Question

Identify the events occurring in muscular contractions;
(i) H-zone disappears
(ii) A band widens
(iii) I-band reduces in width
(iv) The width of A band is unaffected
(v) M line and Z line come closer
A) i, ii, v
B) i, ii, iii
C) i, iii, iv, v
D) ii, iv, v

Answer 1

Hint: Muscles are soft tissues present in the majority of species. For the contraction and relaxation of the muscle, protein filaments called actin and myosin are responsible. The role of generating force and motion is controlled by muscles.

Complete answer: In vertebrates, three types of muscles are present. They are smooth muscles, heart muscles, and skeletal muscles. The muscle fibre is made up of actin and myosin proteins that are responsible for the contraction process that side over each other. Each myofibril has alternating bands of dark and light on it. The light bands contain actins and are referred to as the I-band or isotropic band, while myosin is found in the dark band called 'A' or anisotropic band. An elastic fibre named 'Z' line is in the middle of each 'I' band, which bisects it. Firmly connected to the 'Z' line, are thin filaments. In the centre of this band, the thick filaments in the 'A' band are often held together by a thin fibrous membrane called the line. The myosin head now binds to the exposed active sites on actin in order to form a cross-bridge, using the energy from ATP hydrolysis. This pushes the actin filaments attached towards the middle of the 'A' band. The 'Z' line attached to these actions is often pushed inwards, allowing the sarcomere, i.e. contraction, to be shortened. Therefore, H-zone disappears in events occurring in muscle contraction, I-band decreases in width, A-band width is unchanged and M-line and Z-line come near.
So, option C is the correct answer.

Note: During the contraction process, both the length and shape of the cell are altered. Microfilaments are composed of actin, which belongs to the multifunctional globular protein family. During the muscle contraction process, it plays a significant role. Myosin belongs to the motor protein superfamily and is ATP dependent and responsible for actin-based motility.