Which of the following explains the neural mechanism of an erection?
It is an autonomic reflex mediated predominantly by parasympathetic nerve fibers.
It is an autonomic reflex mediated predominantly by sympathetic nerve fibers.
It is a somatic reflex mediated predominantly by parasympathetic nerve fibers.
It is a somatic reflex mediated predominantly by sympathetic nerve fibers.
It is an exclusively voluntary action mediated by the cerebral cortex.
The Correct Answer is A
A. It is an autonomic reflex mediated predominantly by parasympathetic nerve fibers: Erection is primarily driven by parasympathetic stimulation (S2–S4), which causes vasodilation of penile arteries and engorgement of erectile tissue.
B. It is an autonomic reflex mediated predominantly by sympathetic nerve fibers: Sympathetic fibers are involved in ejaculation and detumescence, not erection initiation.
C. It is a somatic reflex mediated predominantly by parasympathetic nerve fibers: Erection is not mediated by somatic (voluntary) control.
D. It is a somatic reflex mediated predominantly by sympathetic nerve fibers: Both components are incorrect—erection is not somatic and not sympathetic.
E. It is an exclusively voluntary action mediated by the cerebral cortex: Erection can be influenced by psychological stimuli, but the physiological mechanism is autonomic, not voluntary.
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Related Questions
Correct Answer is D
Explanation
A. Baroreceptors: Sense blood pressure changes, not osmolarity or thirst.
B. Proprioceptors: Detect body position and movement; unrelated to fluid balance.
C. Nociceptors: Detect pain; not involved in fluid regulation.
D. Osmoreceptors: Located in the hypothalamus, they detect changes in blood osmolarity and stimulate thirst when osmolarity rises.
E. Mechanoreceptors: Respond to mechanical changes like pressure or stretch, not osmolarity.
Correct Answer is A
Explanation
A. Transverse colon: The transverse colon is the horizontal portion of the large intestine that runs across the upper abdomen from the right colic flexure (near the liver) to the left colic flexure (near the spleen).
B. Ascending colon: The ascending colon runs vertically upward along the right side of the abdomen, from the cecum to the hepatic flexure.
C. Descending colon: The descending colon runs vertically down the left side of the abdomen, from the splenic flexure to the sigmoid colon.
D. Ileum: The ileum is the final section of the small intestine, located in the lower abdomen, and connects to the cecum.
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