Smooth Muscle-Artery

This figure shows a cross-section through the smooth muscle cells of the tunica me dia (vascular coat) of the parotid gland. The cell at the top center underneath the endothelium 1 contains a nucleus 2 . In addition, there are small groups of ribosomes, a few crista-type mitochondria and groups or rows of vesicles, called caveolae , and pre dominantly located along the sarcolemma, small dense areas (dense spots ) , which serve as focal adhesion points for contractile fibers. The myofilaments in this figure are cut across their long axis, and therefore appear as small spots in the cytoplasm. Nexuses  (contacts) are present in a few places between neighboring muscle cells .  They are loci with low electrical resistance and serve as excitation conduits.  Note that a basal membrane envelops the muscle cells. The extracellular collagen fibrils have been pre dominantly cut across their axis .

1 Endothelium

2 Nucleus

3 Extracellular connective tissue space with collagen fibrils

4 Fibrocyte

Electron microscopy; magnification: × 9500

References

Kuehnel, W.(2003). Color Atlas of Cytology, Histology, and Microscopic Anatomy. 4^th edition . Institute of Anatomy Universitätzu Luebeck Luebeck, Germany . Thieme Stuttgart · New York .