The Reaction of Striated Mammalian Muscle to Variations of the Parameters of Electrical Stimuli Applied to Nerre and Muscle Investigated with Special Regard to Experimental Technique

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Abstract
Summary.: The reaction of striated mammalian muscles to electrical stimdation of nerve and muscle has been studied with special reference to the effect of variations in the parameters of the stimulus on the muscular response. Experiments were performed on isolated phrenic nerve diaphragm preparations and on the gastronomic and the flexor digitorum longus muscles of rabbit in situ. 2)The absolute refractory period of the flexor digitorum longus muscle following directly applied stimuli of 0.4 msec. has been determined to range from 1.3 to 1.6 msec. Prolongation of the pulse length to 2 msec. caused an increase of the absolute refractory period up to from 2.2 to 2.3 mseo. When the interval between two successive short nerve volleys was less than the absolute refractory period of the muscle, an additional electrical and mechanical response could be set up in the muscle by the second volley. On use of single nerve impulses shorter than the absolute refractory period of the muscle, additional electrical and mechanical responses could also be caused by the break stimuli. This effect has been shown to be a result of the reduced conductivity of the nerve fibres during the first 2 nisec. after the conditioning shock. Application of direct electrical stimulation to fully curried muscle gave the following results: For impulses shorter than 3 msec., single sub maximal and maximal contractions were obtained. When the maximal niveau was reached, increase of the stimulating current usually did not cause any further augmentation of the muscle response. It has been concluded that, with this form of direct stimulation, the muscle fibres respond to the stimulus in an “all‐or‐nothing” manner. It is therefore possible by this method to investigate changes of the irritability as well as the contractility of the muscle itself. With single impulses of 3‐6 msec. duration, additional con‐tractions were elicited by the stimulus on current break. Single impulses of even longer duration caused repet3tive firing.