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Distinguish between preganglionic and postganglionic neurons.
Preganglionic fibers come from the preganglionic neurons that reside in the CNS. These fibers synapse with the cell body of the postganglionic neurons, which lie in ganglia. Postganglionic fibers come from the postganglionic neurons and innervate the target organ.
What is the advantage of dual innervation of an organ by both branches of the autonomic nervous system?
Since the two systems most often produce opposite actions on a target organ, dual innervation enables precise control over an organ's activity.
Compare agonists and antagonists.
Agonists bind to the neurotransmitter's receptor and mimic the neurotransmitter by causing a similar response as would the neurotransmitter. Antagonists bind the neurotransmitter receptor, but have no stimulatory action, therefore blocking the neurotransmitter from binding to the receptor and preventing activation of the receptor.
Describe the sequence of events that occurs at a neuromuscular junction.
Action potential occurs in the motor neuron; Ca2+ enters motor neuron; axon terminal triggers release of acetylcholine; acetylcholine binds to receptors on the motor end plate; Na channels open/Na enters the cell and K+ channels open/K+ leaves the cell, creating a depolarizing end plate potential; local depolarizing current flow continues and opens voltage-gated Na channels in adjacent membrane; cell reaches threshold and initiates an action potential. Acetylcholine is subsequently destroyed by acetylcholinesterase, an enzyme located on the motor end plate.
Discuss the effect each of the following has at the neuromuscular junction: black widow spider venom, botulinum toxin, and myasthenia gravis.
Black widow spider venom causes excess release of acetylcholine, causes excess depolarization, paralysis occurs. Botulinum toxin blocks release of acetylcholine, neurons cannot release enough acetylcholine, paralysis occurs. Myasthenia gravis is an autoimmune disease in which acetylcholine receptors are progressively destroyed by erroneously acting antibodies, muscles cannot respond to acetylcholine, paralysis occurs.
