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

Contraction of muscles is the best example of conversion of cellular energy into

Choose the correct statements regarding muscle contraction. $A$. $A$ motor neuron carries a signal sent by the Central Nervous System $(CNS)$ to the sarcolemma of the muscle fibre. $B$. The neural signal generates an action potential which causes the release of $Ca^{++}$ into sarcoplasm. $C$. Increase in $Ca^{++}$ inactivates the actin for breaking cross bridges. $D$. Actin binds to the myosin head to form a cross bridge. $E$. Shortening of sarcomere takes place,by pulling actin filaments towards the centre of '$A$' band. Choose the correct answer from the options given below:

Arrange the following steps of muscle relaxation in the correct chronological sequence:
$I.$ $Ca^{2+}$ ions are pumped back to the sarcoplasmic reticulum.
$II.$ $Z$-lines return to their original position.
$III.$ Masking of actin filaments occurs.
$IV.$ Relaxation of muscles.

Contraction of muscle fibre takes place by the sliding of $:-$

$I-$bands of myofibrils are bisected by