What does $HMM$ stand for in the context of muscle structure?

Cardiac muscle fibers differ from skeletal muscle fibers in that they are -

Muscle fatigue occurs due to the accumulation of:

How is the meromyosin formed?

Arrange the following steps of muscle contraction in the sequence of events occurring first:
$I.$ Receptor sites on sarcolemma
$II.$ Nerve impulse
$III.$ Release of $Ca^{2+}$
$IV.$ Acetylcholine release
$V.$ Shortening of sarcomere
$VI.$ Synaptic cleft
$VII.$ Spread of impulse over sarcolemma on $T$-tubule
The correct option is:

The actin filament is shown below. Where does $Ca^{++}$ bind during muscle contraction?