Transmission of Impulses from Nerve to Muscle Fibre

Abstract

Summary. Direct application of different substances to the motor end plate of lizard muscle led to the following results: Acetylcholine (threshold 5 × 10 ‐6 μg) initiates a short twitch‐like contraction. After the first application, the end plate is refractory to further doses and to electric stimulation of the nerve. Direct electric stimulation of the end plate and application of potassium (threshold 10 ‐4 μg) or rubidium are still effective. Potassium or rubidium do not show any blocking action, as does acetylcholine. Acetylcholine and potassium applied to the fibre substance have no effect even in a tenfold concentration. Acetylcholine, potassium, and other stimulating substances cause a decrease in the end plate — fibre potential. The threshold of the motor end plate is not altered by poisoning with veratrine. Just as total muscle, the veratrinized fibre reacts to stimulation with protracted contractions. In the first stage, curarine blocks the end plate for nerve impulses and for acetylcholine, while direct electric stimulation of the end plate and application of potassium are still effective. In a later stage, the excitability in response to these stimuli is abolished, only the direct excitability of the fibre substance is retained. The present material supports the assumption of two boundary aces in the motor end plate. The present work has been supported by grants from the Carlsberg Foundation and the Michaelsen Foundation.