Final answer:
Masters and Johnson described the sexual response cycle in four phases: excitement, plateau, orgasm, and resolution, each with distinct physiological responses and characteristics.
Step-by-step explanation:
Masters and Johnson's studies on human sexual behavior identified four phases of the sexual response cycle: excitement, plateau, orgasm, and resolution. During the excitement phase, there's an increase in heart rate, muscle tension, and blood flow to genital areas, leading to erection in the p_enis or c_litoris and vaginal lubrication. The plateau phase involves heightened sexual pleasure with increased breathing, heart rate, and muscle tension.
Orgasm is characterized by involuntary muscle contractions, ejaculation in males, and rhythmic contractions in females. Lastly, resolution marks a return to an una_roused state with muscle relaxation and refractory periods, especially in males, during which it's not possible to achieve another orgasm for a variable period.