Flexion of the thigh,knee,and their rotation is facilitated by:

The contractile protein of skeletal muscle involving ATPase activity is

Given below are two statements $:-$
Statement-$I$ :- Each organised skeletal muscle in human body is made of a number of fascicles,held together by a common connective tissue layer called fascia.
Statement-$II$ :- The portion of the myofibril between two successive '$Z$' lines is considered as the functional unit of muscle contraction,known as a sarcomere.
In the light of the above statements,choose the correct answer from the options given below $:-$

How does a muscle shorten during its contraction and return to its original form during relaxation?

Analogy type questions:
$(1)$ Red muscle fibers / White muscle fibers have fewer mitochondria but more sarcoplasmic reticulum.
$(2)$ When nerve impulses reach the neuromuscular junction,acetic acid / acetylcholine neurotransmitter is released.

Voluntary muscle is present in