The Muscular System: Actions & Physiological Processes

Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

Did you know that the muscular system is responsible for nearly every type of movement in your body, including the movement of food to your stomach and blood to all parts of your body? Read on to learn more about this fascinating organ system.

What Is the Muscular System?

You know that your muscles help you walk to the bus and wave to your friends. But did you know that muscles are also required for other essential life processes like eating, breathing and pumping blood?

Your muscular system is responsible for nearly every form of movement in your body (the only exceptions are sperm cells and white blood cells, both of which can move on their own). This includes large, obvious movements like running and jumping, as well as more subtle ones like facial expressions, eye movements, breathing, digesting food and pumping blood. There are more than 600 muscles in your body, accounting for around 40-50% of your body weight. Muscles also play vital roles in maintaining your posture, providing balance and stability, and even keeping you warm. Who knew your muscular system was so important!

The muscular system is an organ system consisting of all the muscles in the body. As you've just learned, it's responsible for voluntary and involuntary movement, maintaining posture and balance and producing heat.

Muscles Are Made of Muscles Fibers

The muscular system is made up of specialized muscle cells or muscle fibers, called myofibers. Myo- is from the Greek word mys, meaning ''mouse'' or ''muscle''. (Apparently the Greeks thought that muscles resembled mice moving under the skin.)

Each myofiber is packed with proteins that work together to create contractions. Muscle contractions are the individual, cellular actions that produce movement in our body. These stacks of contractile proteins cause certain types of muscles to appear striped.

The stacks of proteins that allow for muscle fiber contraction create a striped pattern on certain muscle types.
Microscope image of muscle tissue.

The myofibers are organized into bundles that form muscles, the primary organs of the muscular system.

The myofibers are arranged in bundles that form muscles.
Diagram of the muscle.

Functions of the Muscular System

Muscles are attached to bones, organs and blood vessels, and are responsible for the vital tasks of movement, maintaining posture and balance, and creating body heat.

Creating Movement

Voluntary movement is movement that you are consciously aware of, like touching your toes and jumping up and down. It occurs as muscles pull on bones. Muscles are connected to bones via tendons. As the muscles contract, the tendons tug on the bones, and your joints act as levers to move your body in all directions.

Muscles work in pairs. One muscle group, such as your biceps, will contract to move your bones in one direction. That muscle group will then relax while its partner group, in our example the triceps, contracts to move your bones back in the opposite direction.

The biceps contract to move the forearm up. To move the forearm back, the biceps relax while triceps contract.
Diagram of biceps and triceps.

Involuntary movement is movement you are not consciously aware of, like digestion and breathing. This is caused by the muscles lining your organs. During the act of swallowing, for example, the muscles of the esophagus contract and relax in sequence, pushing the food down towards the stomach. Once the food is in the stomach, the muscles in the stomach wall contract and relax to mix the food with digestive chemicals.

Maintaining Posture and Balance

Your postural muscles, which are the muscles in your abdomen, back and hips, establish and maintain a proper, upright posture. These muscles act like a corset, holding your organs and upper body in place. Maintaining fit and strong postural muscles is more important for your overall health than you probably realize. It reduces back pain, supports your lungs and helps with breathing, and allows your body to stand taller and straighter.

Additionally, all muscles are constantly providing feedback to the brain regarding the position of your body and body parts. The muscles, in turn, receive signals to continually make minor adjustments, allowing you to keep your balance and posture steady. In fact, your muscles are never completely relaxed. This is referred to as muscle tone and it prevents injury to our muscles and joints and allows us to remain in a stable position even when we are asleep.

Heat Production

Our body needs to remain at a constant temperature in order to function properly. The majority of this heat, around 70-80%, is produced by our muscles. As muscles cells contract, they generate heat. This is why you get hot and sweaty when you work out. Your body takes advantage of this to help regulate its temperature. When you start to get too cold, your brain sends a signal telling your muscles to quickly contract and relax, generating heat. This is known as shivering.

You also may have noticed that you feel tired and sluggish on very hot days. This is because your brain is signaling your body to slow down, take it easy, and stop contracting those muscles. Fewer muscle contractions mean less heat production, which is important when you are getting too hot.

Muscle Types

There are three types of muscle tissue: skeletal or striated muscle, smooth muscle and cardiac muscle.

Microscope images of the three types of muscle tissue.
Microscope images of skeletal, smooth and cardiac muscle tissue.

Skeletal muscle is attached to bones and is responsible for the movement of your skeleton. This muscle type is sometimes referred to as striated muscle because of its striped appearance. ''Striation'' is simply a fancy word for ''stripes'' or ''grooves''. These muscles are under voluntary, or conscious, control.

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