Question

If muscle fiber concentration is all-or-none, how is graded muscular activity possible?

Answer 1

Answer :)

The muscular activity depends upon the action potential. If a particular action potential crosses, threshold voltage, the muscle contraction occurs. This is all condition. If it does not cross the threshold, there will be no contraction. This is none condition irrespective of how strong stimulus is.

However, graded muscle activity depends upon the strength of the stimulus. There are two graded responses. In wave summation, a strong twitch follows by a weaker incomplete twitch. Therefore, continuous stronger twitches make the wavy contractions. Other is tetanus in which if stimulus frequency is quick but having a relaxation phase, produces incomplete tetanus. If stimulus frequency is so high that the relaxation phase is disappeared, it produces complete tetanus.

Therefore, in graded muscles, the action potential should cross the threshold and then it will call as the all condition of all or none law.