**Core Concept**
The submandibular gland receives its preganglionic parasympathetic innervation from the facial nerve, which originates from the superior salivary nucleus in the brainstem. This nucleus is responsible for regulating the salivary glands, particularly the submandibular and sublingual glands, to produce saliva.

**Why the Correct Answer is Right**
The superior salivary nucleus sends preganglionic fibers to the geniculate ganglion, a sensory ganglion of the facial nerve. These fibers then synapse with the postganglionic neurons in the submandibular ganglion, which is located near the submandibular gland. The postganglionic fibers from the submandibular ganglion then travel through the submandibular nerve to reach the submandibular gland, causing it to secrete saliva.

**Why Each Wrong Option is Incorrect**
**Option A:** The otic ganglion is associated with the parotid gland, not the submandibular gland. It receives preganglionic fibers from the glossopharyngeal nerve, which originates from the inferior salivary nucleus.
**Option B:** The geniculate ganglion is a sensory ganglion that transmits taste information from the tongue to the brain, but it does not directly innervate the submandibular gland. The preganglionic fibers to the submandibular gland originate from the superior salivary nucleus.
**Option D:** The inferior salivary nucleus is responsible for regulating the parotid gland, not the submandibular gland. It sends preganglionic fibers to the otic ganglion, which then synapses with postganglionic neurons to innervate the parotid gland.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the preganglionic parasympathetic fibers to the submandibular gland originate from the superior salivary nucleus, which is located in the brainstem. This information can help you identify the correct pathway for salivation and distinguish it from other salivary glands.

**✓ Correct Answer: C. Superior salivary nucleus**