NEET BIOLOGY

Detailed explanation-1: -There are two types of myofilaments . Thin actin filament and thick myosin filament. Both the filaments are arranged alternately. The region where both myofilaments are present is seen as dark and is called as dark band.

Detailed explanation-2: -Isotropic bands contain only actin-containing thin filaments. The darker bands are called anisotropic bands (A bands).

Detailed explanation-3: -The dark bands are the striations seen with the light microscope. When a muscle contracts the light I bands disappear and the dark A bands move closer together. This is due to the sliding of the myofilaments against one another. The Z-lines pull together and the sarcomere shortens as above.

Detailed explanation-4: -Hint: The muscle fibres contain parallelly arranged myofibrils which have alternate light and dark bands. The dark present on the myofibril is called ‘A-band’ or anisotropic band and the light band present on the myofibril is called I-band or isotropic band.

Detailed explanation-5: -The dark band is known as ‘A’ or Anisotropic band which carries Myosin whereas the light bands which carry actin and are called I-band or Isotropic band which results in striations and hence striped appearance.