ELECTROMYOGRAPHIC STUDIES ON THE FUNCTION OF THE EXTERNAL SPHINCTER MUSCLE OF THE ANUS : I. GENERAL PROPERTIES OF THE EXTERNAL SPHINCTER MUSCLE OF THE ANUS
1962 Volume 24 Issue 2 Pages 81-87
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1962 Volume 24 Issue 2 Pages 81-87
Electromyographic experiments were carried out on dogs to clarify the properties of the external sphincter muscle of the anus. Successive discharges of single NMUs were led off by paired silver needle electrodes inserted with an interelectrode distance of 1.0 to 1.5cm. The discharge-interval-time-series of the respective NMU was analyzed by the conventional method. The results obtained are summarized as follows. 1. The τ-S curve of the external sphincter muscle of the anus was situated on the right side with a longer horizontal and a more slowly ascending part than that of the muscles of the hind limbs of the dog in normal standing. It may be considered from the fact that the spincter muscle was activated chiefly by the spinal nervous system. 2. In the case of the other postures (recumbent, supine, prone, and sitting) examined, the situation of the τ-S curve on the correlative chart was displaced generally to the left side. It is considered that the displacement of the curve depends upon the increased activation of the motor area in the cerebral cortex regulating the activity of the muscle. 3. While the dog maintained a forward- or backward-inclined standing posture on the tilting board, the distribution of τ-S points altered its situation to the left side. 4. There were also individual differences in situation between the τ-S curves. 5. Marked changes occured in the discharge intervals of a single NMU during the seesaw movement of the board, on which the dog stood, made by lifting or sinking its end. The order of such changes was as follows: N→F→N→F→N→F→N in experiment 1. N→B→N→B→N→B→N in experiment 2. (N: normal, F: forward-inclined, and B: backward-inclined standing posture) In other words, the shortening of the discharge intervals was observed in both experiments. A particularly marked decrease was seen in the width of the irregular fluctuation in experiment 2.
