Muscle Fiber Structure and Striations — NEET Biology
✅ Asked in NEET 2023Muscle fibre is a syncitium as the sarcoplasm contains many nuclei. The endoplasmic reticulum, i.e., sarcoplasmic reticulum of the muscle fibres is the store house of calcium ions. A characteristic feature of the muscle fibre is the presence of a large number of parallely arranged filaments in the sarcoplasm called myofilaments or myofibrils. Each myofibril has alternate dark and light bands on it. A detailed study of the myofibril has established that the striated appearance is due to the distribution pattern of two important proteins – Actin and Myosin. The light bands contain actin and is called I-band or Isotropic band, whereas the dark band called 'A' or Anisotropic band contains
NTA tests your understanding that muscle fibers are syncytia (multinucleated) with sarcoplasm containing calcium-storing sarcoplasmic reticulum, and that striations result from alternating actin (I-bands/light) and myosin (A-bands/dark) proteins. Students commonly confuse which protein is in which band—remember I-band = Isotropic = actin (lighter), A-band = Anisotropic = myosin (darker). Another trap: students forget that sarcoplasm isn't just cytoplasm but specifically the muscle cell's cytoplasm, and the sarcoplasmic reticulum's calcium role is critical for muscle contraction. This concept appears frequently because understanding sarcomere structure is fundamental to explaining the sliding filament mechanism tested in every NEET exam.
Which of the following statements are correct regarding skeletal muscle? A. Muscle bundles are held together by collagenous connective tissue layer called fascicle. B. Sarcoplasmic reticulum of muscle fibre is a store house of calcium ions. C. Striated appearance of skeletal muscle fibre is due to distribution pattern of actin and myosin proteins. D. M line is considered as functional unit of contraction called sarcomere. Choose the most appropriate answer from the options given below:
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