$A$ sarcomere consists of

$A$: Application of stimuli repeatedly just at the start of relaxation of a muscle fibre shows an increase in the extent of contraction initially and results in treppe or staircase phenomenon.
$R$: It can be attributed to the summation effect of the sub-threshold stimuli being given again and again.

Which of the following activities occurs at the site labeled $P$ in the given diagram of a myosin monomer?

Between two successive $M$-lines,there is/are:

Arrange the given steps of muscle contraction in the series of events from first to last.
$I.$ Myosin head binds to the exposed active site on actin to form a cross bridge.
$II.$ The $Z$-line attached to these actin are also pulled inwards,thereby causing shortening of sarcomere,also called contraction.
$III.$ This pulls the attached actin filaments towards the centre of $A$-band.
The correct option is:

The region at the ends of the $A$-band of two adjoining sarcomeres is called