Question

ejaculation of semen from the penis is caused by

multiple choice
a parasympathetic reflex that contracts the seminal vesicles, epididymis, and vas deferens
a somatic reflex that initiates sperm production and motility, and contracts skeletal muscle surrounding the vas deferens
voluntary relaxation of the internal urethral sphincter, and sympathetic stimulation of smooth muscle contraction in the walls of the ureters and the urethra
sympathetic nerve firing, which initiates smooth muscle contraction in the epididymis, vas deferens, ejaculatory ducts, prostate, and seminal vesicles.
parasympathetic stimulation of smooth muscle in the ureters, urinary bladder, and urethra

Explanation:

During ejaculation, sympathetic nerve firing is crucial. It initiates smooth - muscle contraction in the epididymis, vas deferens, ejaculatory ducts, prostate, and seminal vesicles. This coordinated contraction helps propel semen out of the body.

• The parasympathetic system is more involved in arousal (e.g., erection) rather than ejaculation. So, options with parasympathetic (first and fifth options) are incorrect.
• Sperm production (spermatogenesis) occurs in the testes over a long period and is not initiated by a reflex during ejaculation. So, the second option is wrong.
• The internal urethral sphincter relaxation and the description in the third option do not accurately describe the main mechanism of ejaculation.

Answer:

sympathetic nerve firing, which initiates smooth muscle contraction in the epididymis, vas deferens, ejaculatory ducts, prostate, and seminal vesicles.