The single-unit smooth muscles are:

The given figure represents the cross-bridge cycle in skeletal muscle. What does step $B$ in the figure represent?

Assertion: Fatigue is the inability of a muscle to relax.
Reason: It is due to lactic acid accumulation by repeated contractions.

Assertion : The phase of muscle contraction occurs when myosin binds and releases actin.
Reason : Muscle contraction is initiated by a signal sent by the peripheral nervous system via motor neuron.

Which of the following ions is essential for muscular contraction?

In the mechanism of muscle contraction or shortening of muscle,the . . . . . . get reduced whereas the . . . . . . retain the length.