Muscle fatigue occurs due to the accumulation of . . . . . . .

$A-$ Visceral muscles do not show any striations and are smooth in appearance. Hence,they are known as non-striated muscles.
$R-$ Their activities are under the voluntary control of the nervous system.

Which one of the following takes place in a myofibril when skeletal muscle contracts?
$A$-band (Dark band) | $I$-band (Light band) | $H$-zone

Striated muscles contract by

Which of the following statements are correct regarding skeletal muscle?
$A$. Muscle bundles are held together by a collagenous connective tissue layer called fascicle.
$B$. Sarcoplasmic reticulum of muscle fibre is a storehouse of calcium ions.
$C$. Striated appearance of skeletal muscle fibre is due to the distribution pattern of actin and myosin proteins.
$D$. $M$ line is considered as the functional unit of contraction called sarcomere.
Choose the most appropriate answer from the options given below:

Which protein is both structural and enzymatic?