Electromyographical Studies on the Motor Innervation of Toad's Sartorius Muscle : (I) The Size of Motor Unit and Its Relation to Fasciculus

The motor unit was defined first by Sherrington 1l as follows: the muscle with its nerve may be thought of as an additive assemblage of motor units, meaning by a motor unit an individual nerve with bunch of muscle fibres it activates.The size of an average motor unit has been determined by dividing the number of fibres in muscle by that of motor fibres in its nerve.But, many investigators in early periods in this field, Reichert 23 l (1951), Tergast 26 l (1886), Lucas 19 J (1906) counted the number of total nerve fibres contained in its nerve, so that the size they obtained may be smaller than the real value of the motor unit.Later, Clark 4 J (1931), Van Harreveld 11 J (1934) determined the real size of a motor unit after deafferenting.The author intended to solve this problem of motor unit by an e!ectromyographical method, measuring the muscle action potentials of various unit (motor unit, BFT unit etc.).Related to this problem, ramification of the motor nerve fibre supplying the sartorius muscle and innervation of a single fasciculus were also studied.Finally, the relation of the motor unit to the fasciculus was discussed.METHOD Sciatic-sartorius preparations of Japanese toads (Bujo vulgaris) were used.Various stimulating methods for evoking the muscle action potential were selected case by case, e.g.applying isotonic sodium citrate solution (1.96%) to a desheathed sciatic nerve, injection of the solution into the nerve trunk, applying a single electroshock to nerve or muscle directly and immersing the muscle into Biedermann's solution.For leading of muscle action potential evoked in various ways, Sugi's septal method or its modified methods were utilized.Action potentials were led to a cathod ray oscilloscope through a 4 staged amplifier and were photographed.