Which is not supplied by pelvic splanchnic nerves?
**Core Concept**
The pelvic splanchnic nerves are a group of nerve fibers that arise from the sacral spinal cord and provide parasympathetic innervation to various pelvic organs, including the rectum, bladder, and reproductive organs. These nerves play a crucial role in regulating the function of these organs and are part of the autonomic nervous system.
**Why the Correct Answer is Right**
The pelvic splanchnic nerves primarily carry parasympathetic fibers from the sacral spinal cord to the pelvic organs. These nerves stimulate the contraction of smooth muscle in the pelvic organs, promoting functions such as defecation, urination, and ejaculation. The pelvic splanchnic nerves also contain sensory fibers that transmit information from the pelvic organs to the central nervous system.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the pelvic splanchnic nerves do not provide innervation to the skin of the perineum. The perineal branch of the pudendal nerve is responsible for this function.
* **Option B:** This option is incorrect because the pelvic splanchnic nerves do provide innervation to the rectum. In fact, they play a crucial role in regulating rectal function, including defecation and continence.
* **Option C:** This option is incorrect because the pelvic splanchnic nerves do provide innervation to the bladder. They stimulate the contraction of the detrusor muscle, promoting urination.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the pelvic splanchnic nerves are responsible for promoting parasympathetic functions in the pelvic organs, such as defecation and urination. This is in contrast to the sympathetic nerves, which promote functions such as ejaculation and bladder storage.
**Correct Answer: A. The skin of the perineum is supplied by the perineal branch of the pudendal nerve.**