Which nerve is the main motor nerve to the muscles of facial expression? (repeated emphasis for testing comprehension)

Which nerve is the main motor nerve to the muscles of facial expression? (repeated emphasis for testing comprehension)

• A. CN VII
• B. CN V
• C. CN IX
• D. CN X

Answer: (A)

The main motor input to the muscles of facial expression comes from the facial nerve, cranial nerve VII. This nerve carries the somatic motor fibers that innervate the mimic muscles around the face, such as the orbicularis oculi, zygomaticus, buccinator, and orbicularis oris. After it emerges from the skull and travels through the facial canal, it divides into the five major terminal branches (temporal, zygomatic, buccal, mandibular, and cervical) to reach these muscles. That’s why it’s the primary nerve for facial expressions and movements like smiling, frowning, and blinking. The other nerves listed have different primary roles. The trigeminal nerve supplies muscles of mastication (and sensation to the face), not the facial expression muscles. The glossopharyngeal and vagus nerves control throat and parasympathetic functions, and motor to different muscle groups (stylopharyngeus, pharyngeal and laryngeal muscles), rather than the facial expression muscles.

The main motor input to the muscles of facial expression comes from the facial nerve, cranial nerve VII. This nerve carries the somatic motor fibers that innervate the mimic muscles around the face, such as the orbicularis oculi, zygomaticus, buccinator, and orbicularis oris. After it emerges from the skull and travels through the facial canal, it divides into the five major terminal branches (temporal, zygomatic, buccal, mandibular, and cervical) to reach these muscles. That’s why it’s the primary nerve for facial expressions and movements like smiling, frowning, and blinking.

The other nerves listed have different primary roles. The trigeminal nerve supplies muscles of mastication (and sensation to the face), not the facial expression muscles. The glossopharyngeal and vagus nerves control throat and parasympathetic functions, and motor to different muscle groups (stylopharyngeus, pharyngeal and laryngeal muscles), rather than the facial expression muscles.