Skeletal Muscle

What is skeletal muscle?

The majority of the muscles in your body are skeletal muscles (striated muscles). They make up between 30% and 40% of your total body mass. Tendons (tough bands of connective tissue) attach skeletal muscle tissue to bones throughout your body. Your shoulder muscles, hamstring muscles and abdominal muscles are all examples of skeletal muscles.

There are three types of muscles in your body: skeletal, cardiac and smooth muscle. Skeletal muscles are voluntary muscles, meaning you control how and when they move and work. Nerves in your somatic nervous system send signals to make them function. If you reach for a book on a shelf, you’re using skeletal muscles in your neck, arm and shoulder.

Cardiac and smooth muscle are involuntary muscles that your autonomic nervous system controls. That means they work without you having to think about it. For example, muscles in your urinary system help rid your body of waste and toxins.

Skeletal muscle mass varies from person to person. Males have more skeletal muscle mass than females. People who are tall or have overweight also tend to have higher muscle mass. Muscle mass decreases with age.

What do skeletal muscles do?

Your striated muscles are a vital part of your musculoskeletal system. They serve a variety of functions, including:

• Chewing and swallowing, which are the first parts of digestion
• Expanding and contracting your chest cavity so you can inhale and exhale
• Maintaining body posture
• Moving the bones in different parts of your body
• Protecting your joints and holding them in place
• Storing nutrients
• Sustaining body temperature

Where are the skeletal muscles located?

Your skeletal muscles are located between the bones (skeletal system) throughout your body. They consist of flexible muscle fibers that range from less than half an inch to just over 3 inches in diameter. These fibers usually span the length of the muscle. The fibers contract (tighten), which allows the muscles to move bones so you can perform lots of different movements.

What are the parts of skeletal muscles?

Each muscle can contain thousands of fibers. Different types of sheaths, or coverings, surround the fibers:

• Epimysium. The outermost layer of tissue surrounding the entire muscle.
• Perimysium. The middle layer surrounding bundles of muscle fibers.
• Endomysium. The innermost layer surrounding individual muscle fibers.

What do skeletal muscles look like?

Skeletal muscle fibers are red and white. They look striated, or striped, so they’re often called striated muscles. Cardiac muscles are also striated, but smooth muscles aren’t.

What are the common conditions and disorders that affect striated muscles?

A wide range of conditions can affect skeletal muscles, from mild injuries to serious or even life-threatening myopathies (diseases that affect skeletal muscles). A few are:

• Muscular dystrophies
• Myasthenia gravis (MG)
• Rhabdomyolysis
• Sarcopenia
• Strains
• Tendonitis