How does ejaculation occur?
Sexual stimulation (physical and/or mental) causes nerves in the penis to send chemical messages to the spinal cord and the brain. Brain chemicals help relay messages of stimulation throughout the brain, while nerve signals from the brain carry these messages to the rest of the body through the spinal cord to the male reproductive organs. When a man reaches a certain level of excitement during this process, chemical and nerve messages sent to the pelvis cause ejaculation. While not completely understood, it is believed that the chemical serotonin plays a major role in this process.
Ejaculation is the release of semen from the penis. Ejaculation involves mainly two phases. The first process through which the components of semen are released from the male reproductive organs (prostate, seminal vesicle, vas deferens) is called emission. During this process semen is deposited into the urethra (urine channel). The second phase (ejaculation proper, evacuation) is a reflex that causes rhythmic contractions of the muscles around the urethra, which propels the semen through the urethra and from the penis.
What are the components of semen?
Semen is the fluid releases from the penis upon ejaculation. Semen is made up of two parts: 1) sperm from the vas deferens and 2) seminal fluid which contains fluid from mainly the prostate gland and seminal vesicles.
Each time a male ejaculates, normally between 50- to 500-million sperm are released. However, they make up only about 2-5% of the volume of semen. The bulk of the semen is composed of the ejaculate fluid portion of semen. Men produce between 1 ml and 5 mls of semen during each ejaculation.