The Brain: Understanding Neurobiology
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National Institutes of Health
National Institute on Drug Abuse website

The Brain: Understanding Neurobiology

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A – L, M – Z

magnetic resonance imaging (MRI): An imaging technique that uses magnetic fields to generate images of the structure of the brain.

marijuana: A drug, usually smoked but it can be eaten, that is made from the leaves of the cannabis plant. The main psychoactive ingredient is THC.

medication: A drug that is used to treat an illness or disease according to established medical guidelines.

metabolism: The processes by which the body breaks things down or alters them so they can be eliminated.

methadone: A synthetic opioid used to treat pain and heroin addiction.

methamphetamine: A commonly abused, potent stimulant drug that is highly addictive and part of a larger family of amphetamines.

morphine: The most potent natural opiate compound produced by the opium poppy. Morphine is a very effective medicine for treating pain.

myelin: Fatty material that surrounds and insulates axons of some neurons.

naloxone: A short-acting opioid antagonist that binds to opioid receptors and blocks them, preventing opioids from binding to these receptors.

naltrexone: Structurally similar to naloxone, an opioid antagonist used to treat heroin addiction and, more recently, alcohol addiction.

neuron (nerve cell): A unique type of cell found in the brain and body that is specialized to process and transmit information.

neurotransmission: The process that occurs when a neuron releases neurotransmitters to communicate with another neuron across the synapse.

neurotransmitter: A chemical produced by neurons to carry messages to other neurons.

nicotine: The addictive drug in tobacco. Nicotine activates a specific type of acetylcholine receptor.

NMDA (N-methyl-d-aspartate): A synthetic amino acid that is the defining agonist for the NMDA receptor, one of the glutamate receptors on neurons.

norepinephrine: A neurotransmitter and a hormone. It is released by the sympathetic nervous system onto the heart, blood vessels, and other organs and by the adrenal gland into the bloodstream as part of the fight-or-flight response. Norepinephrine in the brain is used as a neurotransmitter in normal brain processes.

nucleus: A cluster or group of nerve cells that is dedicated to performing its own special function( s). Nuclei are found in all parts of the brain but are called cortical fields in the cerebral cortex.

nucleus accumbens: A part of the brain reward system that processes information related to motivation and reward. Virtually all drugs of abuse act on the nucleus accumbens to reinforce drug taking.

occipital lobe: The lobe of the cerebral cortex at the back of the head that includes the visual cortex.

opiate: Any of the psychoactive drugs that originate from the opium poppy or that have a chemical structure like the drugs derived from opium. Some opiates (such as opium, codeine, and morphine) are derived from the plant, while others were first synthesized by chemists.

opioid: Any chemical that has opiate-like effects; commonly used to refer to endogenous neurochemicals that activate opioid receptors but also includes natural, synthetic, and semisynthetic drugs.

opioid receptors: Receptors that recognize natural, synthetic, and endogenous opioids. When activated, they slow down or inhibit the activity of neurons on which they reside.

parallel processing: The division of an information- processing job into smaller parts that are each handled simultaneously by various cortical fields and brain nuclei.

parietal lobe: One of the four subdivisions of the cerebral cortex; it is involved in sensory processes, attention, and language.

phencyclidine (PCP): Originally developed as an anesthetic, PCP may act as a hallucinogen, stimulant, or sedative.

pituitary gland: An endocrine organ closely linked with the hypothalamus. The pituitary secretes a number of hormones that regulate the activity of other endocrine organs in the human body.

plasticity: The capacity of the brain to change its structure and function within certain limits. Plasticity underlies brain functions such as learning and allows the brain to generate normal, healthy responses to long-lasting environmental changes.

positron: A positively charged particle having the same mass and spin as, but opposite charge of, an electron.

positron emission tomography (PET): An imaging technique for measuring brain function in living subjects by detecting the location and concentration of small amounts of radioactive chemicals.

postsynaptic neuron: The neuron that receives a given message from other neurons.

presynaptic neuron: The neuron that releases neurotransmitters into the synaptic space to send messages to another neuron.

psychedelic drug: A drug that distorts perception, thought, and feeling. This term is typically used to refer to drugs with actions like those of LSD.

psychoactive drug: A drug that changes the way the brain works.

psychosocial therapy: Therapy that uses a combination of individual psychotherapy and group (social) therapy approaches to rehabilitate or provide the interpersonal and intrapersonal skills to help someone recover from drug addiction.

receptor: A protein that recognizes specific chemicals (normally neurotransmitters, hormones, and similar endogenous substances) and transmits the message carried by the chemical into the cell on which the receptor resides.

relapse: In drug abuse, relapse is the resumption of drug use after stopping. Relapse is a common occurrence in many chronic disorders, including addiction.

resting membrane potential: The difference in electrical charge between the inside and the outside of a nerve cell when the cell is not firing. The inside of a resting neuron has a greater negative charge than the outside of the neuron.

reuptake: The process by which neurotransmitters are removed from the synapse by being “pumped” through transporters back into the axon terminals that first released them.

reuptake pump (transporter): The protein that actually transports neurotransmitter molecules back into the axon terminals that released them.

reward: The process that reinforces behavior, making it more likely to recur. It is mediated at least in part by the release of dopamine into the nucleus accumbens.

reward pathway (or brain reward system): A brain circuit that, when activated, reinforces behaviors. The circuit includes the dopamine-containing neurons of the ventral tegmental area, the nucleus accumbens, and part of the prefrontal cortex. The activation of this circuit causes feelings of pleasure.

route of administration: The way a drug is introduced into the body. Drugs can enter the body by eating, drinking, inhaling, injecting, snorting, smoking, or absorption through mucous membranes.

rush: Intense feelings of euphoria a drug produces when it is first injected or smoked.

second messenger: A molecule produced inside neurons as a step in the process of communication between cells. The second messenger lets other parts of the cell know that a specific receptor has been activated, thereby completing the message carried by the neurotransmitter that bound to the receptor. Some receptors (dopamine and opiate receptors, for example) use second messengers. Others (nicotine and GABA receptors, for example) do not.

sensitization: An increased response to a drug caused by repeated administration. It is most commonly seen in some responses to stimulants.

serotonin: A neurotransmitter that regulates many functions, including mood, appetite, and sensory perception.

single photon emission computed tomography (SPECT): An imaging process that measures the emission of single photons of a given energy from radioactive tracers in the human body.

stimulants: A class of drugs that elevates mood, increases feelings of well-being, and increases energy and alertness. Stimulants include nicotine, cocaine, methamphetamine, and methylphenidate (Ritalin).

synapse: The site where presynaptic and postsynaptic neurons communicate with each other.

synaptic space (or synaptic cleft): The intercellular space between the presynaptic and postsynaptic neurons.

temporal lobe: One of the four major subdivisions of each hemisphere of the cerebral cortex. It functions in auditory perception, speech, and visual perceptions.

tetrahydrocannabinol (THC): The active ingredient in marijuana that is primarily responsible for producing the drug’s psychoactive effects.

thalamus: Located deep within the brain, the thalamus is the key relay station for sensory information flowing into the brain from the periphery. It also serves as a relay station for motor information leaving the brain to regulate function of the muscles.

tolerance: A physiological change resulting from repeated drug use that requires the user to take larger amounts of the drug to get the same effect initially felt from a smaller dose.

transporter: A large protein on the cell membrane of the axon terminals. It removes neurotransmitter molecules from the synapse by carrying them back into the axon terminal that released them.

ventral tegmental area (VTA): The group of dopamine-containing cell bodies that make up a key part of the brain reward system. These neurons extend axons to the nucleus accumbens and the prefrontal cortex.

vesicle: A membranous sac within an axon terminal that stores and releases neurotransmitter.

withdrawal: Symptoms that occur when a person who is dependent on a drug abruptly stops using the drug.

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