The Mechanism of Myotonic Contraction

Abstract

The delayed relaxation of myotonic muscle is a result of the pathological state of the muscle itself, independent of the nervous innervation. In 2 human patients with Dystrophia myotonica, two shielded electrodes were placed on the median nerve and 2 needle electrodes punctured the proximal and distal part of the thenar eminence, respectively. The nerve was stimulated supramaximally with a thyratron stimulator and the source of the needle electrodes was an a-c potential reductor. Myographic registrations were made from the interphalangic joint of the first finger. A 2-sec. direct and indirect stimulation of 60 stimuli/sec. was given. Curare inj. into the brachial artery, with a venous tourniquet during 2 mins. after the injn., completely suppressed the effect of nerve stimulation. The direct stimulation, conversely, reproduced exactly the previous registration, showing that the myotonic delayed relaxation was not influenced by the synaptic exclusion. Also, the percussion of the muscles of the thenar eminence showed the same myotonic responses after full curarization.