Mechanical

The Heatproduction in Prolonged Contractions of an Isolated Frog’s Muscle

The paper shows that the time span is called the latent period which is short and constant for skeletal muscle fibers such as the frog Gastrocnemius muscle. Hence it is the ideal tissue for such studies.
Ans: The contraction of a muscle fiber produced by a single action potential is called a twitch. A simple twitch is composed of three components – the latent phase, the contraction phase, and the relaxation phase. The latter two phases have a measurable duration. The latent phase is the first phase where there is a delay due to the combination of initial inertia due to electric delay in the isolated sciatic nerve-Gastrocnemius muscle preparation and the stimulating external electric circuit as well as the inertia in the recording apparatus attached. The latent phase also exists in the in vivo conditions in the live animal where it is governed by the natural physiological status and is free from external influences in the experiment. Hence it is slightly shorter in the living animal. The contraction phase is the one when there is an actual shortening of the muscle fibers as a response to the electrical and biochemical stimulus at the motor nerve endplate. The relaxation phase is the passive phase where the muscle recovers to its original state and shape by its endogenous elasticity. It is a mere mechanical process. The total time of a simple twitch lasts usually from 0.1 to 0.2 seconds.
Ans: The simple twitch when recorded at room temperature (22°C) gave a total cycle duration of 400 msec (milliseconds) which comprised of the contraction phase of 80 msec and the relaxation phase of 320 msec. At 4°C, the total time was increased to almost double at 760 msec (160 msec contraction and 600 msec relaxation phase times). On increasing the temperature to 30°C, both the times decreased considerably (100msec contraction and160 msec relaxation phase times giving a total duration of the twitch at 260 msec). The results imply that the muscle responds more quickly at warmer&nbsp.temperatures.

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