Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction.

Which of the following statements are false regarding the muscle structure?
$I.$ In the centre of each $I$-band is an elastic fibre ($Z$-line) which bisects it.
$II.$ Thin filaments are firmly attached to the $Z$-line.
$III.$ $M$-line is a fibrous membrane in the middle of $A$-band.
$IV.$ $A$ sarcomere comprises one full $A$-band and two half $I$-bands.

Which characteristic is $NOT$ associated with white muscle fibers?

Describe the important steps in muscle contraction.

The contractile protein of skeletal muscle involving ATPase activity is

Based on their location in the human body or animals,the types of muscles are:
$I.$ Skeletal
$II.$ Visceral
$III.$ Cardiac
$IV.$ Non-visceral
The correct option is: