A man can get an erection by imagination, he can get an erection by touch, he can actually get an erection at night when he falls asleep, and he can even get a morning erection by the next morning. Both are erections, but their principles are related to different neural activities. Erections all look the same, but the principles vary. Psychological activity, mechanical stimulation, and the lifting of brain inhibition can all lead to an erection. Psychological erection When a man is excited by auditory, visual, olfactory, and thinking and imagining stimuli about sexual content that excite the cerebral cortex and are transmitted through the erectile center of the thoracolumbar segment of the spinal cord and act on the cavernous body of the penis, it causes the arterial blood vessels to expand and a large amount of blood to flow into the cavernous body of the penis; when the venous vessels contract and less blood flows out of the cavernous body, blood is fully retained in the rich blood vessels and blood sinuses in the cavernous body, making The penis rapidly produces a psychogenic erection. Conversely, when the arterial vasculature constricts, the blood flow into the cavernous body of the penis decreases; the venous vessels dilate and the abundant blood flow trapped in the cavernous body returns rapidly, and the penis regains weakness. Reflex Erection While the external genitalia are stimulated by local stimulation such as direct touch, walking, or internal stimulation of the rectum and bladder, reflex erection can be caused by stimulating the lower erectile center in the sacral medulla of the spinal cord to stimulate its sexual excitement. Erections are innate, and male fetuses can become erect in the womb. A young boy may also become erect and hard when urinating after birth, and sometimes lying there to pee can cause urine to spray straight into the adult’s face like a spring, often bringing unexpected laughter and joy to the parent changing the diaper, but the erection does not have any “sexual” meaning at this time. Any stimulation of the genitals themselves can cause a reflex erection, which is regulated by the pubic nerves and the sacral erectile center. These two types of psychological and physiological stimuli can work individually, but can also interact and be involved in sexual activity together. For example, when a spinal cord injury occurs above the thoracolumbar region, the patient can only have an erection with physical stimulation of the genitals, and the ability to have a psychological erection is lost. When motor neuron injury occurs below the level of the thoracolumbar region, stimulation of the genitalia cannot cause an erection, while 24-57% of patients still experience a psychogenic erection, meaning that psychogenic stimulation can be delivered through the thoracolumbar pathway. When spinal cord injury occurs in lumbar 2 to sacral 1, both psychological and reflex erections are present, but the two cannot be coordinated and ejaculatory orgasm is not possible through genital stimulation. Nocturnal erection In addition to psychological erection and reflex erection, normal men have a nocturnal erection. Men’s sleep is always in the alternation of fast-acting eye sleep and slow-acting eye sleep periods, and they also experience the physiological process of erection─weakness─re-erection─weakness, which is medically known as nocturnal erection of the penis, a normal physiological process for healthy men. Generally speaking, men will have 4 to 6 erections each night, 20 to 40 minutes each time, with a total erection of up to two and a half hours. This is because the brain always inhibits the occurrence of sexual reactions during the day, otherwise men inevitably encounter embarrassing situations from time to time, but after sleep, the brain of this inhibitory function disappears, the penis will spontaneously appear erectile response, which is completely normal, do not worry. The time, frequency and hardness of erections at night will decrease with age, while puberty to about 20 years old is the strongest. Whether it’s a psychological or reflex erection, the penis quickly returns to its normal state after external stimuli are removed. Nocturnal erections are no exception. The penis definitely weakens automatically after a period of erection, because when blood is allowed to remain in the corpus cavernosum for a long time, the blood becomes deprived of oxygen and accumulates a lot of metabolic waste, which is detrimental to the tissues and can lead to necrosis in severe cases. There is a disease of abnormal erection of the penis is such that the patient shows persistent enlargement, hardness, pain and blue-gray color of the penis for more than 4 to 6 hours, which is a urological emergency and needs to be treated urgently at the hospital as soon as possible. So the penis is not erect all night, but necessarily with tension and relaxation. Early morning erection is a meaningful physiological phenomenon in clinical practice. Some doctors have studied this phenomenon and found that during illness, early morning erection will be weakened or disappeared; and after recovery, early morning erection will be restored. Therefore, the early morning erection phenomenon can be used as a reference indicator of male health status. The presence or absence of an early morning erection can also be used as a reference indicator to determine the state of a man’s sexual function. When diagnosing certain ED patients, in order to exclude interference from other conditions, the doctor will link a special instrument to the patient’s private parts, which is used to detect the number and duration of erections each night, in order to more accurately assess the patient’s sexual ability.