Stimulus rhythm in reflex tetanic contraction

Abstract

When an afferent nerve is stimulated by single shocks following each other in not too fast succession the resulting reflex tetanus shows tensile vibrations corresponding with the rhythm of the stimulation. We find that the upper limit of stimulus frequency at which incompleteness of fusion of the component reflex contractions is still traceable differs considerably for different types of reflex. Method .—Our observations have been upon the mammalian preparation (cat) in the decerebrate condition. Transection of the brain-stem between the anterior and posterior colliculi was performed under complete chloroformanæsthesia, and the whole of the brain anterior to the transection removed. For purely spinal reflexes the level of the spinal cord transection lay variously between 12th thoracic and 3rd lumbar segments, the preparation being also decerebrate. In some instances the spinal section was performed, under full anæsthesia and asepsis, four to eight days prior to the decerebration. For use with the myograph the contracting muscle was in all cases isolatedly attached to it, and all other muscles in both hind limbs immobilized by appropriate nerve-section or resection. Fixation of the limb was obtained by steel drills in femur and tibia, a strong clamp holding the pelvis. For stimulation induction shocks were used, these being (except where otherwise stated) single shocks at frequencies varying from 35-95 per sec. For obtaining single-shock series of these frequencies a special key ( see Appendix) had been devised (C. S. S.) separating the make- and break-shocks of the ordinary inductorium, from which its spring interrupter had been removed. For most of the observations the primary coil was coreless, and the break-shock was given by short circuiting the primary coil, the current in the unshorted primary being usually 70 milliamps. The stimulating electrodes were 10 mm. apart with anode in all cases toward the cut end of the stimulated nerve. The isometric myograph was similar to that previously described. Its vibration rate when unattached to the muscle was over 1000 per sec.