Difference between A-Band and I-Band of Sarcomere – Comparison Tab


A-band vs I-band

A-Band vs I-Band
Difference between A-Band and I-Band of a Sarcomere

The basic structural and functional unit of a striated muscle is called the Sarcomere. The sarcomere is the repeating units of a striated muscle occur between two Z-lines. This gives the striated appearance of the skeletal or cardiac muscles. The sarcomere composed of myofibrils, an array elongated contractile protein threads found in striated muscle cells. There are two types of myofibrils in the sarcomere called thin filaments and thick filaments. The thin filaments are made of protein called Actin and the thick filaments are made of proteins called Myosin. The actin and myosin filaments in a sarcomere are arranged in a specific manner so that their overlapping and interlocking patterns produce distinct bands when they are observed under a microscope. These bands are technically called as A-bands (Anisotropic) and I-Bands (Isotropic). The present post discusses the Difference between A-bands and I-bands with a comparison table.

Sarcomere diagram

Structure of Sarcomere (Source: Wikipedia)

Difference between A-Band and I-Band

Sl. No.A-BandI-Band
1A-Bands are the anisotropic bands of the sarcomere.I-Bands are the isotropic bands of sarcomere.
2A-Band appears as dark bands under the microscope.I-Band appears as light bands under the microscope.
3A-Band has a wide light zone called H zone (Henson’s zone) in the middle.I-Band has a ‘Cross’ at its middle portion by a thick dark membrane called Z-line.
4A-Band contains primary myofilaments and parts of secondary myofilaments.I-Bands contain parts of secondary myofilaments only.
5Length of A-Band remains unchanged during the muscle contraction.I-Band shortens during muscle contraction.

Structure of Sarcomere

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