Central responses to electrical activation of the peripheral nerves supplying the intrinsic hand muscles.

Abstract

In attempting to elicit low threshold monosynaptic reflexes from intrinsic hand muscles a different response was obtained. It occurred at a stimulus intensity above that for the alpha motor fiber threshold but at a latency similar to that expected from an H response. This was termed the "F" wave. A study of the identity of the motor units contained in the F response has shown them to arise from antidromic activation of a small number if motor neurons whose axons conduct the antidromic impulses. This response originates in the spinal cord and differs in terms of distribution, threshold, response to conditioning and lability from the monosynaptic reflex obtained from large postural muscles. In the normal state the response consists only of motor neurons contained in the direct motor response. In cases showing a loss of integrity of the upper motor neuron, a true reflex component appears superimposed on the antidromic response.