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.
Now that we have described the structure of the neuromuscular junction, we are ready to examine what happens there. When the nerve impulse reaches the axon terminals, a chemical referred to as a neurotransmitter is released. The specific neurotransmitter that stimulates skeletal muscle cells is acetylcholine, or Ach. Acetylcholine diffuses across the synaptic cleft and attaches to receptors (membrane proteins) that are part of the sarcolemma. If enough acetylcholine is released, the sarcolemma at that point becomes temporarily more permeable to sodium ions (Na+), which rush into the muscle cell and to potassium ions (K +) which