Table 1.
Comparison of the properties of the three types of mammalian muscle
| Characteristic | Skeletal muscle | Cardiac muscle | Smooth muscle |
|---|---|---|---|
| Striation | Yes | Yes | No |
| Number of nuclei/cell | Many | 1, 2, or 3 | 1 |
| Innervation | Somatic | ANS | ANS |
| T-tubules | Yes | Yes | No |
| SR | +++ | ++ | + to ++ |
| Regulatin of actin–myosin interaction | Ca2+ binding to Tn | Ca2+ binding to Tn | Myosin (RLC) phosphorylation (Ca2+–CaM-mediated) |
| Sources of activator Ca2+ | SR | SR and ECF | SR and ECF |
| Site of Ca2+ action | Tn C | Tn C | MLCK |
| Speed of contraction | Slow to fast | Slow | Very slow |
| Inherent tone—low levels of maintained tension | No | No | Yes |
| Physiological pacemaker potentials | No | Yes | Yes (phasic) |
| Effects of nervous stimulation | Excitation | Excitation and inhibition | Excitation and inhibition |
ANS, autonomic nervous system; CaM, calmodulin; ECF, extracellular fluid; RLC, regulatory light chain; Tn, troponin; MLCK, myosin light-chain kinase; SR, sarcoplasmic reticulum.