Question
Excitatory neurotransmitters like acetylcholine Select one: a. increase the permeability of postsynaptic membranes to sodium. b. block the postsynaptic membrane's receptor sites. c. decrease the permeability of postsynaptic membranes to sodium. d.hyperpolarize a postsynaptic neural membrane.
Solution
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Jorge
Veteran ยท Tutor for 10 years
Answer
The correct answer is **a. increase the permeability of postsynaptic membranes to sodium.**Here's why:Excitatory neurotransmitters increase the likelihood of the postsynaptic neuron firing an action potential. They do this by depolarizing the postsynaptic membrane. Acetylcholine, a common excitatory neurotransmitter, binds to receptors on the postsynaptic membrane, causing sodium channels to open. The influx of positively charged sodium ions into the cell depolarizes the membrane, making it more positive and bringing it closer to the threshold potential required for an action potential.Let's look at why the other options are incorrect:* **b. block the postsynaptic membrane's receptor sites:** This describes the action of *antagonists*, which *inhibit* neurotransmission, not excitatory neurotransmitters.* **c. decrease the permeability of postsynaptic membranes to sodium:** This would make it *harder* for the postsynaptic neuron to fire, which is the opposite of what excitatory neurotransmitters do.* **d. hyperpolarize a postsynaptic neural membrane:** Hyperpolarization makes the membrane potential more negative, moving it *further* away from the threshold for an action potential. This is characteristic of *inhibitory* neurotransmitters, not excitatory ones.