Definitions for the following terms were adapted from a variety of sources. Specific sources are listed in the References section.
absorption: The process by which elements move from outside of the body into the blood and other tissues. Breakdown products of food are absorbed through the stomach and intestines. When tobacco is smoked, nicotine is absorbed through the lungs.
acetylcholine: A neurotransmitter that functions in the brain to regulate memory and that controls the actions of skeletal and smooth muscle in the peripheral nervous system.
action potential: The electrical part of a neuron’s two-part, electrical-chemical message. An action potential consists of a brief pulse of electrical current that travels along the axon. When the action potential reaches the axon terminal, it triggers neurotransmitter release.
acute: Refers to an effect, disease, or condition that has a relatively rapid onset, marked intensity, and short duration.
addiction: A chronic, relapsing brain disease characterized by compulsive drug-taking despite adverse health, social, or legal consequences.
adenosine: A neurotransmitter that binds to the adenosine receptor. Adenosine is a by-product of adenosine triphosphate (ATP) metabolism and is an important regulator of sleep. Caffeine is an adenosine antagonist.
agonist: A drug that binds to a receptor of a cell and triggers a response by the cell. An agonist often mimics the action of a naturally occurring substance. Opioids, THC, and nicotine are examples.
alcohol: A psychoactively complex drug in beverages such as beer, wine, and whiskey. Alcohol is a depressant drug with potential for abuse and addiction.
all-or-none phenomenon: Used to describe an action potential and the principle that a nerve fiber will respond maximally or not at all to a stimulus.
amphetamine: Stimulant drugs with effects very similar to cocaine’s.
amygdala: A component of the limbic system involved in the expression and perception of emotion.
anandamide: A neurotransmitter produced in the body that binds to the cannabinoid receptor.
antagonist: A chemical that, when it binds to a receptor, blocks the cell from responding. Antagonists prevent agonists from binding, or attaching, to the receptor. Antagonists include caffeine (for adenosine) and naloxone (for opioids).
astrocyte: A type of glial cell that provides nutrients, support, and insulation for neurons of the central nervous system.
axon: The fiber-like extension of a neuron through which the cell carries information to target cells.
axon terminal: The structure at the end of an axon that produces and releases chemicals (neurotransmitters) to transmit the neuron’s message across the synapse.
barbiturates: Depressant drugs that produce relaxation and sleep. Sleeping pills such as pentobarbital and secobarbital are barbiturates.
bind: The attaching of a neurotransmitter or other chemical to a receptor. The neurotransmitter “binds” to the receptor.
blood-brain barrier: A network of tightly packed cells in the walls of capillaries in the brain that prevents many molecules, including poisons, from entering the brain.
brainstem: The structure at the base of the brain through which the forebrain sends information to, and receives information from, the spinal cord and peripheral nerves.
buprenorphine: A long-lasting opioid medication that has both agonist and antagonist properties. Buprenorphine is useful for treating heroin and other opioid addictions.
caffeine: A mild stimulant found in coffee and kola nuts. Caffeine is the most widely used drug in the world.
cannabinoid receptor: The receptor in the brain that recognizes anandamide and THC, the active ingredient in marijuana.
cannabis: The botanical name for the plant from which marijuana comes.
cannula: A tube that is inserted into a cavity or duct.
cell body (or soma): The central structure of a neuron, which contains the cell nucleus. The cell body contains the molecular machinery that regulates the activity of the neuron.
central nervous system (CNS): The brain and spinal cord.
cerebellum: A portion of the brain that helps regulate posture, balance, and coordination.
cerebral cortex: The outer layer of the cerebral hemispheres that controls conscious experience, including perception, emotion, thought, and planning. It also controls movement.
cerebral hemispheres: The two specialized halves of the brain. The left hemisphere is specialized for speech, writing, language, and calculation; the right hemisphere is specialized for spatial abilities, facial recognition, and some aspects of music perception and production.
cerebrum: The upper part of the brain consisting of the left and right hemispheres.
chronic: Being long-lasting and of constant or regular frequency. Can refer to a disease or condition that persists or to repeated drug use.
cocaine: A highly addictive stimulant drug derived from the coca plant that produces profound feelings of pleasure.
craving: Compulsive and uncontrollable hunger for drugs or other rewards such as food. Drug craving is caused by drug-induced changes in the brain.
dendrite: The specialized branches that extend from a neuron’s cell body and function to receive messages from other neurons.
depressants: Drugs that depress the CNS. Include sleep and anxiety medications and alcohol.
dopamine: A neurotransmitter that relays messages within the reward circuitry of the brain.
dopamine transporter: Located on the cell membrane of the axon terminal of a dopamine-releasing neuron. Terminates the neuron signal by removing dopamine from the synapse for recycling or breakdown.
drug: A chemical compound or substance that can alter the structure and function of a cellular component. Psychoactive drugs affect the function of the brain, and some of these may be illegal to use and possess.
drug abuse: The use of illegal drugs or the inappropriate use of legal drugs. The repeated use of drugs to produce pleasure, to alleviate stress, or to alter or avoid reality (or all three).
drug addiction: A chronic, relapsing brain disease characterized by compulsive drug-taking despite adverse health, social, or legal consequences.
ecstasy (methylenedioxymethamphetamine, or MDMA): A chemically modified amphetamine that has hallucinogenic as well as stimulant properties.
electroencephalogram (EEG): A graphic record of the electrical activity of the brain made by attaching electrodes to the scalp.
endogenous: Something produced by the brain or body.
endorphins: Peptides with opioid-like effects that bind to opioid receptors. Endorphins are made by neurons and used as neurotransmitters.
enkephalins: One of the endogenous opioids that binds to opioid receptors and functions as a neurotransmitter.
enzyme: A molecule that living organisms use to catalyze (speed up) chemical reactions. Enzymes are used to build, modify, or break down different molecules without themselves being permanently altered or destroyed.
excitatory neurotransmitter: A neurotransmitter that elicits an action potential or makes it more likely that one will be elicited.
exocytosis: A process by which secretory products are released from a cell via transport within vesicles to the cell surface and subsequent fusion with the plasma membrane, resulting in the extrusion of the vesicle contents from the cell.
forebrain: The largest division of the brain, which includes the cerebral cortex and basal ganglia. It is credited with the highest intellectual functions.
frontal lobe: One of the four divisions of each cerebral hemisphere. The frontal lobe is important for controlling movement, thinking, and judgment. It associates the functions of other cortical areas.
GABA (gamma-amino-butyric acid): The major inhibitory neurotransmitter in the brain.
glial cells (glia): Brain cells that support neurons by performing a variety of “housekeeping” functions in the brain.
glutamate: The most common excitatory neurotransmitter in the brain.
hallucinogens: A diverse group of drugs that alter perceptions, thoughts, and feelings. Hallucinogenic drugs include LSD, mescaline, MDMA (ecstasy), PCP, and psilocybin (magic mushrooms).
heroin: The potent, widely abused opioid that produces addiction. It consists of morphine with two acetyl groups attached to it.
hippocampus: A brain structure that is involved in learning and memory.
homeostasis: The process of keeping the internal environment of the body stable by making adjustments to changes in the external environment.
hypothalamus: The part of the brain that controls many bodily functions, including feeding, drinking, and the release of many hormones.
ingestion: The act of taking in food or other material into the body through the mouth.
inhalant: Any drug that is typically administered only by breathing in its vapors and by no other route. Inhalants commonly are organic solvents, such as glue and paint thinner, or anesthetic gases, such as ether and nitrous oxide.
inhalation: The act of administering a drug or combination of drugs by nasal or oral respiration. Also, the act of drawing air or other substances into the lungs. Nicotine in tobacco smoke enters the body by inhalation.
inhibitory neurotransmitter: A neurotransmitter that acts to prevent a neuron from firing an action potential.
injection: A method of administering a substance such as a drug into the skin, subcutaneous tissue, muscle, blood vessels, or body cavities, usually by means of a needle.
limbic system: A set of brain structures that regulates our feelings, emotions, and motivations. It is also important in learning and memory.
LSD (lysergic acid diethylamide): A hallucinogenic drug that binds to and activates the serotonin receptor.