Distal excitability properties of median motor axons

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