Which one of the following types of muscle fibers will be the first one to undergo fatigue?

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

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:

Which ions must be present for the binding of cross-bridges during muscle contraction?

'Oxygen debt' is the amount of oxygen required for

Contractile tissues have the following features:
$(i)$ Mesodermal in origin
$(ii)$ They contain stretch receptors
$(iii)$ Rhythmic contractions are seen in them
$(iv)$ They do not fatigue during the life of the animal
Which of the above are characteristics of sphincters?