Abstract
1. Electrical responses of isolated leaf-like receptors in the frog sartorius muscle to muscle stretch were recorded by means of the paraffin gap method.
2. The sensory terminal is always positive by 0.25 to 1mV to the proximal portion of the axon. The magnitude of the steady potential decreases with increase in the terminal-gap distance. Crushing of the axon, especially under the paraffin pool, yields large changes of the steady potential.
3. A slow potential like a spindle potential in the muscle spindle receptor was observed during muscle stretch. The deflection was negative in some cases and positive in others, and the direction of the deflection was often changed by the movement of the axon in the paraffin pool during muscle stretch.
4. Monophasic and triphasic spikes occurred superimposed on the slow potential during muscle stretch of supra-threshold strength, when recordings of potential changes were made across the paraffin gap situated at a point along the axon less than 1mm from the isolated end of the nerve. The amplitudes of the monophasic spike and of each peak in the triphasic spike except the notch decreased exponentially with increase of the terminal-gap distance from 2 to 7mm. Consequently, it has been considered that the notch may be due to the conductive impulse while the others may be local activities originating near the sensory terminal or may consist of both the local activity and the conductive spike.
5. The slow potential and the local activities during muscle stretch were discussed in relation to a generator potential or a trigger mechanism in the mechanoreceptor.
