An agonist is a chemical that does what?

• A. Blocks action from the neuron
• B. Facilitates and mimics the effect of a neurotransmitter
• C. Breaks down neurotransmitters
• D. Binds irreversibly to receptors only

Answer: (B)

An agonist activates receptors to produce a response, mimicking the action of a natural neurotransmitter. When it binds to a receptor, it turns on the same signaling pathway the neurotransmitter would, facilitating the neuron's activity or the downstream effect in the target cell. This is why an agonist is described as facilitating and mimicking the neurotransmitter’s effect.

In contrast, blocking signaling from a neuron comes from antagonists, which prevent the receptor from being activated. Breaking down neurotransmitters is done by enzymes that terminate signaling, not by activating receptors. Some ligands can bind irreversibly to receptors, but that characteristic doesn’t define an agonist; agonists can be either reversible or irreversible while still activating the receptor.