Muscle

Two important types of muscle are skeletal and smooth muscle. Their similarities and differences are described with regard to general morphology and ultrastructure (arrangement of filaments and t-tubules), linking structure to physiological functions. The sliding-filament theory of muscle contraction is explained. Finally, the processes by which nerves excite muscle contraction (excitation-contraction coupling) are outlined, again relating variations in these processes in the two types of muscle to differences between them in their role in the body.