The premotor potential.
A small waveform precedes the compound muscle action potential evoked from the thenar eminence with median nerve stimulation with high amplifier gains. This potential is believed to emanate from fibers destined to innervate the volar aspect of the first digit. It has been suggested recently that the source of the premotor potential is the palmar cutaneous branch of the median nerve. In this study, the palmar cutaneous branch of the median nerve was blocked at the wrist. A localized zone of anesthesia was observed over the proximal midpalm, not the thenar eminence, and the premotor response remained unchanged as did a midpalmar potential. The median nerve was then blocked at the base of the thenar eminence; only then did the premotor potential disappear. The palmar cutaneous branch of the median nerve innervates only a small portion of the medial aspect of the thenar eminence and does not produce the thenar premotor potential. Additionally, because of the close proximity of the main median nerve to its palmar cutaneous branch, volume conduction of stimuli and responses precludes an electrophysiologic technique which exclusively localizes the palmar cutaneous branch of the median nerve.
Dumitru
D
D
Department of PM&R, University of Texas Health Science Center, San Antonio 78284-7798.
Walsh
N E
NE
Ramamurthy
S
S
D000200:Action Potentials; D000328:Adult; D005385:Fingers / Q000294:innervation; D006225:Hand / Q000294:innervation*; D006801:Humans; D008475:Median Nerve / Q000502:physiology*; D009132:Muscles / Q000294:innervation*; D013933:Thumb / Q000294:innervation