A. Erection
Erection is the process by which the penis elongates and becomes more rigid. Both sensory input to the glans penis and psychic stimuli lead to stimulation of sympathetic, parasympathetic nerves. The sympathetic nerves lead to inhibition of vasoconstriction while the parasympathetic nerves cause dilation of blood vessels and engorgement of the corpus cavernosum. At the same time the parasympathetic nerves stimulate contraction of the ischiocavernosus muscle to lead to decreased venous outflow from the penis. There is also relaxation of the penile retractor muscle in the bull, boar, ram and stallion.
B. Emission. This is what is meant by:
Emission is the process by which sperm move up from the cauda epididymis and into the colliculus seminalis. The sperm then mix with accessory sex gland secretions before ejaculation. The process of emission is controlled by sympathetic nerves and leads to contraction of smooth muscles of the cauda epididymis, vas deferens, seminal vesicles, prostate and closure of the sphincter of the bladder.
C. Ejaculation.
Parasympathetic nerves control the contraction of striated muscles of the ischiocavernosus, bulbospongiosus and pelvic urethra. Again stimulation of these nerves can be via tactile or psychic input. In the bull and ram, the tactile sensitivity of the penis is primarily responsive to temperature. In the boar, stallion and human, the penis is primarily responsive to pressure. The contractions of the ischiocavernosus, bulbospongiosus and pelvic urethra muscles force the semen (sperm and accessory gland secretions) to move toward the penis. Rhythmic contractions of the bulbospongiosus muscle causes temporary increases in blood pressure in the corpus spongiosum which moves as waves toward the glans penis. It is these waves of increased blood pressure and the temporary occlusion of the urethra that moves the semen out of the male.
Prostate Anatomy-Back
Prostate Anatomy-Front
