ANATOMY

Detailed explanation-1: -The area between two Z lines, a sarcomere, can be considered to be the primary structural and functional unit directly responsible for muscle contraction. The myofibril can thus be thought of as a stack of sarcomeres. The A band, which contains thick filaments partly overlapped with thin filaments, appears dark.

Detailed explanation-2: -The arrangement of the thick myosin filaments across the myofibrils and the cell causes them to refract light and produce a dark band known as the A Band. In between the A bands is a light area where there are no thick myofilaments, only thin actin filaments. These are called the I Bands.

Detailed explanation-3: -The myosin filaments are called thick filament. The thick filaments in the ‘A’ band are also held together in the middle of this band by a thin fibrous membrane called ‘M’ line. The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.

Detailed explanation-4: -The myofibrils are made up of thick and thin myofilaments, which give the muscle its striped appearance. The thick filaments are composed strands of the protein myosin, and the thin filaments are strands of the protein actin, along with two other muscle regulatory proteins, tropomyosin and troponin.

Detailed explanation-5: -Each sarcomere consists of a central A-band (thick filaments) and two halves of the I-band (thin filaments). The I-band from two adjacent sarcomeres meets at the Z-line. The central portion of the A-band is the M-line, which does not contain actin.