Ejaculation of semen from the penis is caused by
A. sympathetic nerve firing, which initiates smooth muscle contraction in the epididymis, vas deferens, ejaculatory ducts, prostate, and seminal vesicles.
B. a somatic reflex that initiates sperm production and motility, and contracts skeletal muscle surrounding the vas deferens.
C. voluntary relaxation of the internal urethral sphincter, and sympathetic stimulation of smooth muscle contraction in the walls of the ureters and the urethra.
D. a parasympathetic reflex that contracts the seminal vesicles, epididymis, and vas deferens.
E. parasympathetic stimulation of smooth muscle in the ureters, urinary bladder, and urethra.
Answer: A
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