Nicotine from cigarette smoke acts as a ligand and associates with the acetylcholine receptor on specific cells in the nervous system. Nicotine eventually produces feelings of pleasure and well-being. The listed statements are descriptions of the events that happen in the cellular response to nicotine. Place the events in the correct order to describe the steps in the signaling pathway.

A) The acetylcholine receptor is an ion channel, and when a ligand binds, the ion channel opens.

B) An influx of ions carries the signal to the reward areas of the brain.

C) Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine.

D) The signal causes release of dopamine in the brain, which causes good feelings.

E) Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings).

The correct order of events is:

C) Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine.

A) The acetylcholine receptor is an ion channel, and when a ligand binds, the ion channel opens.

B) An influx of ions carries the signal to the reward areas of the brain.

D) The signal causes release of dopamine in the brain, which causes good feelings.

E) Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings).

Explanation:

Nicotine acts on acetyl cholinergic receptors that are located in membranes of the midbrain neurons. Nicotine can activate those receptors or block them more efficiently than acetylcholine. Stimulation of nicotinic receptors leads to an increase in ions flow that reaches the brain and causes dopamine release in the nucleus accumbens through axonal prolongations of the dopaminergic pathway. This response is responsible for the smoker's recompense sensation.

The dopaminergic pathway is the most important way in the process of nicotine dependence and addiction to the drug.