Erections also require neural input to redirect blood flow into the corpora cavernosae. Psychogenic erections secondary to sexual images or auditory stimuli relay sensual input to the spinal cord at T-11 to L-2. Neural impulses flow to the pelvic vascular bed, redirecting blood flow into the corpora cavernosae. Reflex erections secondary to tactile stimulus to the penis or genital area activate a reflex arc with sacral roots at S2 to S4. Nocturnal erections occur during rapid-eye-movement (REM) sleep and occur 3–4 times nightly. Depressed men rarely experience REM sleep and therefore do not have nocturnal or early-morning erections.

Men with diabetes tend to develop erectile dysfunction 10 to 15 years earlier than men without diabetes. As men with diabetes age, erectile dysfunction becomes even more common. Above the age of 50, the likelihood of having difficulty with an erection occurs in approximately 50% to 60% of men with diabetes. Above age 70, there is about a 95% likelihood of having some difficulty with erectile dysfunction.
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