Ejaculation

Ejaculation is the "forcible, sudden expulsion; especially expulsion of semen from the male urethra, a reflex action that occurs as a result of sexual stimulation."

Ejaculation

Sperm travels from the epididymis through the vas deferens mixing with fluids from the male accessory glands as it enters the urethra. Rhythmic contractions of the pelvic floor and bulbospongiosus muscles push the semen towards the urinary meatus expelling it from the penis in several spurts.

(The following text or part of it is quoted from the free Wikipedia article Ejaculation:)

Ejaculation is the discharge of semen (the ejaculate; normally containing sperm) from the male reproductive tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. Ejaculation can occur spontaneously during sleep, and is a normal part of human sexual development (a nocturnal emission or "wet dream"). In rare cases, ejaculation occurs because of prostatic disease. Anejaculation is the condition of being unable to ejaculate. Ejaculation is usually very pleasurable for men; dysejaculation is an ejaculation that is painful or uncomfortable. Retrograde ejaculation is the condition where semen travels backwards into the bladder rather than out of the urethra.