Final answer:
An antagonist is a drug that binds to a cell's receptor site, blocking or reducing the typical response by interfering with neurotransmitter activity. These drugs are used to modulate responses in conditions like Parkinson's disease where neurotransmitter imbalances are present. Alpha and beta-adrenergic receptors can be targeted by these antagonists in the autonomic nervous system.
Step-by-step explanation:
The type of drug that binds with a receptor site on a cell and either blocks or precipitates a less than typical response is called an antagonist. Antagonists work by blocking or impeding the normal activity of a neurotransmitter at the receptor, which in turn decreases the activity of particular neurotransmitters. These may act by interfering with neurotransmitter synthesis, or by occupying the receptor so that the actual neurotransmitter cannot bind. On the other hand, agonists are drugs that mimic the effect of the neurotransmitter at the receptor site, often prescribed to correct specific neurotransmitter imbalances, such as dopamine agonists used in the treatment of Parkinson's disease.
An example of the antagonist effect can be seen with drugs that block alpha (α)-adrenergic or beta (β)-adrenergic receptors, which are related to the autonomic nervous system's response. Antagonists can also be molecules that bind to and block other types of receptors, including ion channel-linked receptors. Testosterone, which is a steroid hormone, would have its effect diminished by an antagonist that blocks plasma membrane receptors by preventing its ability to exert biological effects.