motivation
A need or desire that energizes and directs behavior.
instinct
A complex behavior that is rigidly patterned throughout a species and is unlearned.
drive-reduction theory
The idea that a physiological need creates an aroused tension state (a drive) that motivates an organism to satisfy the need.
homeostasis
A tendency to maintain a balanced or constant internal state; the regulation of any aspect of body chemistry, such as blood glucose, around a particular level.
incentive
A positive or negative environmental stimulus that motivates behavior.
hierarchy of needs
Maslow's pyramid of human needs, beginning at the base with physiological needs that must first be satisfied before higher-level safety needs and then psychological needs become active.
glucose
The form of sugar that circulates in the blood and provides the major source of energy for body tissues. When its level is low, we feel hunger.
set point
The point at which an individual's "weight thermostat" is supposedly set. When the body falls below this weight, an increase in hunger and a lowered metabolic rate may act to restore the lost weight.
basal metabolic rate
The body's resting rate of energy expenditure.
anorexia nervosa
An eating disorder in which a person (usually an adolescent female) diets and becomes significantly (15 percent or more) underweight, yet, still feeling fat, continues to starve.
bulimia nervosa
An eating disorder characterized by episodes of overeating, usually of high-calorie foods, followed by vomiting, laxative use, fasting, or excessive exercise.
binge-eating disorder
Significant binge-eating episodes, followed by distress, disgust, or guilt, but without the compensatory purging, fasting, or excessive exercise that marks bulimia nervosa.
sexual response cycle
The four stages of sexual responding described by Masters and Johnson�excitement, plateau, orgasm, and resolution.
refractory period
A resting period after orgasm, during which a man cannot achieve another orgasm.
estrogens
Sex hormones, such as estradiol, secreted in greater amounts by females than by males and contributing to female sex characteristics. In nonhuman female mammals, estrogen levels peak during ovulation, promoting sexual receptivity.
testosterone
The most important of the male sex hormones. Both males and females have it, but the additional levels in males stimulates the growth of the male sex organs in the fetus and the development of the male sex characteristics during puberty.
sexual orientation
An enduring sexual attraction toward members of either one's own sex (homosexual orientation) or the other sex (heterosexual orientation).