How do chemicals such as nicotine work in the brain?

First, knowing how the brain works in general and how chemicals interact with neurons to alter communication between nerve cells is a good basis for understanding how the brain responds to nicotine. The brain is a complex organ comprised of gray matter and white matter. Gray matter consists of the cell bodies of neurons and other support cells. White matter consists of long tracts of axons[1] that run between the neurons (like telephone lines) in order to communicate to other brain regions. Figure 2 is an illustration of a neuron. Different areas of the brain have different functions. For example, the motor cortex controls voluntary movements, and the sensory cortex processes information from the senses (sound, sight, smell, touch, and taste). These different areas communicate with each other in an orchestrated fashion via the axons of the neurons within the areas of white matter in the brain.

The brain contains billions of neurons, which interact with each other electrochemically. This means that when a nerve is stimulated, a series of chemical events occur that in turn

A Nerve Cell (Also Called a Neuron)

Figure 2 A Nerve Cell (Also Called a Neuron)

From D. Chiras, Human Biology, 5th Edition. © 2005, Jones and Bartlett LLC.

create an electrical impulse. The resulting impulse is repeated down the nerve length (known as the axon) and causes a release of chemicals called neurotransmitters[2] into a space between the stimulated nerve and the nerve it wishes to communicate with, known as the synapse (Figure 3). The neurotransmitters interact with receptors on the second nerve, either stimulating them or inhibiting them. The interaction between the neurotransmitters and receptors can be likened to a key interacting with a lock. The neurotransmitter acts as the key and engages the receptor to unlock, causing it to open. This opening is really a structural change within the receptor on the second nerve that either causes that nerve to fire or not to fire. Brain activity is the result of an orchestrated series of nerves firing or not firing in binary fashion. It is much like a computer where very complicated processes begin as a series of ones or zeros (on or off, fire or don't fire).

Synaptic Transmission

Figure 3 Synaptic Transmission

From D. Chiras, Human Biology, 5th Edition. © 2005, Jones and Bartlett LLC.

After the nerve fires, thereby releasing neurotransmitters into the synaptic cleft, the neurotransmitters must be removed from the area in order to turn the signal off. There are two ways these chemicals can be removed in order to turn the signal off. The first is by destroying the chemical through the use of another chemical known as an enzyme[3] with that specific purpose in mind. The second is by pumping the chemical back up into the nerve that released it by utilizing another special chemical known as a transporter or transport pump[4]. The process of pumping chemicals back into the nerve is known as reuptake[5]. It is important to understand these basic principles of neurophysiology because all psychoactive compounds, whether neurotransmitters, hormones, medications, addictive drugs, or nicotine, involve one or more of these mechanisms. The differences between their effects stem from the particular receptor and neurotransmitter system with which they interact. Nicotine, like many neurotransmitters, targets a specific neurotransmitter or receptor system known as the nicotinic acetylcholine receptor. Just as nicotine targets nicotinic receptors[6], opiates target opiate receptors and marijuana targets marijuana receptors (referred to as cannabinoid receptors), which means the body produces chemicals with similar activity as their ingested cousins.

  • [1] That part of the neuron or nerve cell that is a long tube conducting neural signals away from the cell body.
  • [2] Chemicals released by nerves that communicate with other nerves causing electrochemical changes in those nerves to continue to propagate a signal.
  • [3] A biological molecule that catalyzes or accelerates a chemical reaction. Most enzymes are proteins.
  • [4] A protein involved in reuptake of neurotransmitters.
  • [5] A transporter protein located presynaptically that serves to transport a neurotransmitter back up into the neuron, essentially ending transmission between two nerves.
  • [6] Short for nicotinic acetylcholine receptors, they form ion-gated channels in certain neurons. They are located at the neuromuscular junction as well as on the postganglionic sympathetic and parasympathetic nervous system in the body. Stimulation of these receptors causes muscle contraction.
< Prev   CONTENTS   Next >