The philosopher's statement, now more than a century old, that there is nothing in the mind that has not come in through the senses, might be applied to motion in general. Certainly, so far as those movements due to the central nervous system are concerned, we may say that there are extremely few motions that have not had their antecedent afferent impulses. The modern conception of the nervous system regards it as a mechanism in which afferent impulses, arising in the various kinds of peripheral receptors or sensory endings are gathered up into a definite body of sensory impulses, and somewhere in their course, are summed or integrated to a definite orderly motor response.
For example, when a child is learning to write, and is copying a simple figure, afferent impulses are passing in from various peripheral sources, not from the eye alone, but also from the skin,