**Question:** Secretomotor fiber to parotid salivary gland is supplied by?

**Core Concept:** The secretomotor fibers are a part of the parasympathetic nervous system that control the secretomotor function of salivary glands. In this case, we are discussing the supply to the parotid salivary gland.

**Why the Correct Answer is Right:** The correct answer, **C. vagus nerve (CN X)**, represents the main parasympathetic trunk that carries secretomotor fibers to the salivary glands, including the parotid gland.

**Why Each Wrong Option is Incorrect:**

A. **Sympathetic trunk (CN V):** The sympathetic trunk, specifically the glossopharyngeal nerve (CN IX), carries the secretory and vasomotor fibers to the salivary glands, but not secretomotor fibers.

B. **Spinal nerves:** Spinal nerves are involved in sensory and motor functions and do not specifically supply secretomotor fibers to salivary glands.

D. **Pharyngeal plexus (CN IX):** The pharyngeal plexus is part of the sympathetic nervous system and does not carry secretomotor fibers to the salivary glands.

**Clinical Pearl / High-Yield Fact:** The salivary glands have a dual innervation from both the sympathetic and parasympathetic nervous systems. This dual innervation contributes to the complex regulation of saliva secretion and helps maintain the balance between saliva secretion and reabsorption.

**Correct Answer:** **C. vagus nerve (CN X).** Secretomotor fibers to the parotid gland are supplied by the vagus nerve (CN X), which is a part of the parasympathetic nervous system. The vagus nerve carries secretomotor fibers to the salivary glands to regulate their secretomotor function, such as saliva secretion.