The Muscular System

The muscular system consists of an extensive network of muscles and related tissues that supports movement, posture, and many other bodily processes. It includes more than 600 muscles connected to bones and other structures throughout the body.

Muscles create movement by contracting and relaxing in response to signals from the nervous system. These actions allow us to move our arms and legs, make facial expressions, and breathe. Muscles also help stabilize the body, produce heat, and support and protect internal organs.

Within each muscle are individual fibers arranged in bundles known as fascicles. These fibers contain myofibrils, which consist of smaller repeating units called sarcomeres. Inside the sarcomeres, proteins called actin and myosin work together to generate muscle contractions. When this activity stops, the muscle fibers can relax.

The human body contains three types of muscle: skeletal, smooth, and cardiac. Skeletal muscles typically connect to bones through tendons and control voluntary actions such as walking and lifting weights. Smooth muscle lines organs and blood vessels, helping carry out automatic processes such as moving food through the digestive tract and regulating blood flow. Cardiac muscle is found only in the heart, where its contractions pump blood throughout the body.

The muscular system makes everyday activities possible, from blinking and maintaining an upright posture to performing demanding physical tasks such as running a marathon.