There are four parts to normal sexual function in men – sex drive (also called libido), erection, ejaculation (emission of fluid) and orgasm.

What causes sex drive?

At puberty, the brain increases production of hormones that stimulate greater production of testosterone by the testicles. Testosterone is the main hormone responsible for the development of male sex organs and sexual behaviour. When testosterone levels drop, sex drive diminishes.

This occurs naturally with ageing, but may also occur with illness, some commonly used medications and with hormone treatment for prostate cancer.

Figure 1: The male reproductive system

What happens when you have an erection?

The penis has two main chambers (the cavernosal bodies) that fill with blood when a man is sexually stimulated. This happens when nerves in the penis release a substance that causes the smooth muscle of the blood vessels (the arteries) to relax. This causes the cylinders to dilate as blood is pumped in. The penis elongates, shutting off the veins so that less blood leaves the penis than enters it. This continues until a full erection is achieved.
After ejaculation, the nerves stop releasing the muscle-relaxing substance, more blood leaves the penis than enters it and the erection subsides.

Healthy nerves and healthy blood vessels are important for erections. The nerves necessary for erections are separate from those involved in the skin sensation from the penis and those involved in orgasm.

Lifestyle factors can affect your sexual function just as they can affect your heart and general health. Not smoking, avoiding excessive alcohol intake, eating a healthy diet and exercising regularly will help improve both your fitness and your sexual function.

What happens during ejaculation?

Sperm are produced in the testes and mature in a structure close to the testes called the epididymis. Sperm are then stored in structures close to the bladder called the seminal vesicles (Figure 1). During ejaculation, semen, which contains sperm and fluid from the prostate and seminal vesicles, is propelled into the urethra (urine tube). During ejaculation, pressure builds up in the prostate region, a muscular valve at the bladder outlet closes, blocking the outflow of urine. Semen is propelled out of the penis as the pelvic floor muscles relax and contract.

What happens during orgasm?

Orgasm mainly happens in the brain and has little to do with the prostate.
As long as normal skin sensation is intact, orgasm can occur even in the absence of an erection and without ejaculation. This is a key reason why enjoyment from sexual activity can be maintained in most men after prostate cancer treatment. The common exception is men receiving hormone treatment. Hormone treatment removes the action of testosterone, frequently causing a loss of libido (sexual desire) as well as erectile function.