Sarcolemma is a membrane found over in

Relaxation of the muscle takes place due to
$I.$ Pumping of $Ca^{2+}$ ions into the sarcoplasmic reticulum
$II.$ Presence of $ATP$
$III.$ Conformational changes in troponin and masking of the actin filament
Which of the following options contains the correct statements?

$A$: Muscle tetanus is the phenomenon of sustained contraction of a muscle due to a succession of nerve impulses/stimuli being received by it.
$R$: Many of our daily activities are due to tetanic contraction of muscles,such as holding a book.

The interval between the beginning of the electrical response and the peak of tension recorded is known as the:

Which of the following ions is essential for muscular contraction?

In the thin filament of skeletal muscle fibre,a small globular protein that masks the active sites for myosin on the $F-$actin,is