Action Potential. The brief electrical impulse that provides the basis for conduction of information along an axon. The action potential results from brief changes in membrane permeability to sodium and potassium ions.

Agonist. Literally, a contestant, or one who takes part in the contest. An agonistic drug facilitates the effects of a particular neurotransmitter on the postsynaptic cell.

Antagonist. An antagonistic drug opposes or inhibits the effects of a particular neruotransmitter on the postsynaptic cell.

Apomorphine. A drug that blocks dopamine receptors when administered at low doses. At higher doses it blocks postsynaptic receptors as well.

Catecholamine. A class of biologically active amines that includes the neurotransmitters dopamine, norepinephrines, and epinephrine.

Dopamine. A neurotransmitter; one of the catecholamines.

5-Hydroxytryptamine (5-HT). An indolamine transmitter substance; also called serotonin.

Ligand. A chemical that binds with the binding site of a receptor.

LSD. Lysergic Acid Dimethylamide.

Nucleus raphe magnus. One of the nuclei of the raphe. It contains serotonin-secreting neurons that project to the dorsal gray matter of the spinal cord via the dorsolateral columns and is involved in analgesia produced by opiates.

Post synaptic receptor. A receptor molecule in the postsynaptic membrane of a synapse that detects the presence of a neurotransmitter and controls nerotransmitter-dependent ion channels, thus producing excitatory or inhibitory postsynaptic potentials.

Raphe. A group of nuclei located in the reticular formation of the medulla, pons, midbrain situated along the midline.

Receptor blocker. A drug that attaches to postsynaptic receptors without stimulating them, thus preventing the neurotransmitter from acting on them.

Receptor cell. A specialized type of cell that transduces physical stimuli into slow, graded potentials.

REM Sleep. A period of desynchronized EEG activity during sleep, at which time dreaming, rapid eye movements, and muscular paralysis occur; also called paradoxical sleep.

Serotonin. An alternative name for the neurotransmitter 5-hydroxytryptamine (5-HT); named because of its constricting effect on blood vessels.

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