antagonist

1. a drug or other chemical agent that inhibits the action of another substance. For example, an antagonist may combine with the substance to alter and thus inactivate it (chemical antagonism); an antagonist may reduce the effects of the substance by binding to the same receptor without stimulating it, which decreases the number of available receptors (pharmacological antagonism); or an antagonist may bind to a different receptor and produce a physiological effect opposite to that of the substance (physiological antagonism).

2. a contracting muscle whose action generates force opposing the intended direction of movement. This force may serve to slow the movement rapidly as it approaches the target or it may help to define the movement end point. Compare agonist. —antagonism n. —antagonistic adj.

Browse dictionary by letter

a b c d e f g h i j k l m n o p q r s t u v w x y z

Psychology term of the day

April 29th 2024

operant

n. a class of responses that produces a common effect on the environment. An operant is defined by its effect rather than by the particular type of behavior producing that effect. A distinction may be made between the behavior required to achieve the effect and those alternative forms of behavior that constitute the class and may also occur. In the former, the class might include all forms of behavior that result in a lever being moved 4 mm downward (see descriptive operant). In the latter case, the class includes all forms of behavior that become more probable; for example, a rat’s two-handed lever presses might increase in probability, but one-handed presses might not (see functional operant). Compare respondent.