Kinesthetic Sensing

The term kinesthesia refers to the perception of limb movement and position, and is often broadly defined to include the perception of force as well. These sensory perceptions originate primarily from the activity of mechanoreceptors in muscles, which provides the central nervous system with information about the static length of muscles, the rate at which muscle length changes, and the forces muscles generate. From these signals comes our awareness of where our limbs are in space, when our limbs have moved, and the mechanical properties of objects (e.g. weight, compliance) with which they interact. Sensory information about changes in limb position and movement also arises from other sources, namely receptors in the skin and joints. These inputs appear to be particularly important for kinesthesia in the hand, as both joint (Clark et al., 1989; Ferrell et al., 1987) and (or) cutaneous anesthesia (Clark et al., 1986) impairs the ability to detect finger movements and perceive finger positions. For more proximal joints, such as the knee, joint and (or) skin anesthesia does not have a significant influence on the perception of limb position (Clark et al., 1979). It appears that for the hand, cutaneous receptors provide an important facilitatory input to the central nervous system that is used to interpret position and movement signals arising from other sources. Cutaneous receptors in the hairy skin on the dorsum of the hand are capable, however, of encoding joint movement very precisely via their responses to stretch of the skin overlying the active joint (Collins & Prochazka, 1996; Edin, 1992). The importance of cutaneous sensory feedback to the perception of finger movements and positions is not surprising in view of the high innervation density of cutaneous mechanoreceptors in the hand, and its specialization for tactile exploration and manipulation. This feedback may also be more important for kinesthesia in the hand than for other parts of the body because of the complex anatomical arrangement of muscles, with most muscles acting over several finger joints, which would result in a considerable ambiguity of muscle spindle receptor discharges. In addition to these peripherally originating signals, there is evidence that central (cortical) feedback pathways provide information that is used to decode muscle afferent signals and in the perception of force.