Striated muscles contract by

Both proteins,actin and myosin,are arranged in a rod-like structure in the muscles:

Which mineral element is essential for muscle contraction?

Given below are two statements:
$Statement-I$: Plasma creatinine is produced during catabolism of creatinine phosphate in skeletal muscle contraction.
$Statement-II$: Creatinine phosphate provides a ready source of high-energy phosphate.
In the light of the above two statements, choose the most appropriate answer from the options given below.

Which of the following are the special properties of muscles?

$A$: Latent period is the interval between the application of an appropriate stimulus and the initiation of contraction.
$R$: Latent period is minimum in cardiac muscle fibres.