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.
Sarcomere contains two main types of protein fibers: Myosin-the thicker filament and Actin â the thinner filament. When activated, the contraction is produced by sliding of the myosin fibers over the actin fibers in each sarcomere, which in turn produces a contraction of the muscle cell.