In the muscle calciumions are
stored the sarcoplasmic
reticulum. a motor neuron
stimulus for the contraction
neurotransmitters called
are released in neuromuscular
junction and sarcolemma is excited.

excitation is conduced the
sarcoplasmic reticulum then
realeases calcium into the
sarcomeres.

the sarcomeres the ions bind
to molecules associated to
activating myosin binding of
actin. The , then able to to
actin, pulls protein and the
shortens. The summation
simultaneous contraction of
and myofibrils constitutes muscle
contraction. During relaxation
the calcium return back to
sarcoplasmic reticulum.

For to bind to , and thus for
contraction to occur, of
one ATP is necessary. During
the return of ions to
the reticulum is an
process that spends too. So both
contraction and relaxation
energy-spending processes.