INVESTIGATIVE OPHTHALMOLOGY Fine structure of the human ciliary muscle

The ciliary muscle in human eyes consists of bundles of muscle cells surrounded by flattened connective tissue cells. Each bundle generally contains unmyelinated nerve fibers accompanied by Schwann cells and a few connective tissue components. Some of the nerve fibers contain many vesicles characteristic of nerve endings. The nerve fibers are, in a few cases, in very close apposition to the muscle cell membrane, but in most instances they are separated by basement membrane material. Single muscle cells are, in general, cylindrical and entirely wrapped in a basement membrane except at small areas of contact with other muscle cells where it is absent. The central region of these cells contains a slender nucleus, centrosomes, Golgi apparatus, endoplasmic reticulum, and abundant mitochondria. Many myofilaments oriented parallel to the length of the cell axis are found in the cytoplasm. Elongated patches of dense material are observed between the myofilaments, particularly in contact with cell membranes. Numerous pinocytic vesicles occur along the muscle cell membrane. In the spaces between the bundles, collagen, very thin collagen-like (reticular) and elastic fibers, myelinated and unmyelinated nerve fibers, and capillaries are seen. The capillary walls are thicker than those of the ciliary processes, and lack pores.