Contraction of a muscle is caused by

Which part of a muscle cell is the storehouse of calcium ions?

Lack of relaxation between successive stimuli in sustained muscle contraction is known as

If a muscle fails to give stimulation action and there is much ingestion of lactic acid,the condition is termed as

$A-$ 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.

The largest number of muscles in the human body is found in which region?