Final answer:
Physiological antagonists are drugs that decrease the activity of particular neurotransmitters by interfering with their synthesis or by blocking their receptors.
Step-by-step explanation:
In the context of drugs and neurotransmitters, physiological antagonists are substances that decrease the activity of particular neurotransmitters by interfering with their synthesis or by blocking their receptors. They produce an opposing effect to the endogenous ligand, which is the natural neurotransmitter.
For example, sympatholytic drugs are antagonists to the adrenergic receptors, meaning they block the ability of norepinephrine or epinephrine to bind to these receptors, reducing their activity. This results in a decrease in sympathetic function.
In summary, physiological antagonists are drugs that counteract the activity of neurotransmitters by interfering with their synthesis or blocking their receptors.