Functional properties of peripheral sensory units in hairy skin of a cat's forelimb

The properties of peripheral cutaneous units in the hairy skin of cat's forelimb were studied by single-fiber recordings with tungsten microelectrodes. The response properties and receptive field (RFs) of total 193 units in superficial branch of radial nerve (SRN) were studied. The SRN sample included the following five major types of mechanoreceptive units; two types of low-threshold units (type I and II, slowly adapting), two types of hair units (G and D, rapidly adapting) and field units (F, responding principally to slow skin movement). Afferent conduction velocities of these units ranged from 9.0 to 56.0 m/sec. D hair fibers conducted much slower than other types of afferents and their conduction velocities were between 9.0 and 23.3 m/sec. Most of the smaller RFs of G, D and F units were found in the paw and digits. The disto-proximal increase of the mean size of RFs was marked in D hair units. The distributions of the RFs of simultaneously recorded paired units, which were supposed to be adjacent fibers, were examined. Among 23 paired units, more than half of them were homonymous combinations of unit types and there were no marked prevalence of particular types in heteronymous combinations. The RFs of paired units were close to each other, but showed little overlaps and some were separated by up to several cm over the skin surface. Some functional properties of cutaneous afferents from the forelimb were discussed.