THE STRUCTURE AND FUNCTION OF THE SLOWLY ADAPTING TYPE II MECHANORECEPTOR IN HAIRY SKIN

Abstract

The slowly adapting type II mechanoreceptor in hairy skin of the cat was studied in detail using histological and neurophysiological methods. The end organ (Ruffini ending) was lightly encapsulated, situated in the dermis and supplied by one axon which bifurcated within the capsule to form a terminal arborisation. A serial diagrammatic reconstruction was made of one ending. The afferent units almost invariably carried a resting discharge and responded to vertical displacement of the skin over an area of 2·5 sq. cm and to directional stretching of the skin over an area up to 25 sq. cm. For each unit there was a single small region of maximum sensitivity (less than 2 sq. mm). The response to vertical displacement consisted of a dynamic and static phase, linked by a period of adaptation. These three phases were subjected to quantitative tests, using displacements of different amplitude, velocity and duration. The units were directionally sensitive to skin stretch and this response was of a similar pattern to that caused by vertical displacement. The units were temperature sensitive over a range from 14°–42°C and the resting discharge was increased by a fall in skin temperature and temporarily silenced by an increase.