I do believe you are asking about a sarcomere, units of repeating bands that make up the fibers (myofibrils) of a striated muscle.
form a muscle cell
The organization of contractile proteins into a regular end-to-end repeating pattern of sacromeres along the length of each cell accounts for the striated, or striped, appearance of skeletal muscle in longitudinal section.
the branching pattern increases the strenght of the muscle allowing it to pump blood to all cells in the body
A skeletal muscle cell is a cell of a skeletal muscle.
A muscle cell is a cell which can change length
No a muscle cell is a somatic cell
muscle
Actin and myosin are contractile proteins found within muscle fiber. If you look at a muscle fiber under a microscope it is made up of several repeating units called sarcomeres that run along the length of the muscle fiber. Proteins actin and myosin are found in the sarcomeres in different locations.
A muscle is neither a cell nor a organ, it is a muscle
Sarcomere
A muscle cell
muscle cell