Nicotine and Neurotransmitters
Nicotine works by mimicking the structure of certain chemicals called neurotransmitters. Neurotransmitters are chemicals that neurons secrete to communicate with other cells--including other neurons, muscles and cells that secrete hormones. Neurotransmitters work by binding to special proteins called receptors, which bind to neurotransmitters based on their structure and shape. When a neurotransmitter binds to its receptor, it leads to chemicals being generated within the receptor's cell. As a presentation from the Biochemistry Department from Smith College explains, nicotine is able to bind to some of the same receptors as the neurotransmitter acetylcholine.
Absorption and Distribution
As a monograph found at the National Cancer Institute explains, nicotine begins to have its effects when absorbed in the blood. When nicotine is smoked, it's absorbed by the alveoli (located in the lungs) and is then rapidly transported throughout the body by the arterial blood. Nicotine can also be absorbed by the mucous membranes in the mouth and nose, or it can be absorbed across the skin. Once nicotine has been absorbed by the blood, it can travel throughout the body and is able to penetrate into the brain by passing through the blood-brain barrier.
Effects on Body
Actetylcholine receptors that bind to nicotine (also known as nicotinic receptors) can be found throughout the brain and the body. As a result, nicotine can cause a vast array of effects on the human body. It stimulates the adrenal glands to produce epinephrine and constricts blood vessels to muscles. It also increases stimulation throughout much of the brain. Over time, the brain responds to this increased chemical activity by decreasing the numbers of nicotinic receptors. As a result, when nicotine is not present, the brain--perceiving a lack of nicotine--responds with physical withdrawal symptoms and nicotine cravings.
