There are four phases of the male sexual response including excitement, plateau, orgasm, and resolution.
In the excitement phase, penile erection occurs as a result of an arousing sexual situation. Accompanying erection is thickening of the scrotal skin and elevation of the testicles. In the plateau phase, there is increasing engorgement of the corpora and the glans, increasing size and elevation of the testicles, and a preejaculatory secretion that may occur at the tip of the penis as a result of discharge from the bulbo-urethral gland.
Orgasm actually consists of three phases: emission, in which seminal fluid and sperm from the epididymis, vas deferens, seminal vesicles and prostate is deposited into the urethra; ejaculation, which is the forcible expulsion of semen from the urethral opening, resulting from contractions of the peri-urethral and pelvic floor muscles combined with relaxation of the external sphincter and urogenital diaphragm; and orgasm, which is defined as the intense emotional excitement and climax that accompanies ejaculation, with considerable subjective variation.
Finally, in the resolution phase, there is loss of erection, the testicles decrease in size and drop down to the bottom position of the scrotum, and the scrotal skin regains its laxity.