(a) A voluntary muscle is a bundle of numerous striated muscle fibre.
(b) Each fibre is long, unbranched and enclosed in a membrane called sarcolemma and its cytoplasm called sarcoplasm.
(c) The sarcoplasm contains many myofibrils that are long, thin and unbranched.
(d) Each myofibril consist of alternating thick A and thin I band.
(e) The thick filaments lie parallel to each other while thin filaments extend between them.
(f) At the centre of the I-band is a fine, dense dark
band called Z-line. It forms a contractile unit called sarcomere.