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.
One neurotrans-mitter used by many neuronsthroughout the brain is serotonin,also known as 5-hydroxytryptamine(5-HT). Serotonin released by thesignal-emitting neuron subtly altersthe function of the signal-receivingneurons in a process called neuro-modulation. For example, in someneurons serotonin alters the rate ...