic phase of a trapezoidal stretch stimulus. Fibre Y fires throughout the stimulus duration for pulls of moderate amplitude and velocity. Spiking inactivation and a low maximum firing frequency (approximately 80 s−1) limit the range of length sensitivity in fibre Y. Fibre Z attains higher firing frequencies than either X or Y (approximately 110 s−1). The initial burst frequency (velocity dependent) may equal the firing rate of the dynamic peak.