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. Seminal vesicle: Located posterior to the bladder; contributes fluid to semen but does not surround the urethra.
B. Urethra: The tube that passes through the prostate; not a gland itself.
C. Bulbourethral gland: Located below the prostate; much smaller in size.
D. Prostate: The prostate gland is about the size of a golf ball, located just below the bladder, and encircles the prostatic urethra.
E. Ejaculatory duct: Passes through the prostate but is not the structure described.
Correct Answer is {"dropdown-group-1":"B","dropdown-group-2":"C"}
Explanation
A. Visceral layer of the serous pericardium; myocardium:
The visceral pericardium lies on top of the myocardium, but no pericardial fluid is between them.
B. Visceral layer of the serous pericardium; epicardium:
The visceral layer is the epicardium, so this is redundant.
C. Parietal layer of the serous pericardium; visceral layer of the serous pericardium:
The pericardial cavity lies between these two layers and contains pericardial fluid to reduce friction during heartbeats.
D. Myocardium; endocardium:
This is internal to the heart and not where pericardial fluid is located.
E. Epicardium; myocardium:
Again, this space contains muscle and connective tissue, not fluid.
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