Distal excitability properties of median motor axons

Excitability properties were recorded from 14 volunteers following stimulation of the recurrent motor branch of the median nerve in the palm. Distal stimulation resulted in significantly lower strength-duration time constant and lower threshold during prolonged hyperpolarization than did wrist stimulation in the same subjects. These differences may be geometric in origin or alternatively may arise from functional changes distally, particularly reduced expression of persistent Na(+) conductances and more hyperpolarization-activated current. Excitability studies using palm stimulation provide information closer to the neuromuscular junction, where membrane properties are preferentially affected in a variety of clinical conditions. (C) 2001 John Wiley & Sons, Inc.