the disk in the fundus of the eye marking the point at which the optic nerve enters; it is accompanied by blood vessels, is oval, light in color and the blind spot of the retina.
ARTERIOLES. In arterioles, the tunica intima consists of a continuous endothelium and a very thin subendothelial layer. In addition, a thin, fenestrated internal elastic lamina is present in larger arterioles but absent in terminal arterioles. Generally, the tunica media consists of 2 layers of smooth muscle cells.
SMOOTH MUSCLE - STRUCTURE. Smooth muscle (shown below) is made up of fusiform (diamond-shaped) cells with a single nucleus. The cells are arranged in sheets and contain three filament types: a) actin filaments with no troponin and tropomyosin (5 - 8 times more actin than skeletal muscle).