Nicotine is the addictive and active ingredient in tobacco. Tobacco usage can therefore become addictive despite the way it is transported. Cigarettes are one of the hardest drugs, legal or otherwise, to quit. The difficulty in quitting this substance lies in the addictive properties of nicotine.
Pervasiveness
The nervous and endocrine systems are the two major communication networks in the body. The nervous system takes in sensory information from the body's internal and external environments, processes it, and sends out directions that lead to a desired effect. This complexity of this network is mediated by two important components, neurotransmitters, or chemicals that talk to the cells, and receptors. Neurotransmitters bind to receptors on cells, and the receptors transfer the information inward to the cell. There are many different receptors, but the nicotinic receptor is probably the most pervasive, or highly concentrated, of them all. This is because there are more than 100 billion neurons, or nerve cells, in the body. The Canadian Institutes of Health Research notes that the nicotinic receptors were given this name because nicotine, like its respective neurotransmitter, acetylcholine, are uniquely structured to bind to this receptor, like a lock and key.
Stimulates Brain Reward Centers
Nicotine is a very small molecule. The two main parts of the nervous system are the brain and spinal cord, or central nervous system, and then the rest of the body. The Canadian Institutes of Health Research notes that the small size of nicotine molecules allows them to freely move past the blood-brain barrier, the selective netting that protects the brain, and into the brain tissue. When it gets into the brain, a November 2000 article in the "Respiratory Reviews" magazine notes that it can stimulate those acetylcholine-nicotinic receptors within the midbrain, the emotional center of the brain. In the midbrain, the nicotine that binds to the receptors triggers the release of another brain chemical, dopamine. Increased dopamine output, according to the "Respiratory Reviews" article, is the substance thought to contribute to the addictive properties of nicotine and many other addictive substances.
Transient Effect
The fleeting effect of nicotine that calls its consumers to puff cigarette after cigarette, which may be between 20 and 40 per day in heavy smokers, is caused by receptor desensitization. The "Respiratory Reviews" article notes that the nicotine acquired from smoking one cigarette is enough to start the addictive process. Even this small amount of nicotine can produce long-lasting changes in dopamine production. Additionally, nicotine appears to saturate the receptors so much in this short period of time that they easily become desensitized. This means that without an available nicotine source, the body feels deprived. The California Quits Information Clearinghouse fact sheet notes that between cigarettes, dopamine levels decrease and withdrawal symptoms begin because the body and brain are craving the pleasure attributed to the previously increased levels of dopamine.
Accomodation
Nicotine's transient effects make it a substance that the body feels it continually needs to maintain a phony type of "high." The Health Canada website notes that new smokers experience emotional changes that resemble a feeling of increased energy, awareness and function. However, as the body gets used to the presence of nicotine over time, the production of its own stimulating chemicals may take a backseat. The body feels that it does not have to work hard to produce certain neurotransmitters and over time production will lessen, if not stop. Health Canada notes that smokers continue with cigarettes to avoid the withdrawal feeling caused by the body's new accommodation. After some time, people will not smoke to feel good, but instead to just maintain a sense of normalcy.
