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The cross bridge cycle is the series of events
during which myosin heads pull thin ﬁlaments toward the
center of the sarcomere.
Cross bridge formation.
myosin head attaches to an actin
myoﬁlament, forming a cross bridge.
The power (working) stroke.
ADP and P
are released and the myosin head pivots
and bends, changing to its bent low-energy
state. As a result it pulls the actin ﬁlament
toward the M line.
Cross bridge detachment.
attaches to myosin, the link between myosin
and actin weakens, and the myosin head
detaches (the cross bridge “breaks”).
Cocking of the myosin head.
As ATP is
hydrolyzed to ADP and P
, the myosin
head returns to its prestroke high-energy,
or “cocked,” position.
This cycle will continue as long as ATP is
available and Ca
is bound to troponin.
In the absence
of ATP, myosin
heads will not
Cross Bridge Cycle