How do muscle cells work?

Hint: Muscle cells are specialised cells in the animals which can contract by the help of motor proteins. These cells are known as myocytes. The muscle cells are long as compared to the other cells and they collectively form muscle tissue.

Complete answer:
Muscle cells produce push and motion. It contains protein filament called actin and myosin. The calcium ion is very much essential for muscle cell contraction. The calcium ion helps in establishing interaction between the actin and myosin.

The calcium ion binds with the C component of the actin filament. This opens the binding site for the myosin to bind and stimulate contraction. The contraction in the muscle cell causes contraction.
The troponin in the absence of calcium ion binds with the tropomyosin and masks the myosin binding site on the actin filament. This causes relaxation of the muscle cells. In the presence of calcium ion, troponin will release tropomyosin and tropomyosin remains unbind.

When the myosin binds at the actin filament, the energy is used in order to crawl over the actin till the Z plate is reached and the cell attains full contraction. Once the full contraction is reached, the calcium is released and the tropomyosin again binds the myosin head and causes relaxation.

Hence, the correct answer is option ()

Note: The small units containing actin and myosin which are able to slide over one another known as sarcomere. The muscle cells contain mitochondria which fulfils the demand of energy and the sarcoplasmic reticulum which secretes/provides calcium ion needed for the muscle contraction.