Refractory Period and Conduction Velocity of the Striated Muscle Fibre*

Abstract Buchthal, F. and L. Engbæek, Refractory Period and conduclion velocity of the striated muscle fibre. Acta physiol. scand. 1963. 59. 199–220. —Refractory period and conduction velocity of transmembrane potentials were determined in single frog muscle fibres by intracellular stimulation and recording at 14, 20 and 25° C. At the end of the absolutely refractory period the latency of the potential evoked by the second stimulus was substantially increased mainly due to a reduction in conduction velocity, delayed firing causing at most 10 per cent of the total delay. The absolutely refractory period terminated at the onset of the negative after potential, recovery in excitability, amplitude and conduction velocity in the relatively refractory period occurred within a time interval in which the membrane potential did not change more than about 3 mV. At 2–3 times the absolutely refractory period excitability and conduction velocity had a supernormal phase. At the absolutely refractory period the level of depolarization required to initiate a propagated response had increased from 40 to more than 60 mV (recorded 0.25–0.6 mm from the stimulating electrode). A local response appeared at a time interval of 70–80 per cent of the absolutely refractory period of the propagated response.