Neuronal Stimulus for Performance of the Male Sexual Act
The most important source of sensory nerve signals for initiating the male sexual act is the glans penis. The glans contains an especially sensitive sensory end-organ system that transmits into the central nervous system that special modality of sensation called sexualsensation. The slippery massaging action of intercourseon the glans stimulates the sensory end-organs, and the sexual signals in turn pass through the pudendal nerve, then through the sacral plexus into the sacral portion of the spinal cord, and finally up the cord to undefined areas of the brain.
Impulses may also enter the spinal cord from areas adjacent to the penis to aid in stimulating the sexual act. For instance, stimulation of the anal epithe-lium, the scrotum, and perineal structures in general can send signals into the cord that add to the sexual sensation. Sexual sensations can even originate in internal structures, such as in areas of the urethra, bladder, prostate, seminal vesicles, testes, and vas deferens. Indeed, one of the causes of “sexual drive” is filling of the sexual organs with secretions. Mild infection and inflammation of these sexual organs sometimes cause almost continual sexual desire, and some “aphrodisiac” drugs, such as cantharidin, increase sexual desire by irritating the bladder and urethral mucosa, inducing inflammation and vascular congestion.
Psychic Element of Male Sexual Stimulation. Appropriatepsychic stimuli can greatly enhance the ability of a person to perform the sexual act. Simply thinking sexual thoughts or even dreaming that the act of inter-course is being performed can initiate the male act, culminating in ejaculation. Indeed, nocturnal emissions during dreams occur in many males during some stages of sexual life, especially during the teens.
Integration of the Male Sexual Act in the Spinal Cord.
Although psychic factors usually play an important part in the male sexual act and can initiate or inhibit it, brain function is probably not necessary for its per-formance because appropriate genital stimulation can cause ejaculation in some animals and occasionally in humans after their spinal cords have been cut above the lumbar region. The male sexual act results from inherent reflex mechanisms integrated in the sacral and lumbar spinal cord, and these mechanisms can be initiated by either psychic stimulation from the brain or actual sexual stimulation from the sex organs, but usually it is a combination of both.
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