AAMC FL Practice Exam

How does an antagonist function in relation to receptors?

1. It strengthens the receptor's response

2. It binds without producing a biological effect

3. It inhibits the response triggered by the receptor

4. It activates the receptor to cause a response

The correct answer is: It inhibits the response triggered by the receptor

An antagonist functions primarily by inhibiting the response triggered by a receptor. When an antagonist binds to a receptor, it occupies the binding site but does not activate the receptor, which prevents the natural ligand (such as a hormone or neurotransmitter) from exerting its effect. This blockage halts any downstream signaling pathways that would normally be activated by the receptor when it is engaged by its typical ligand. For example, in the context of neurotransmission, if an antagonist binds to a receptor in the presence of a neurotransmitter, it can prevent the neurotransmitter from initiating its usual effects, such as muscle contraction or neuronal excitation. Thus, the overall action of an antagonist is to reduce or completely inhibit the biological response that would normally occur when the receptor is activated.