Muscle supplied by glossopharyngeal nerve:
**Core Concept**
The glossopharyngeal nerve (cranial nerve IX) is a mixed nerve that supplies various structures in the head and neck, including muscles involved in swallowing and sensory functions. The motor fibers of the glossopharyngeal nerve are responsible for innervating muscles that play a crucial role in the process of swallowing.
**Why the Correct Answer is Right**
The glossopharyngeal nerve supplies the stylopharyngeus muscle, which is a strap muscle located in the pharynx. This muscle helps to elevate the pharynx during swallowing, thereby facilitating the passage of food into the esophagus. The stylopharyngeus muscle is innervated by the glossopharyngeal nerve through its pharyngeal branch. The motor fibers of the glossopharyngeal nerve stimulate the contraction of this muscle, which is essential for the proper functioning of the pharyngeal phase of swallowing.
**Why Each Wrong Option is Incorrect**
**Option A:** (Incorrect) The hypoglossal nerve (cranial nerve XII) supplies muscles of the tongue, including the extrinsic and intrinsic muscles. These muscles are involved in movements of the tongue such as protrusion, retraction, and elevation.
**Option B:** (Incorrect) The vagus nerve (cranial nerve X) supplies various muscles in the pharynx, including the palatopharyngeus and salpingopharyngeus muscles, but not the stylopharyngeus muscle.
**Option C:** (Incorrect) The facial nerve (cranial nerve VII) supplies muscles of facial expression, including the muscles of the platysma and the muscles of the eyelid, but not the muscles involved in swallowing.
**Clinical Pearl / High-Yield Fact**
The glossopharyngeal nerve is also responsible for transmitting sensory information from the pharynx and the middle ear, including pain, temperature, and touch. This knowledge is essential for understanding the clinical presentation of glossopharyngeal nerve dysfunction, which can manifest as difficulty swallowing, ear pain, and altered taste.
**Correct Answer: D. Stylopharyngeus.**