There are more than 600 muscles in the body. These muscles do everything from pumping blood to moving food through the intestines, to helping lift heavy objects (like backpacks). Some of these muscles can be controlled, and others like the heart and intestines do their jobs without having to think about it.
The main function of the muscular system is movement. Muscles are the only tissue in the body that has the ability to contract and therefore move the other parts of the body. Muscle contractions occur every time we move. The muscle must contract in order to move the bone that it is attached to or to provide resistance against a force.
The second function of the muscular system is the maintenance of posture and body position. Muscles often contract to hold the body still or in a particular position rather than to cause movement. The muscles responsible for the body’s posture have the greatest endurance of all muscles in the body—they hold up the body throughout the day without becoming tired.
Another function related to movement is the movement of substances inside the body. The cardiac and visceral muscles are primarily responsible for transporting substances like blood or food from one part of the body to another.
The final function of muscle tissue is the generation of body heat. As a result of the high metabolic rate of contracting muscle, our muscular system produces a great deal of waste heat. Many small muscle contractions within the body produce our natural body heat. When we exert ourselves more than normal, the extra muscle contractions lead to a rise in body temperature and eventually to sweating.
Muscles make up roughly half of a person’s body weight. Each muscle is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves.
There are three different kinds of muscle – visceral (smooth), cardiac, and skeletal muscle.
♣ Visceral muscle is found inside of organs like the stomach, intestines, and blood vessels. The visceral is the weakest of all muscle tissues and makes organs contract to move substances through the organ. Because visceral muscle is controlled by the unconscious part of the brain, it is known as involuntary muscle. The term “smooth muscle” is often used to describe visceral muscle because it has a very smooth, uniform appearance when viewed under a microscope.
♣ Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body. Cardiac muscle tissue cannot be controlled consciously, so it is an involuntary muscle. While hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates itself to contract. The cells of cardiac muscle tissue are striated—that is, they appear to have light and dark stripes when viewed under a light microscope. The arrangement of protein fibers inside of the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles.
♣ Skeletal muscle is the only voluntary muscle tissue in the human body—it is controlled consciously. Every physical action that a person consciously performs (e.g. speaking, walking, or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts of the body closer to the bone that the muscle is attached to. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other. Most skeletal muscles are attached to two bones through tendons which are tough bands of dense regular connective tissue whose strong collagen fibers firmly attach muscles to bones. Tendons are under extreme stress when muscles pull on them, so they are very strong and are woven into the coverings of both muscles and bones. Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other.
The muscles of the head and neck are responsible for movement of the head and neck, chewing and swallowing, speech, facial expressions, and movement of the eyes. These diverse tasks require both strong, forceful movements and some of the fastest, finest, and most delicate adjustments in the entire human body. The muscles of the face are unique in that while most muscles connect to and move only bones, facial muscles mostly connect bones to skin.
The muscles of the chest and upper back control many motions that involve moving the arms and head – such as throwing a ball, looking up at the sky, and raising your hand. Breathing, a vital body function, is also controlled by the muscles connected to the ribs of the chest and upper back.
The muscles of the abdomen, lower back, and pelvis are separated from those of the chest by the muscular wall of the diaphragm (the critical breathing muscle) and play a critical role in protecting the delicate vital organs within the abdominal cavity. These muscles also function in movement of the trunk, posture, and stability of the entire body.
The muscles of the arm and hand are specifically designed to meet the body’s diverse needs of strength, speed, and precision while completing many complex daily activities such as lifting weights or heavy boxes which require brute strength from the muscles of the arm. Writing, painting, and typing all require speed and precision from the same muscles. Complete athletic activities such as boxing or throwing a ball require arm and hand muscles to be strong, fast, and precise all at the same time. The muscles of the upper arm are responsible for the flexion and extension of the forearm at the elbow joint.
The muscles of the legs and feet support, balance and propel the body. From the large, strong muscles of the buttocks and legs to the tiny, fine muscles of the feet and toes, these muscles can exert tremendous power while constantly making small adjustments for balance. The powerful muscles of the hip, buttock, and pelvis actuate the flexible ball-and-socket hip joint. The muscles of the calf work to stabilize the ankle joint and foot and to maintain the body’s balance.