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.
In response to a stimulus, the brain or the spinal cord may initiate muscle cell contraction to enable movement. The neurotransmitter that signals muscle cell contraction is acetylcholine, and it is released in the synapse between the neuron and the muscle cell. If the acetylcholine that is released is not broken down, the muscle cells remain in a contracted state and cannot respond effectively to new signals from the brain.