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Q.
In a muscle, the functional unit of contraction is the ………. portion of myofibril between two successive ‘Z’lines.
Locomotion and Movement
Solution:
Each muscle fibre contains many myofibrils that have characteristic striations (stripes).A myofibril has dark and light bands. The dark bands are also called Abands (anisotropic bands). The light bands are also called I- bands (isotropic bands). At the centre of A-band, a comparatively less dark zone called H-zone (Hensen zone) is present. In the centre of the Hzone is the M-line. Each I-band has at its centre a dark membrane called Z-line. It is also called Z-disc, or Krause’s membrane or Dobie’s line. The part of the myofibril between two successive Z-lines is called sarcomere which is the functional unitofmyofibril. Thesarcomere comprises A-band and half of each adjacent I-band. Each sarcomere is a bundle of thick and thin myofilaments. During muscle contraction, whereas thin myofilaments slide over thick myofilaments. The length of the sarcomere decreases during contraction, lengths of the thick and thin myofilaments do not change during contraction.