Electro-myographic investigation on the human external sphincter muscle of anus.

Abstract

Using the needle electrode, the human external sphincter muscle of the anus was studied and fhe following results were obtained.A. The muscle as a whole1. Interference voltages appear with a slight increase of constriction of the muscle-a property common to the circular muscles of the mouth and eye.2. The discharge can be abolished with difficulty by a distention of the anus provoked by an intentional motive; in an electrically silent state thus caused, an interruption of the effort results in an immediate return of the discharges in many NMU.3. Disappearance of the discharge can be brought about with comparative ease when the rectum is full with feces or other artificial substitute.4. Reflex changes of the discharge may be produced by such different causes, like the change in abdominal pressure, vocalization, coughing, or lifting a heavy weight. Mechanical or heat stimulation of any skin area causes an extremely sensitive reaction, and the muscle contracts reflexively.B. Activity of individual NMU1. At a room temperature in which the subject feels no cold and under ‘at rest’ state, only the tonic discharges are obtained with spike amplitudes of about 300μV and current duration of less than 5 msec. The frequency of the discharge is of the order of 3 to 4 c.p.s.(cf. for M. soleus 8 to 10 c.p.s.). The tonic dis-charge can be led out more frequently from the deeper layer.2. Increased constriction involves kinetic discharges, with amplitudes of 600 to 800 μV (far smaller than the soleus); these discharges seem to originate in the shallower layer.3. The _??_-S curve dissolves into two distinctly different components: one has the plateau with S=8 msec. extending to 170 msec., hence ascends sharply, while the other maintains its plateau at the level of S 15 msec. and proceeds far beyond, up to 260 msec., where it makes a gradual rise. The former corre-sponds to the discharges of the kinetic NMU and the latter to the tonic ele-ments. In the _??_-S diagram the anal muscle occupies the extreme right position among the muscles so far investigated.