In a single muscle twitch, the contraction period:

Question

A. is from start of contraction to the end.

B. is from the start of contraction to peak of contraction.

C. is from the peak of contraction to the end 

D. is the peak of contraction

Answer 1

A. is from start of contraction to the end.

The reason is because we have four separate phases of muscle contraction:

1. The latent period- the time required for the release of Ca ²⁺.
2. The contraction period- the time during actual muscle contraction.
3. The relaxation period -the time during which Ca ²⁺ are returned to the sarcoplasmic reticulum by active transport.
4. The refractory period- the time immediately following a stimulus. This is the time period when a muscle is contracting and therefore will not respond to a second stimulus. Since this is occurring at the same time as the contraction, it does not appear on the myogram as a separate event.