MULTIPLE MOTOR INNERVATION OF THE FROG'S SARTORIUS MUSCLE

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Abstract
Exptl. evidence is described for the existence of multiple motor nerve endings in most fibres of the frog''s sartorius muscle. The electric response of the muscle to a maximum nerve stimulus is recorded. In both pelvic and tibial regions a large, synchronous spike of about 50 mV and short latency (1-2 msec.) is usually obtained. This seems incompatible with the facts that the motor nerve endings are distributed over a length of about 2.5 cm. and that most of the sartorius fibres run through the whole length of the muscle. The apparent discrepancy is due to the presence of multiple (2 or 3) motor nerve endings on most fibres. Muscle impulses are set up simultaneously at these junctional regions of each fibre; only the impulses which arise nearest to the amplifier leads are recorded, since those more distal are blocked by collision. This can be demonstrated by cutting one of the 2 main nerve branches, by partial curarization, by submaximal nerve stimulation, and by combined application, at suitable time intervals, of 2 stimuli (i) to the motor nerve and (ii) to the nerve-free pelvic end of the muscle. By all these procedures, some myoneural junctions are put out of action and, therefore, some of the "distal" impulses (arising far away) can travel unhindered to the recording leads. In this way, a part or the whole of the normal, synchronous and early spike potential is abolished and replaced by a discrete potential wave of long latency.

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