Cytology and General Histology: Atlas

Muscle tissues

is typically localized in the internal organs, skin (visceral smooth muscle tissue, mesenchymal type), blood vessels (vascular smooth muscle tissue, mesenchymal type), iris of the eye (myoneural type)
smooth muscle cells are structural tissue units

Smooth muscle cells

are closely adjacent to one another. These are fusiform cells connected by intercellular gap junctions (nexuses). The cells form groups of parallel elements (bundles and/or strata)
are limited by a plasma membrane, which is covered by a basement membrane. The cells contain nuclei (in their centers) and the cytoplasm
their contractile apparatus is represented by actin and myosin filaments, though there are no sarcomere patterns, thus there is no striation either
in mesenchymal muscle tissue, few muscle cells are attached to motor nerve endings. They conduct excitation to other cells via their gap junction system
this smooth muscle tissue type is also marked by slow, involuntary tonic contractions over long periods of time though the muscle fatigue level is low
in myoneural smooth muscle tissue, any muscle cell is innervated separately to ensure a higher contraction speed