Question

Sarcomere extends between

• A. Two I-bands
• B. A and I bands
• C. Two Z-lines
• D. Z and A bands

Answer 1

The correct option is C Two Z-lines

• Each myofibril(a unit of the muscle cell) has alternate dark and light bands on it.
  
• The light bands contain actin and are called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin.
  
• In the center of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line.
  
• The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils.
  
• The sarcomere is considered as the functional unit of contraction. The portion of the myofibril between two successive ‘Z’ lines is considered as a sarcomere. Hence sarcomere is the distance between two Z lines.
• So, the correct answer is 'Two Z-lines'.