What Are Myofibrils?

Observing the fine structure of skeletal muscle under an electron microscope, myofibrils can be found that each muscle cell contains a large number of fibrous structures, which is called myofibrils (Kofliker's column) ^[1] .

Myofibril

Observing the fine structure of skeletal muscle under an electron microscope, myofibrils can be found that each muscle cell contains a large number of fibrous structures, which is called myofibrils (Kofliker's column) ^[1]

In the horizontal stripes of vertebrate skeletal muscle, neatly arranged myofibrils can be seen. The unit of myofibril of skeletal muscle is sarcomere, separated by Z membrane, with A band in the center and I band on both sides. The I band consists of I muscle filaments (mainly actin), and the A band consists of A muscle filaments (mainly myosin) and the former part of I muscle filaments. Electron microscope myofibrils are composed of many muscle microfilaments. These muscle microfilaments are regularly arranged in parallel in the myofibrils, with thick microfilaments located in the dark zone and fine filaments located in the open zone. The above band structure is very obvious in skeletal muscle, so skeletal muscle is also called striated muscle.

There is a small amount of connective tissue outside the muscle fibers called the endomysium. Many myofibers are surrounded by myofibers to form myofibers.

In addition, the myofilaments in smooth muscle are scattered, and there are no myofibrils like skeletal muscle.

Some animals have special structured myofibrils ^[4] .