Muscle Types


Cardiac muscle tissue occurs only in the heart. Its cells are joined from one end to the other. Each cell has a single nucleus. At its end, there is an intercalated disc. Unlike skeletal muscle, cardiac muscle is controlled involuntarily.


Smooth muscle tissue is located in the walls of hollow internal structures, such as blood vessels. Similar to cardiac muscle, smooth muscle fibers are mostly involuntary, and they are nonstriated. Smooth muscle tissue, like skeletal and cardiac muscle tissue, can grow in size or hypertrophy.


Skeletal muscle is, as the name suggests, attached to bones. It is striated, (not smooth) and can contract or relax voluntarily. Each muscle is composed of single fibers embedded in a matrix of collagen. At either end of the muscle belly, this matrix becomes the tendon that connects the muscle to bone.  There are three types of skeletal muscle fibers.

Type I Fibers

Also called slow twitch muscles, Type I fibers are red and split Adenosine Triphosphate at a slow rate.

Type II A Fibers

Also called fast twitch muscles, Type II A fibers are red and have a very high capacity for generating ATP. Rare in humans, Type II muscle fibers have a fast contraction velocity and are resistant to fatigue.

Type II B Fibers

Type II B fibers are also called fast twitch, but these fibers are white and fatigue easily. These fibers are found in large numbers in the muscles of the arms and legs.

Leave a Reply