How is an erection produced?
When a man is sexually aroused, the blood vessels in the penis relax and open, allowing blood to fill them. The trapped blood under high pressure creates an erection. Ejaculation is a reflex action controlled by the central nervous system.
Sexual arousal
The first precondition for erection is sexual arousal. This desire arises from the brain. Whether it is touch, memory, sight, smell or fantasy: sexual arousal can be triggered by very different stimuli. The most important control centers are the cerebrum, the limbic system and the hypothalamus (an area of the diencephalon).
The limbic system and the hypothalamus, on the other hand, react involuntarily and are therefore not subject to volition. The limbic system is a very old area of the brain that is sometimes referred to as the emotional center. The arousal stimulated by these areas of the brain is mainly traced back to the sexual drive and is spontaneous. It is also referred to as the arousal reflex. The hypothalamus regulates the release of messenger substances essential for desire and erection.
The erection process
The arousal reflex generated in the brain reaches the penis via nerve pathways. On the way there and in the penis itself, messenger substances are released. This initially causes dilation of the smooth vascular muscle cells in the arteries leading to the penis and the corpora cavernosa of the penis.
The tunica albuginea (the membrane surrounding the corpora cavernosa) helps trap blood in the corpora cavernosa, maintaining erection.
This causes increased blood flow to the corpora cavernosa. The penis fills with blood and dilates. Due to the pressure of the corpora cavernosa, the veins of the penis constrict. Therefore, the blood cannot drain and the erection is maintained. In a full erection, the volume of blood in the penis is 7 to 10 times the size of a flaccid penis.
All physical processes are regulated by messenger substances. In case of erection, the arousal reflex initiates a chain reaction via the hypothalamus. In simplified form, it looks as follows: first, nitrogen oxide (NO) is released and distributed with the blood circulation. This in turn ensures that, during sexual arousal, the brain releases a messenger substance called cyclic guanine monophosphate (cGMP) into certain cells of the blood vessels. This messenger substance activates protein kinase B. It is decisively responsible for the relaxation of the smooth muscles of the blood vessels. Therefore, more blood can flow through the arteries of the penis and the corpora cavernosa. The penis hardens.
How does ejaculation occur?
Sexual stimulation and friction provide the impulses that are sent to the spinal cord and brain. Ejaculation is a reflex action controlled by the central nervous system. It is triggered when the sexual act reaches a critical level of arousal. It has two phases.
-In the first phase, the vas deferens (the tubes that store and transport sperm from the testicles) contract to push the sperm toward the base of the penis, and the prostate gland and seminal vesicles release secretions to produce semen. At this stage, ejaculation is unstoppable.
-In the second phase, the muscles at the base of the penis contract every 0.8 seconds and expel semen from the penis in up to five jets.
