Muscle supplied by 9th cranial nerve:
**Core Concept**
The 9th cranial nerve, also known as the glossopharyngeal nerve, is a mixed nerve that provides sensory, motor, and parasympathetic innervation to various structures in the head and neck. Specifically, it is responsible for controlling the muscles of the pharynx and providing sensory input from the posterior one-third of the tongue.
**Why the Correct Answer is Right**
The glossopharyngeal nerve (9th cranial nerve) supplies the stylopharyngeus muscle, which is a skeletal muscle involved in the process of swallowing (deglutition). The stylopharyngeus muscle originates from the styloid process of the temporal bone and inserts into the pharyngeal constrictor muscle. It helps to elevate the pharynx during swallowing, thereby facilitating the passage of food into the esophagus. The motor fibers of the glossopharyngeal nerve synapse in the pharyngeal plexus, which is a complex network of nerve fibers that innervates the muscles of the pharynx.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the hypoglossal nerve (12th cranial nerve) is responsible for supplying the muscles of the tongue, not the pharynx.
**Option B:** This option is incorrect because the vagus nerve (10th cranial nerve) supplies various structures in the head and neck, including the parasympathetic innervation of the pharynx, but it is not responsible for supplying the stylopharyngeus muscle.
**Option C:** This option is incorrect because the accessory nerve (11th cranial nerve) supplies the sternocleidomastoid and trapezius muscles, which are involved in neck movements and not swallowing.
**Clinical Pearl / High-Yield Fact**
The glossopharyngeal nerve is also responsible for providing sensory input from the posterior one-third of the tongue, which is important for taste and sensation. Damage to this nerve can result in loss of taste and sensation in this region.
**Correct Answer:** D.