Myofibrils

Myofibrils are the basic unit of a muscle. Muscles are composed of tubular cells called myocytes, known as muscle fibers in striated muscle, and these cells in turn contain many chains of myofibrils. They are created during a process known as myogenesis.

Myofibrils are composed of long proteins including actin, myosin, and titin, and other proteins that hold them together. These proteins are organized into a repeating unit called a sarcomere, the basic unit of muscle contraction. The arrangement of myofibrils within a fiber is such that the force generated is directed longitudinally down the fiber, pulling the ends towards the center and therefore shortening the muscle fiber.

Structure

Myofibrils are cylindrical structures, 1-2 micrometers in diameter, that run the length of a muscle fiber. They are composed of a series of sarcomeres, the basic contractile units of muscle tissue, arranged end to end. Each sarcomere is composed of long, fibrous proteins that slide past each other when the muscles contract and relax.

Function

The primary function of the myofibril is the contraction of muscle tissue. This is achieved through the sliding filament model of muscle contraction. The myofibril is composed of many sarcomeres, which contract (shorten) simultaneously, thereby contracting the entire muscle fiber, and thus the entire muscle.

Clinical significance

Abnormalities or damage to the myofibrils can lead to various muscle disorders. For example, in myopathies, the structure and function of the myofibrils are compromised leading to muscle weakness and wasting.

See also

• Muscle contraction
• Sarcomere
• Actin
• Myosin
• Titin
• Myogenesis
• Myopathies

References

Myofibrils Resources
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