The cholinergic and adrenergic nerve innervation and nerve endings of the iris muscle in Cynomolgus monkey eye is studied by electron microscopy.
In the iris, the sphincter muscle reveals nerve terminals containing small empty vesicle which is said to be cholinergic in a greater number (about 85% of nerve terminals) and those containing small cored vericles which is said to be adrenergic in a fewer number (about 15% of nerve terminals) and the latter are more frequently found in the region of peripheral one third of the sphincter muscle then the rest two thirds. In the dilator muscle 65% of the nerve terminals is found to be adrenergic and 35% cholinergic.
A dual innervation, adrenergic and cholinergic nerves in both the iris dilator and the sphincter muscle, is not clearly explained in their functions, that is, how influence two nerves one another in addition to the effector cells.
A single or double layer of basement membrane lies between the nerve terminals and adjacent muscle in the stromal site of iris muscle. In part the close apposition of the nerve with muscle membrane is seperated by an intercellular space of about 200 A, which is much more in the muscle bundles than in the peripheral portion of the sphincter muscle, however a few in the dilator muscle.
The two or three adrenergic and cholinergic axons or terminals in the iris muscle are often closely adjacent to one another, which nerve terminals are not clarified, whether two nerves is motor, or afferent and efferent nerve unit.
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