Question

1. Only a portion of the duration of a single twitch includes increasing tension within a muscle fiber.
   1. What are the three main phases/periods of a muscle contraction?
   2. During which portion(s) (name the period) of a twitch is tension NOT increasing. Clearly explain why in each case.

c. What are all the steps involved in a single twitch that happen during this period without tension?

Answer 1

a. What are the three main phases/periods of a muscle contraction?

Ans: Muscle Contraction has three phases.

1. Latent period (lag phase)

This starts at the point of stimulus, includes action potential and release Ca2+ ions. Contraction is generated by a single action potential called a muscle twitch. This period is a short delay of 1-2msec.

2. Contraction phase

Cross-bridges between actin and myosin are formed.Myosin releases and reforms cross-bridges as the sarcomere shortens and muscle contracts. Durig this period ATP is used.

3. Relaxation phase.

Muscle relaxation results in decrease of tension. During this phase calcium is actively transported back into the sarcoplasmic reticulum at the cost of ATP.

b. During which portion(s) (name the period) of a twitch is tension NOT increasing. Clearly explain why in each case.

Ans:

Isotonic Contractions

Isotonic contractions maintain constant tension in the muscle w.r.t change in muscle length. Occur when a muscle’s contraction exceeds total load on the muscle. These contractions can be the following.

Concentric Contractions

It is a muscle contraction in which the muscles shorten while generating force. Such contractions alter the angle of the joints to which the muscles are attached.

Eccentric Contractions

Eccentric contraction results in increase in the length of a muscle. These contractions can be voluntary and involuntary. During this, muscle elongates while under tension due to an opposing force which is greater than force generated by the muscle.

Relaxation phase. Muscle relaxation phase results in decrease of tension. During this phase calcium is actively transported back into the sarcoplasmic reticulum at the cost of ATP.

c. What are all the steps involved in a single twitch that happen during this period without tension?

Ans:

Isotonic Contractions

Isotonic contractions maintain constant tension in the muscle w.r.t change in muscle length. Occur when a muscle’s contraction exceeds total load on the muscle. These contractions can be the following.

Concentric Contractions

It is a muscle contraction in which the muscles shorten while generating force. Such contractions alter the angle of the joints to which the muscles are attached.

Eccentric Contractions

Eccentric contraction results in increase in the length of a muscle. These contractions can be voluntary and involuntary. During this, muscle elongates while under tension due to an opposing force which is greater than force generated by the muscle.