[Electroneuromyographic study of the median nerve: peculiarities of M-response from the anterior forearm muscles during stimulation of the brachial plexus]

Abstract

Motor fibers of the median nerve innervating the anterior forearm muscles during stimulation of the brachial plexus have been studied. A role of forearm muscles innervated by the cubital and radial nerves in the formation of the M-response recorded from the anterior forearm muscles has been determined. Surface stimulating and recording electrodes have been used, with the active recording electrode being placed on the border between the upper and the middle one third of the anterior forearm surface and the reference electrode--in the area of the lower one third of the forearm. Nerve stimulation was conducted at 5 points: in the region of elbow flexion (median nerve); in the border between the middle and the lower one third of the inner side of the shoulder (median and cubital nerves); in the Erb's point or in the axillary space (brachial plexus); in the sulcus of ulnar nerve (cubital nerve); on the border between the middle and the lower one third of the outer shoulder surface (radial nerve). During stimulation of the brachial plexus, the M-response recorded from the anterior forearm muscles is caused mostly by the median nerve. The radial nerve also exerts a significant influence on development of the M-response. A role of the cubital nerve is minimal (p>0.05). The M-response recorded from the anterior forearm surface during brachial plexus stimulation is a result of summed potentials of motor units both of the anterior forearm muscles innervated by the median and cubital nerves and of the lateral and posterior groups innervated by the radial nerve.