$A$ human body contains how many muscles?

Identify the bands $P, Q,$ and $R$ in the given diagram.
$\quad\quad\quad P \quad\quad\quad Q\quad\quad\quad R$

The functional unit of the contractile system in the striped muscle is

$A$: 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.

Aerobic muscles are called $...A...$ and anaerobic muscles are called $...B....$ Here $A$ and $B$ refer to:

Which muscle component is the smallest among the given options?