When a spider weaves a web, this is an innate, or instinctual action. A spider needs no training from other spiders (including its parents) to know how to spin a web.
The process of muscle contraction requires several steps.
The most famous theory on how the contraction and relaxation of muscles take place is the sliding filament theory.
However, this theory has been refined and one important addition to it is the mechanism by which myosin can pull actin and cause shortening of the sarcomere.
For the movement of myosin, it binds and releases actin and forms cross bridges.
Myosin is subdivided into two regions - S1 and S2. The contraction of the S1 region is what constitutes the power stroke.
An important requirement of the power stroke is the hydrolysis of ATP to release an inorganic phosphate which provides energy for the process.
