We are all aware of where our limbs are and what they are doing, whether moving or still, and whether exerting effort or not. The origin of this muscle sense, or kinesthesis, has been debated for well over a century but, rather surprisingly, certain essentials remain unresolved. The central question is where the neural signals come from to impinge upon the sensorium (or higher sensory centers) and so lead to our conscious sensation. The ensuing question, one currently much less accessible to investigation, is how the information from different sources is compounded to produce the overall sensory experience. The obvious source for the underlying sensory input is the discharge of specific afferent receptors in muscle, tendon, joint, and skin. As long agreed, there can be no doubt that at least some of these play an essential role. It is less intuitively apparent, however, that in principle muscle sense could equally derive from the activity of the motor centers by their supplying the sensory centers with copies of the appropriate outgoing motor messages (corollary discharges). This may be illustrated by a conceptually simple, but largely disproved, example.
KeywordsMuscle Spindle Joint Position Sensory Experience Motor Center Muscle Afferents
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