Myofibrils

Definition

Myofibrils are long, thread-like structures found in muscle cells that are essential for muscle contraction. They are composed of repeating units called sarcomeres, which contain the proteins actin and myosin.

5 Must Know Facts For Your Next Test

1. Myofibrils make up the bulk of the cytoplasm in muscle fibers.
2. Sarcomeres within myofibrils are responsible for the striated appearance of skeletal and cardiac muscles.
3. The sliding filament theory explains how myofibrils contract through the interaction of actin and myosin filaments.
4. Myofibrils are surrounded by the sarcoplasmic reticulum, which stores calcium ions necessary for muscle contraction.
5. Damage to myofibrils can lead to muscle weakness and diseases such as muscular dystrophy.

Review Questions

• What structural components make up a myofibril?
• How do myofibrils contribute to the striated appearance of certain muscle types?
• What role does calcium play in the function of myofibrils?

Related terms

Sarcomere: The basic functional unit of a myofibril responsible for muscle contraction.

Actin: A protein filament involved in muscle contraction and is a major component of sarcomeres.

Sarcoplasmic Reticulum: An organelle that surrounds myofibrils and regulates calcium ion concentration.