CBSE Class 11-science Answered

Structure of Myofibril:

The myofibril is a unit filament of a muscle fibre.

It is made of two kinds of bands - dark band and light band.

A dark band is also known as an A or anisotropic band (myosin filament) and contains myosin, while the light band is also known as an I or isotropic band (actin filament) and contains actin.

Both the bands or filaments are arranged parallel to each other.

Actin filaments are thinner than myosin filaments and are hence also called thin and thick filaments, respectively.

At the centre of each I band is an elastic fibre called Z-line to which thin filaments are firmly attached.

The thick filaments in the A band are held together by an M line.

The portion of the myofibril between two successive Z lines is considered functional and is called a sarcomere.

In the resting state, the edges of thin filaments partially overlap the free ends of thick filaments on either side leaving the central parts of the thick filament non-overlapped; this is called the H zone.