ERECTION AND SEXUAL INTERCOURSE
Both types of nerve fibres reach most organs of the body. They control the rate at which your heart beats and the strength of each beat; they control your digestive processes; they control your breathing; and they control your ability to have an erection. Stimulation of the parasympathetic nerves which reach your penis leads to an inflow of blood into your penis and it becomes erect, which is why these parasympathetic nerves are called the ‘erection nerves’. But stimulation of the sympathetic nerves supplying your penis, for example by anxiety, or a sudden frightening noise, or fear, can inhibit an erection, or reduce one.
In this second system, nerve fibres which travel outside the spinal cord in the thoracolumbar trunk connect the higher centres of the brain with the penis, missing out the spinal parasympathetic nerves. Erotic stimuli perceived by the brain excite the thoracolumbar trunk and an erection follows.
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