A - E, F - O, P - Z

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. Food is absorbed through the stomach and intestines. When tobacco is smoked, nicotine is absorbed through the lungs.

acetylcholine: A neurotransmitter that may function 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 a disease or condition that has a relatively rapid onset, marked intensity and a short duration.

addiction: A chronic brain disorder characterized by the loss of control of drug-taking behavior, despite adverse health, social, or legal consequences to continued drug use. Addiction is characterized by relapses during recovery.

adenosine: A neurotransmitter that binds to the adenosine receptor. Adenosine is a by-product of ATP metabolism and is an important regulator of sleep. Caffeine is an adenosine antagonist.

agonist: A chemical that produces a response, such as excitation or inhibition of action potentials when it binds to a specific receptor. Opiates, cannabis, nicotine, and some hallucinogens are agonists.

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: The principle that a nerve fiber will respond maximally or not at all to a stimulus. The strength of the impulse is not dependent on stimulus strength.

amphetamine: Stimulant drugs whose effects are very similar to cocaine.

amygdala: A part of the brain that is an important component of the limbic system.

anandamide: The neurotransmitter produced in the body that binds to the cannabinoid receptor; this receptor also binds THC, the psychoactive component in marijuana.

antagonist: A chemical that, when it binds to a receptor, blocks the receptor and prevents it from responding. Antagonists prevent agonists from binding, or attaching, to the receptor. Antagonists include caffeine and naloxone.

axon: The fiber-like extension of a neuron by 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.

astrocyte: A type of glial cell that provides nutrients, support, and insulation for neurons of the central nervous system.

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 is said to "bind" 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 major route by which the forebrain sends information to, and receives information from, the spinal cord and peripheral nerves.

buprenorphine: A long-lasting opiate analgesic that has both opiate agonist and antagonist properties. Buprenorphine may be useful for treating heroin addiction.

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: 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.

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, face recognition in vision, and some aspects of music perception and production.

cerebrum: The upper part of the brain consisting of the left and right hemispheres.

chronic: Refers to a disease or condition that persists over a long period of time.

cocaine: A highly addictive stimulant drug derived from the coca plant that produces profound feelings of pleasure.

craving: Hunger for drugs. It is caused by drug-induced changes that arise from a need of the brain to maintain a state of homeostasis that includes the presence of the drug.

dendrite: The specialized branches that extend from a neuron's cell body and function to receive messages from other neurons.

depressants: Drugs that relieve anxiety and produce sleep. Depressants include barbiturates, benzodiazepines, and alcohol.

dopamine: The neurotransmitter that produces feelings of pleasure when released by the brain reward system.

dopamine transporter: A protein structure on the cell membranes of axon terminals of dopamine-releasing neurons that carries dopamine back into the presynaptic neuron thereby rapidly removing dopamine from the synapse.

drug: A chemical compound or substance that can alter the structure and function of the body. 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: The continued compulsive use of drugs in spite of adverse health or social consequences.

ecstasy (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 opiate-like effects that bind to opiate receptors. Endorphins are made by neurons and used as neurotransmitters.

enkephalins: One of the endogenous opioids that binds to opiate receptors and is used as a neurotransmitter.

enzyme: A large molecule that living organisms use to catalyze 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 acts to elicit an action potential or make 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.

A - E, F - O, P - Z