I band

I Band

The I band (also known as the isotropic band) is a band within the sarcomere, the basic unit of a muscle's contractile apparatus. The I band is one of the many components that contribute to muscle contraction and is unique in its composition and function.

Structure

The I band is a region of the sarcomere that is made up of thin filaments, primarily actin. It is flanked by two A bands and bisected by the Z line. The I band is the only region of the sarcomere that does not contain thick myosin filaments, which gives it its characteristic light appearance under polarized light microscopy, hence the term "isotropic".

Function

The primary function of the I band is to facilitate muscle contraction. During contraction, the I band shortens as the actin filaments slide over the myosin filaments in the A band, a process known as the sliding filament theory. This results in the overall shortening of the sarcomere and thus, muscle contraction.

Clinical significance

Abnormalities in the I band can lead to various muscular disorders. For instance, mutations in the genes encoding for actin can disrupt the structure and function of the I band, leading to conditions such as actin myopathy and nemaline myopathy.

See also

• A band
• Z line
• H zone
• M line
• Sarcomere
• Muscle contraction
• Sliding filament theory