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It takes about seven seconds from the moment of inhalation for the nicotine to pass through the lungs to the bloodstream, crossing the blood brain barrier and penetrating your brain.
Once it arrives in the brain, the nicotine floats by the various receptors and binds to receptors at the cholinergic system. As we explained in Session Three, nicotine is a psychoactive drug, and it manages to 'fool' the 'gate keeper', the receptor. It then binds to the receptor instead of a naturally occurring substance, acetylcholine that was designed for the receptor.
Nicotine occupies the receptor site, and hence it becomes a blocking agent.
With the continuous and repetitive introduction of nicotine our brain develops tolerance and dependency.
Tolerance is a phenomenon that is similar in all psychoactive drugs. What it means is that the body becomes used to the effect of the foreign substance and so, in order to get the same desired effect, the drug user needs to introduce a larger quantity of it. In this case, it means increasing the amount of cigarettes smoked per day.
The blocking effect of nicotine in the cholinergic system causes an increase in acetylcholine production. As long as there's a sufficient level of nicotine in the blood, this excess of acetylcholine is disintegrated by certain enzymes as a counter-effect. However, when nicotine levels drop due to tobacco abstinence, the addicted person experiences a 'nicotine withdrawal syndrome, resulting from an excess of acetylcholine that floods the brain, causing agitation and stimulation.
Let us now look at the steps that lead to physical dependency: |
1. Nicotine interferes with the natural operation of a specific brain system known as the cholinergic system.
2. By binding to a neural receptor instead of the original natural neurotransmitter, acetylcholine, nicotine blocks the effect of the natural substance.
3. The brain increases its level of acetylcholine to overcome the nicotine blockade.
4. The brain system develops tolerance to nicotine. The smoker needs to increase his or her level of smoking in order to get the same desired effect.
5. After continuous use of nicotine, the brain learns to accept nicotine interference as normal. From this moment on, a physical dependency is established. The brain increases the production of acetylcholine on a regular basis, and it now needs the nicotine in order to function 'normally'.
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