Protoplasma, 8 311
- J. BBLEHRADKK
- CLARK, A. J. (1920). Journ. Pkysiol. 54, 275…
THE responsive mechanism by which a muscle cell reacts to a stimulus consists of a group of closely associated processes following each other at definite intervals. Three distinct phases may be recognised in this system: (1) a local process occurring in the region of the stimulus; (2) a rapid series of changes referred to as the propagated disturbance and indicated by the bio-electric variation; (3) the response of the cell in the region adjacent to the seat of stimulation. Associated with each of these phases are various processes which, although separately definable, appear to be integral parts of the whole response. Thus, with the first and second phases are associated chronaxie, the bio-electric variation, the conduction of the propagated disturbance, the absolute and relative refractory periods, and other phenomena. With the third phase, comprising the contraction of the muscle, are associated the latent period of contraction, the duration of the contractile phase, the duration of the relaxation phase, the tension developed, and the heat production. Considerable evidence exists that these are inter-dependent processes and not merely independent concurrent processes (Lillie, 1923; Fulton, 1926). In comparing the velocity of movement of different muscles it has been observed that the more rapid is the movement of the tissue the briefer are chronaxie, the time for the conduction of the propagated disturbance, the time for the development of the bio-electric variation, the duration of the refractory period, the duration of the latent period, and the duration of the isometric contraction. It has been shown also that with the increase of initial tension on the muscle there is associated an increase in chronaxie, in the duration of the isometric twitch, in the total tension, and in the heat production.