USMLE PRACTICE QUESTION #63
TOPIC: Muscular/reproductive physiology
Today’s question will test your understanding of ejaculatory physiology.
I’m Paul Ciurysek, MD, and this is The USMLE Times: An independent, subscriber-supported newsletter designed to help you survive medical school, pass your USMLE exams, and match into your dream residency program. This question and all others are free for 48 hours; after that, it’s available to Premium subscribers only.
A 25-year-old man visits his primary care physician concerned about his recent difficulty with ejaculation. He reports that he has no issues with achieving and maintaining an erection, but he is unable to ejaculate during sexual activity. His vital signs are as follows: Blood pressure 124/80 mmHg, pulse 64 beats/minute, respiratory rate 18 breaths/minute, and temperature 98.6°F (37°C). He has no significant medical history and takes no medications. Which of the following best describes the normal physiological process that enables the expulsion phase of ejaculation?
A. Contraction of the smooth muscles surrounding the vas deferens and seminal vesicles
B. Increased sympathetic stimulation of the prostate gland and seminal vesicles
C. Contraction of the bulbospongiosus and ischiocavernosus muscles
D. Relaxation of the external urethral sphincter
E. Activation of the pudendal nerve
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The mental model used to answer this question comes from our detailed test-taking skills masterclass. Here’s how to think through this question:
Step 1. Read the last line to determine what the question is asking: Identify the normal physiological process that enables the ‘expulsion’ phase of ejaculation.
Step 2: Is this a first-, second-, or third-order question?
Answer: 1st order.
Step 3: The last line provides all the necessary information, so you can use it to determine the answer.
Step 4. Ask yourself what process is responsible for the expulsion phase of ejaculation.
Step 5. Look at the answer choices and select the option most closely resembling your thoughts from “Step 4” above.
GENERAL ANALYSIS
The ejaculatory process focuses on an automatic physiological process. There are several steps to this entire process. However, one, in particular, causes the phase in question.
ANSWER CHOICES:
CHOICE A: Contraction of the smooth muscles surrounding the vas deferens and seminal vesicles
Explanation: This describes the emission phase, where smooth muscle contractions move semen into the urethra.
CHOICE B: Increased sympathetic stimulation of the prostate gland and seminal vesicles
Explanation: Sympathetic stimulation is crucial for the emission phase, facilitating the movement of semen into the urethra.
CHOICE C: Contraction of the bulbospongiosus and ischiocavernosus muscles
Explanation: Rhythmic muscle contractions are responsible for propelling semen out of the urethra during ejaculation.
CHOICE D: Relaxation of the external urethral sphincter
Explanation: Relaxation allows semen to pass through but is not solely responsible for expulsion. While this does occur during expulsion, it is not the primary action driving semen expulsion.
CHOICE E: Activation of the pudendal nerve
Explanation: The pudendal nerve plays a role in controlling pelvic floor muscles. This is involved in coordinating muscle contractions but not directly in the expulsion mechanism.
FINAL VERDICT…
The expulsion phase of ejaculation involves rhythmic contractions of striated muscles such as the bulbospongiosus and ischiocavernosus. These contractions are mediated by somatic nerves, particularly through activation by the pudendal nerve, leading to forceful ejection of semen from the urethra. This process is distinct from emission, which involves sympathetic nervous system activity to move semen into position for expulsion.
CORRECT ANSWER: C) Contraction of the bulbospongiosus and ischiocavernosus muscles
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Thanks for checking out Q63!
See you next time 👋