ABNORMAL CONNECTIONS BETWEEN SKELETAL MUSCLE FIBERS

In two apparently healthy subjects EMG findings have been made of a type not previously encountered. The jitter between the muscle fiber action potentials from two different muscle fibers belonging to the same motor unit was only 2-3 μsec (S.D.), which is far less than that normally obtained (10-30 μsec). The jitter was unaffected by i.v. injection of 15 and 30 μg d-tubocurarine/kg body weight. Normally, a considerable increase of the jitter is seen at these doses. At the dose level 30 μg d-tubocurarine/kg, blocking of occasional discharges was seen, affecting both the fiber potentials simultaneously. Normally either one or the other of the two fiber potentials blocks in any one discharge. A hypothesis is presented whereby an abnormal connection existed between two or more fibers, so that activation of one fiber via its motor end-plate also activated the other fiber. © 1969.