The Effects of Splanchnic Stimulation on the Contraction of Fatigued Muscle
When skeletal muscle is repeatedly stimulated by a long series of rapidly recurring electric shocks, its strong contractions gradually grow weaker until a fairly constant condition is reached. The record then has an even top—the muscle has reached the “fatigue level.” The effect of splanchnic stimulation was tried when the muscle had been fatigued to this stage. The effect which was often obtained by stimulating the left splanchnic nerves is shown in [Fig. 11]. In this instance the muscle while relaxed supported no weight, and while contracting lifted a weight of 125 grams. The rate of stimulation was 80 per minute.
Figure 11.—Upper record, contraction of the tibialis anticus, 80 times a minute, lifting a weight of 125 grams. Lower record, stimulation of the left splanchnic nerves, two minutes. Time, half minutes.
The muscle record shows a brief initial rise from the fatigue level, followed by a drop, and that in turn by another, prolonged rise. The maximum height of the record is 13.5 millimeters, an increase of 6 millimeters over the height recorded before splanchnic stimulation. Thus the muscle was performing for a short period 80 per cent more work than before splanchnic stimulation, and for a considerably longer period exhibited an intermediate betterment of its efficiency.
The First Rise in the Muscle Record
The brief first elevation in the muscle record when registered simultaneously with arterial blood pressure is observed to occur at the same time with the sharp initial rise in the blood-pressure curve (see [Fig. 12]). The first sharp rise in blood pressure is due to contraction of the vessels in the area of distribution of the splanchnic nerves, for it does not appear if the alimentary canal is removed, or if the celiac axis and the superior and inferior mesenteric arteries are ligated. The betterment of the muscular contraction is probably due directly to the better blood supply resulting from the increased pressure, for if the adrenal veins are clipped and the splanchnic nerves are stimulated, the blood pressure rises as before and at the same time there may be registered a higher contraction of the muscle.
Figure 12.—Top record, arterial blood pressure with membrane manometer. Middle record, contractions of tibialis anticus loaded with 125 grams and stimulated 80 times a minute. Bottom record, splanchnic stimulation (two minutes). Time, half minutes.