Role of Single Mechanoreceptor Units in Tactile Sensation
A fundamental task of the hand is to extract information about surface structure, shape and weight of objects during manual exploration and manipulation. Much of this information is signalled from low-threshold mechanoreceptive units in the skin. Deep receptors of various types are also involved in the complex feedback mechanisms for motor control. We know from microneurographic studies in man that there are four basic types of low-threshold mechanoreceptive units in the glabrous skin of the hand. Extrapolation from animal experiments suggests that RA units are connected to Meissner corpuscles, PC units to Pacinian corpuscles, SA I units to Merkel disks, and SA II units to Ruffini end-organs (Lindblom and Lund, 1966; Iggo and Muir, 1969; Lynn, 1969; Chambers et al., 1972; Iggo and Ogawa, 1977). Detailed information is at present available about the stimulus-response functions, receptive field characteristics and innervation densities of these four unit types in the fingers and palm (Knibestöl and Vallbo, 1970; 1980; Knibestöl, 1973; 1975; Vallbo and Johansson, 1978; Johansson, 1978; Johansson and Vallbo, 1979; Johansson et al., 1982). Much less is known about the role of these mechano-receptive units in sensory experience. Here we describe a new technique for studying sensory correlates of single mechanore-ceptive unit activation and discuss the contribution of these units to tactile sensation and motor control.
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