2 SENSORY AND MOTOR SPECIALIZATION OF THE HAND

This chapter provides an overview of the basic properties of kinesthesia. Those properties, in conjunction with the tactile sensing capabilities described in chapter 1, delineate the features of the haptic sense. We will also consider the remarkable haptic sensing abilities of nonprimate species, such as rodents and moles, which use whiskers or fleshy appendages around their snouts to explore their environments tactually. The speed with which these animals are able to identify surfaces and prey, based on haptic cues, is truly extraordinary. In addition to receptors that respond to pressure and movement on the skin surface, there are sensors in the skin that detect changes in temperature. The properties of such cutaneous thermoreceptors are reviewed, together with their role in helping us to identify the material composition of objects in contact with the skin. Finally, the structure of the hand and associated musculature is described, along with the role of tactile signals in controlling hand movements.