How Tobacco Functions in the Brain
When a smoker inhales tobacco smoke, nicotine reaches the brain in a few seconds. Nicotine from smoking reaches the brain even faster than it would if it were injected with a needle! Spit tobacco takes a bit longer to be absorbed into the bloodstream through the gums. No matter how it enters the body, when the nicotine gets to the brain, it affects the way the billions of brain cells, or neurons, communicate with each other.
Between and around neurons are critical spaces called synapses. Neurons communicate by sending messages along their bodies and across the synapses by releasing "messenger" chemicals called neurotransmitters. When a "receiving" cell has a certain level of the neurotransmitter, it turns around and sends the message to the next neuron. Nicotine acts like a stimulant. It excites more neurons to release excess neurotransmitters. After a person takes in nicotine a few times, the brain adjusts to the new levels of these neurotransmitters. Without nicotine, the brain suddenly has a lower level of the neurotransmitters it has become used to. The addict feels uncomfortable withdrawal symptoms. The brains of addicts develop a set "necessary" level of nicotine. The addict will adjust his smoking or chewing to maintain the brain’s desired level of nicotine.