In
physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
, isotropic bands (better known as
I bands
I, or i, is the ninth letter and the third vowel letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''i'' (pronounced ), plural ...
) are the lighter bands of skeletal muscle cells (a.k.a.
muscle fibers
A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...
). Isotropic bands contain only
actin
Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over ...
-containing
thin filaments
Myofilaments are the three protein filaments of myofibrils in muscle cells. The main proteins involved are myosin, actin, and titin. Myosin and actin are the ''contractile proteins'' and titin is an elastic protein. The myofilaments act together ...
.
The darker bands are called anisotropic bands (
A bands). Together the I-bands and A-bands contribute to the striated appearance of
skeletal muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
.
Isotropic bands indicate the behavior of polarized light as it passes through I bands.
Diagrams provide an indication of what I and A Bands look like, through a microscope.
References
Muscular system
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