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Muscular System: Facts, Functions & Diseases

The 650 muscles in the human body control movement and help to maintain posture, circulate blood and move substances throughout the body.

While most people associate muscles with strength, they do more than assist in lifting heavy objects. The 650 muscles in the body not only support movement — controlling walking, talking, sitting, standing, eating and other daily functions that we consciously perform — but also help to maintain posture and circulate blood and other substances throughout the body, among other functions.

Description of the muscular system

The nervous system controls the actions of the muscles, although some muscles, including the cardiac muscle, can function autonomously. Muscles make up more than half of the weight of the human body, and people who do heavy weight training often gain weight because muscle is about three times as dense as fat.

The muscular system can be broken down into three types of muscles: skeletal, smooth and cardiac.

Skeletal muscles are the only voluntary muscle tissue in the human body and control every action that a person consciously performs. 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.

Visceral, or smooth, muscle is found inside of organs such as the stomach, intestines, and blood vessels. It is called a smooth muscle because unlike skeletal muscle, it does not have the banded appearance of skeletal or cardiac muscle. The weakest of all muscle tissues, visceral muscles send signals to 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 as it cannot be controlled by the conscious mind.

Found only in the heart, cardiac muscle is responsible for pumping blood throughout the body. The heart’s natural pacemaker is made of cardiac muscle that signals other cardiac muscles to contract. Like visceral muscles, cardiac muscle tissue is controlled involuntarily. While hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates itself to contract.

Muscles are further classified by their shape, size and direction. The deltoids have a triangular shape. The serratus muscle, which originates on the surface of the second to ninth ribs at the side of the chest and runs along the entire anterior length of the scapula, has a distinguishing saw-like shape. The rhomboid major is a diamond shape.

Size can be used to differentiate similar muscles in the same region. The gluteal region contains three muscles differentiated by size — the gluteus maximus (large), gluteus medius (medium), and gluteus minimus (smallest).

The direction in which the muscle fibers run can be used to identify a muscle. In the abdominal region, there are several sets of wide, flat muscles. The muscles whose fibers run straight up and down are the rectus abdominis, the ones running transversely (left to right) are the transverse abdominis, and the ones running at an angle are the obliques. As any exercise enthusiast knows, obliques are among the hardest muscles to develop and achieve “six-pack” abs.

Muscles can also be identified by their function. The flexor group of the forearm flexes the wrist and the fingers. The supinator is a muscle that supinates the wrist by rolling it over to face palm up. Abductor muscles in the legs adduct, or pull together, the limbs.

Diseases of the muscular system

There is no one type of doctor that treats muscular diseases and disorders. Rheumatologists, orthopedists, and neurologists may all treat conditions which affect the muscles.

Because the muscular system impacts so many of the functions necessary to sustain life, any disease or disorder can cause health problems, ranging from minor to severe. Not only do muscular disorders affect mobility, but can result in many other functional abnormalities, such as the inability to breath, swallow or speak.

Muscular dystrophy is a genetic disease that damages muscle fibers. The symptoms of muscular dystrophy disease include weakness, loss of mobility and lack of coordination. More than 50,000 Americans suffer with one of the nine forms of the disease, which can occur at any time in a person’s life and has no cure.

Cerebral palsy impacts posture, balance and motor functions. Brain damage during or before childbirth causes a loss of muscle tone, making it difficult to perform everyday tasks. It is one of the most common congenital disorders.

Myasthenia gravis is a chronic autoimmune disease that results in muscle weakness and fatigue. A breakdown of the neuromuscular junction causes the brain to lose control over these muscles, which can result in difficulty breathing and swallowing,

Amyotrophic lateral sclerosis (ALS), often referred to as "Lou Gehrig's disease," is a progressive neurodegenerative disease that affects nerve cells in the brain. It is a fatal disease that affects 30,000 Americans at any one time and leads to a loss of control over voluntary muscle movement, making it increasingly difficult to swallow, breath and speak. The disease ultimately causes paralysis and death.

Fibromyalgia is a chronic disorder characterized by widespread muscle pain, stiffness, fatigue, and tenderness in localized areas. While this is a difficult disease to pinpoint and diagnose and can mimic many other medical problems, it has gained acceptance as a recognized health issue over the past decade.

Infographic: How the human body's muscles work.

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Ready for Med School? Test Your Body Smarts
You use your eyes to see, your ears to hear and your muscles to do the heavy lifting. Well, sort of. In fact, most body parts are far more complicated than that, while some seem to have no business being inside there at all.
Find out how much you know about the body's parts and what they do (or don't do).
Start the Quiz
An illustration showing the different systems of the human body.
0 of 10 questions complete
Ready for Med School? Test Your Body Smarts
You use your eyes to see, your ears to hear and your muscles to do the heavy lifting. Well, sort of. In fact, most body parts are far more complicated than that, while some seem to have no business being inside there at all.
Find out how much you know about the body's parts and what they do (or don't do).
Start Quiz
An illustration showing the different systems of the human body.
0 of questions complete

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