Nicotine Entry
According to the National Institute for Drug Abuse, nicotine can get into the blood in a variety of ways. When it is smoked (either via cigarettes, cigars or pipe tobacco) it gets into the blood via the lungs. When chewed or sniffed, it passes across the tissues in the mouth and nose (the mucous membranes) and enters the bloodstream. Nicotine can also pass through the skin and cross into the blood vessels that supply the skin. Once nicotine has entered the blood, it is distributed throughout the body and the brain, where it can affect the nervous system.
Neurons and Neurotransmitters
The brain is made up of millions of cells called neurons. Neurons are stimulated by special chemicals called neurotransmitters, which are able to bind to special structures on the neuron called receptors. When a neurotransmitter binds to a receptor, it can activate or block the activity of the neuron. Receptors bind to neurotransmitters based on shape and electrical charge. One kind of receptor in the brain is called a nicotinic receptor. The nicotinic receptors respond to acetylcholine, which is a neurotransmitter used for signaling throughout most of the body. Nicotine, on the other hand, can also bind to and activate these receptors. As a result, nicotine in the blood is able to mimic acetylcholine and activate receptors throughout the body.
Nicotine Effects On Nerves
Nicotinic receptors are present on many tissues throughout the body, allowing nicotine to affect breathing, memory, alertness, heart rate and the movement of muscles. Prolonged nicotine exposure can cause changes to the way neurons respond to nicotine and acetylcholine. The nerves may develop fewer receptors for these chemicals and also reduce the sensitivity of the neurons to these chemicals. The end result is that more of nicotine (and acetylcholine) is needed to properly activate these nerves, leading to tolerance and dependence.
