. Elementary physiology. Physiology; Physiology. 70 Elementary Physiology. the response of a muscle to electrical stimulation may be obtained.^ In- duced currents from a secondary coil are made use of, and these are conveyed to the nerve by two wires, called electrodes, placed parallel to each other and about -j^ of an inch apart. The electrodes are joined up to the terminals of the secondary coil, and the nerve laid across them. On making or breaking the electric current in the primary circuit, a tran- sitory current is induced in the secondary circuit, which excites the nerve and starts a ne
. Elementary physiology. Physiology; Physiology. 70 Elementary Physiology. the response of a muscle to electrical stimulation may be obtained.^ In- duced currents from a secondary coil are made use of, and these are conveyed to the nerve by two wires, called electrodes, placed parallel to each other and about -j^ of an inch apart. The electrodes are joined up to the terminals of the secondary coil, and the nerve laid across them. On making or breaking the electric current in the primary circuit, a tran- sitory current is induced in the secondary circuit, which excites the nerve and starts a nerve impulse, and this in turn excites the muscle to con- tract. • The muscle is fixed at one end, and its other end is attached by a thread to the short end of a lever. When the muscle contracts the lever. Fig. 49.—Simple muscle curve. The nerve attached to the muscle was stimulated at a, and at b the muscle began to contract. The period occupied by the interval between a and b is termed the " latent ; The lower tracing, taken by a writing-point attached to a vibrating tuning-fork, shows j^o second intervals ; the small undulations upon it are due to overtones. moves, and, by means of a writing-point attached to its long end, traces a curve on a smoked surface of paper which is caused to move past the writing-point. When a single electric stimulu? is applied to the nerve, the tracing obtained of the muscular contraction is similar to that shown in Fig. 49. There is first a very short pause before the contraction begins, called the latent periody then the contraction begins, and is followed by the relaxation. The relative times occupied by the periods of contraction and relaxation vary with the load against which the muscle contracts; but the total period of contraction and relaxation is fairly constant, and amounts approximately to -/g second. If now the stimulation be given rhythmically at regular periods, the effect produced will vary according to the rap
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