What is a myofibril?

What is a myofibril?

• A. Structures that make up a muscle fiber
• B. A single muscle fiber
• C. A group of muscle fibers
• D. A nerve fiber

Answer: (A)

Myofibrils are the contractile structures inside a muscle fiber. They run the length of the muscle cell and are the components that actually produce force when a muscle contracts. Each myofibril is made up of repeating units called sarcomeres, which contain the thick (myosin) and thin (actin) filaments arranged in a way that generates shortening of the muscle when they slide past each other during contraction. This internal machinery gives a muscle fiber its striped appearance and is the primary reason the fiber can generate movement. This differs from a nerve fiber, which is part of the nervous system that sends signals to muscles to trigger contraction, not something contained inside the muscle fiber itself. It also differs from a single muscle fiber, which is the whole muscle cell, or from a group of muscle fibers, which is a fascicle. So, myofibrils are the internal, contractile elements that make up the muscle fiber.

Myofibrils are the contractile structures inside a muscle fiber. They run the length of the muscle cell and are the components that actually produce force when a muscle contracts. Each myofibril is made up of repeating units called sarcomeres, which contain the thick (myosin) and thin (actin) filaments arranged in a way that generates shortening of the muscle when they slide past each other during contraction. This internal machinery gives a muscle fiber its striped appearance and is the primary reason the fiber can generate movement.

This differs from a nerve fiber, which is part of the nervous system that sends signals to muscles to trigger contraction, not something contained inside the muscle fiber itself. It also differs from a single muscle fiber, which is the whole muscle cell, or from a group of muscle fibers, which is a fascicle. So, myofibrils are the internal, contractile elements that make up the muscle fiber.