how do muscle cells contract?include the relationship between actin and myosin?

The brain controls everything.

The ability of eucaryotic cells to adopt a variety of shapes and to carry out coordinated and directed movements depends on the cytoskeleton, a complex network of protein filaments that extends throughout the cytoplasm. This "cytomusculature" is responsible for the crawling of cells, muscle contraction, the changes in shape during the development of a vertebrate embryo, etc. Organelles move along it through the cytoplasm. These structures are not found in bacteria.
The actin based structures were first discovered in muscle where muscle contraction is the most familiar action. Running, walking, swimming, and flying depend on the rapid contraction of skeletal muscle, while the pumping of the heart and gut peristalsis depend on the contraction of cardiac and smooth muscle, respectively.

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