**Question:** Facial N. stimulation during testing of nerve indicated by contraction of muscle:

A. Zygomaticus Major
B. Orbicularis Oculi
C. Masticator
D. Platysma

**Core Concept:**
The facial nerve (CN VII) is a mixed nerve consisting of sensory, motor, and autonomic components. It provides motor innervation to various muscles and sensory innervation to the face. When testing the facial nerve, the appropriate muscle contraction indicates the presence of nerve stimulation.

**Why the Correct Answer is Right:**
Correct answer D, Platysma, is the muscle that contracts when the facial nerve is stimulated. The platysma is a superficial muscle of the neck that runs from the lower angle of the mandible to the base of the skull. When the facial nerve is stimulated during testing, it triggers the contraction of the platysma muscle, indicating a normal response.

**Why Each Wrong Option is Incorrect:**
A) Zygomaticus Major (muscle of smile): This muscle is involved in facial expression, but its contraction is not indicative of facial nerve stimulation during testing.
B) Orbicularis Oculi (muscle of eyelid closure): This muscle is involved in eye closure, not related to facial nerve stimulation during testing.
C) Masticator (muscle of mastication): This muscle is involved in chewing, not related to facial nerve stimulation during testing.

**Clinical Pearl:**
In clinical practice, when facial nerve stimulation occurs during a nerve examination, it helps to confirm the integrity of the facial nerve and rule out peripheral nerve lesions. This is important in diagnosing neurological disorders affecting the facial nerve, such as Bell's palsy, stroke, or acoustic neuroma.

**Correct Answer:** Platysma (D)