Contraction is self-initiated, cells are not individually innervated. C. Smooth muscle 1. No myofibrils are present. The cytoplasm is finely fibrillar with no striations evident. Contraction is slow, sustained, and may involve only part of a cell.
Contraction can be self-initiated or by innervation.
The sliding filament theory of muscle contraction explains muscle contraction in all muscle types. Briefly, myosin and actin filaments remain constant in length but slide past one another, a process we will examine in detail. The cells contains many myofibrils aligned in parallel. Schematic diagram of a single sarcomere, showing the origin of the dark and light bands seen in the electron micrographs. The light bands are relatively isotropic in polarized light and are sometimes called I bands .