How does nicotine primarily function in the body?

Nicotine primarily functions in the body by first stimulating ganglia and then inhibiting them. This dual action is due to its role as a cholinergic agonist. When nicotine enters the body, it binds to nicotinic acetylcholine receptors located in the autonomic ganglia, which leads to an initial excitation or stimulation of the sympathetic and parasympathetic nervous systems. This stimulation results in various physiological responses such as increased heart rate and blood pressure.

However, with sustained exposure to nicotine, these ganglia become desensitized, resulting in a subsequent inhibition of their activity. This desensitization process can contribute to the various long-term effects of nicotine, including dependence and withdrawal symptoms.

The other options, while containing elements of truth regarding nicotine's effects and the body's response, do not accurately encompass its primary mechanism of action. For instance, adrenaline primarily stimulates the "fight or flight" response, but nicotine does not mimic adrenaline. While nicotine does affect heart rate and blood pressure, its primary action involves the stimulation and subsequent inhibition of ganglia rather than direct stimulation of the heart. Lastly, nicotine does not block dopamine receptors; instead, it actually increases dopamine levels in the brain, which is one of the reasons it can be