Which of the following statement regarding the sensory nerve supply of pharyngeal mucous membrane is TRUE?
## **Core Concept**
The sensory nerve supply to the pharyngeal mucous membrane is primarily provided by branches of the **trigeminal nerve (cranial nerve V)**, **glossopharyngeal nerve (cranial nerve IX)**, and **vagus nerve (cranial nerve X)**. The pharynx is divided into three main parts: the nasopharynx, oropharynx, and laryngopharynx. Each part has distinct sensory innervation.
## **Why the Correct Answer is Right**
The sensory innervation of the pharyngeal mucosa is as follows:
- The **nasopharynx** receives sensory innervation from the **pharyngeal branch of the vagus nerve (CN X)**, also known as the nerve of Arnold or Jacobson's nerve, and from the **trigeminal nerve** via the **pterygopalatine ganglion**.
- The **oropharynx** is primarily innervated by the **glossopharyngeal nerve (CN IX)**.
- The **laryngopharynx** receives sensory innervation from the **internal branch of the superior laryngeal nerve**, a branch of the **vagus nerve (CN X)**.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Without specific details on the option, we cannot directly address its inaccuracies. However, if it inaccurately describes the sensory innervation of any part of the pharynx, it would be incorrect based on the details provided above.
- **Option B:** Similarly, without specifics, if this option misrepresents the nerve supply to any section of the pharynx, it would be incorrect.
- **Option C:** This option would be incorrect if it fails to accurately reflect the complex sensory innervation provided by the trigeminal, glossopharyngeal, and vagus nerves to the pharyngeal mucosa.
## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that the **gag reflex**, which involves the sensory innervation of the oropharynx, is mediated by the **glossopharyngeal nerve (CN IX)** for the afferent (sensory) part and the **vagus nerve (CN X)** for the efferent (motor) response, leading to contraction of the pharyngeal muscles.
## **Correct Answer:** D.