Explain the steps involved in the contraction of a skeletal muscle fiber.

Every time we move, the muscles contract and relax. Even for a few seconds, it is a fairly complex process.

The cells that make up the skeletal muscle are called muscle fibers or myofibers and are long cylindrical structures surrounded by a plasma membrane called sarcolemma.

Each muscle cells contains thousands of myofibrils, formed by thin filaments (actin) and thick filaments (myosin), which interact to produce shortening of the muscle, contraction.

Muscle contraction is the result of the molecular interaction that occurs between the proteins (actin and myosin) that form the filaments contractile, leading to a slippage of the fine filaments on the thick filaments.

It can be divided as follows:

- The calcium that is outside the muscle cell enters through the cell membrane.

- Calcium, already inside the muscle cell, joins the actin and makes it rotate so that it can be anchored.

- Actin binds to the myosin head, then inorganic phosphate comes out of the myosin head that produces a change in volume.

- This volume change of the myosin head causes it to change from 90 degrees to 45 degrees.