Antidromic excitation of motoneurons by intramuscular electrical stimulation.

The terminal branches of motoneurons can be excited by electrical current pulses delivered via needles inserted intramuscularly. Observations are reported which indicate that tungsten semi-microelectrodes suitably positioned in a muscle belly can excite antidromically a large proportion of the alpha-motoneurons of that muscle, at stimulus strengths weak enough to avoid spread of excitation to motor units of adjacent muscles. Some gamma-motoneurons and afferent axons can also be excited by intramuscular stimulation. This technique of antidromic excitation will find application in electrophysiological studies on motoneurons of small muscles, such as intrinsic hand and foot musculature, where the individual muscle nerves are too fragile to be dissected and mounted on stimulating electrodes in the conventional manner.