Question

Which statements are true of summation?

a) A second nerve stimulus occurs before the muscle has had time to relax (i.e., before cell Ca²⁺ concentration has been restored to resting values).

b) A second stimulus is delivered while the nerve axon is depolarized.

c) A second stimulus occurs while the muscle cell membrane is depolarized.

d) More motor units are recruited.

Draw the appropriate force/tension response of skeletal muscles in the images below. 4 pts Twitch Summation Incomplete tetanus Complete tetanus Tension (N) 100 200 300 400 100 200 300 400 À 100 200 300 400 100 200 300 400 4 Time (ms) Annotate Start Over

Answer 1

Option a and d are true statements.

A second nerve stimuli occur before the muscle has time to relax. And more motor neurones are recruited.

In the first stimulus the muscle contracts. But there is a refractory period when the muscle continuous in the contraction where no other stimulus can contract. Soon after it a second stimulus can contract the muscle again. Now the muscle wont get time to relax. Initially few motor units were used. But later as the stimuli leads to more contraction more motor units gets involved.

Twitch summation, Incomplete Tetanus complete Tetanus Tension mm Time