Smooth muscle in human intracerebral arterioles.

Aterioles from the human cerebral cortex have been examined by electron microscopy in several patients aged 43 to 58 years. The wall of all arterioles (ranging in size from 10-70 microns in diameter) is composed of a single layer of endothelium and from one to 5 layers of smooth muscle cells. A basal lamina supports the endothelium and encloses the smooth muscle cells. Smooth muscle cells were identified by morphological criteria that included the presence of dense bodies, abundant microfilaments and numerous pinocytotic vesicles. Some of the intracerebral arterioles were observed in a constricted state indicating functional smooth muscle cells. The presence of functional smooth muscle cells in human intracerebral arterioles indicates that these arterioles are capable of vasoconstriction which may be a possible factor in some clinical conditions.