A cataract is a clouding of the lens in the eye that affects vision. Most cataracts are related to aging. Cataracts are very common in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery.
Acetylcholine. Acetylcholine (ACh) is the transmitter released by the preganglionic nerve terminals of both the sympathetic and the parasympathetic divisions (Fig 6.2). The synapse at those sites utilizes a nicotinic receptor similar in structure to the receptor at the neuromuscular junction.
Unlike skeletal muscle, there is no specialized connection between the nerve fiber and the smooth muscle cell. The nerve fibers essentially passes close to the smooth muscle cells and releases the neurotransmitter (which is not restricted to acetylcholine-see below) from swellings in the fiber, called varicosities.