什么是 Muscle tissue？

Muscle tissue is made of elongated cells packed with contractile protein filaments (actin and myosin). Three kinds: skeletal muscle, of long multinucleate fibres showing cross-striations, attached to the skeleton and under voluntary control; cardiac muscle, of branched striated cells joined end to end by junctions that pass the beat from cell to cell, contracting on its own rhythm; smooth muscle, of spindle-shaped unstriated cells in the walls of hollow organs (gut, vessels, uterus), contracting slowly and involuntarily. The mechanism of contraction is treated in the Year 2 volume.