(i) A voluntary muscle is a bundle of numerous striated muscle fibre..
(ii) Each fibre is long, unbranched and enclosed in a membrane called sarcolemma and its cytoplasm called sarcoplasm. Just beneath the sarcolemma in each fibre many nuclei occur, thus these fibres are multi-nucleated.
(iii) The sarcoplasm contains many myofibrils that are long, thin and unbranched.
(iv) Each myofibril consist of alternating thick 'A' and thin ‘I' band.
(v) The thick filaments lie parallel to each other while thin filaments extend between them.
(vi) At the centre of the I-band is a fine, dense dark band called Z-line. It forms a contractile unit called sarcomere.
