ABSTRACT
Mechanical stimulation of a single hair results in the discharge of four or five sense cells thereby refuting the classical generalization that mononeural innervation is characteristic of the mechanoreceptive hairs.
By electrophysiological methods three functional units can be recognized: the ‘L’, ‘I’ and ‘S’ units. The ‘L’ unit conveys information about the duration and velocity of the dynamic phase; its discharge is phasic. The ‘I’ unit conveys information about the duration of the static phase and about the displacement of the hair; its discharge is tonic and the duration of discharge increases with extent of displacement. The ‘S’ unit is highly sensitive but responds only during the initial phase of displacement; if the hair is already extensively displaced the ‘S’ unit does not respond to further movement.
These findings indicate that all the functional units may be meaningfully concerned in encoding the parameters of a mechanical stimulus.
The widespread occurrence of multiple innervation of receptors, and its functional significance, is discussed; and a thorough re-investigation of stimulus—response relationships in the mechanoreceptive hairs of arthropods is advocated.
