A skeletal muscle consists of a bundle of long fibres running the length of the muscle. Each fibre is a single cell with many nuclei.

Skeletal muscle is also called striated muscle because of the regular arrangement of the and dark bands. Each repeating pattern of light and dark bands. 

Each repeating unit is a sarcomere, the basic functional unit of the muscle. The borders of the sarcomere, the Z-lines are lined up in adjacent myofibrils and contribute to the striations visible with a light microscope. The thin filaments are attached to the Z-lines and project towards the centre of the sarcomere while the thick filaments are centred in the sarcomere. At rest, the thick and thin filaments do not overlap completely, and the area near the edge of the sarcomere where there are only thin filaments is called the I -band. 

The A-band is the broad region that corresponds to the length of the thick filaments. The thin filaments do not extend completely across the sarcomere. So, the H-zone in the centre of the A-band contains only thick filaments. This arrangement of thick and thin filaments is the key to how the sarcomere and hence, the whole muscle contracts.