Pathology affecting which structure would be expected to produce a sacral parasympathetic viscerosomatic reflex?

Pathology affecting which structure would be expected to produce a sacral parasympathetic viscerosomatic reflex?

• A. Ascending colon
• B. Descending colon
• C. Sigmoid colon
• D. Rectum

Answer: (B)

The sacral parasympathetic viscerosomatic reflex is driven by pelvic splanchnic nerves arising from S2–S4, which supply the hindgut. Structures in this region, such as the descending colon, sigmoid colon, and rectum, carry parasympathetic input from these sacral fibers, so pathology there can produce reflex changes in the sacral region of the spine. In contrast, the ascending colon receives parasympathetic input from the vagus nerve, not the sacral nerves, so it wouldn’t evoke a sacral parasympathetic reflex. Among the options, the descending colon is the representative hindgut structure innervated by the sacral parasympathetics, making it the best choice. (Note: sigmoid colon and rectum also have sacral innervation, but the question points to the descending colon as the classic example.)

The sacral parasympathetic viscerosomatic reflex is driven by pelvic splanchnic nerves arising from S2–S4, which supply the hindgut. Structures in this region, such as the descending colon, sigmoid colon, and rectum, carry parasympathetic input from these sacral fibers, so pathology there can produce reflex changes in the sacral region of the spine. In contrast, the ascending colon receives parasympathetic input from the vagus nerve, not the sacral nerves, so it wouldn’t evoke a sacral parasympathetic reflex. Among the options, the descending colon is the representative hindgut structure innervated by the sacral parasympathetics, making it the best choice. (Note: sigmoid colon and rectum also have sacral innervation, but the question points to the descending colon as the classic example.)