Ejaculation occurs when system stimulates smooth muscle of the ductus deferens, ejaculatory ducts, and the prostate gland to

Ejaculation occurs when the sympathetic nervous system stimulates smooth muscles of the ductus deferens, ejaculatory ducts, and the prostate gland to contract.
The sympathetic nervous system has to do with many actions in our bodies, but also has an important effect on men during the state of sexual arousal. It affects their reproduction organ to fulfill the actions it was created to do during sexual intercourse.

Parasympathetic nervous system; contract
Ejaculation is a response to the stimulation of an erect penis. Semen is released during ejaculation, which consists of the necessary fluid and cells to carry out the process of fertilization. During ejaculation, the seminal vesicles also contract so that their fluid is added to the semen. The contraction of the internal urethral sphincter prevents urine from entering the semen and the also keeps the semen from entering the bladder.