Which nerve is the motor nerve of the second pharyngeal arch?

Explanation

## Pharyngeal Arch Innervation **Key Point:** Each pharyngeal arch has a cranial nerve that provides motor innervation to the muscles derived from that arch's mesenchyme. ### Second Pharyngeal Arch (Reichert's Cartilage) **High-Yield:** The **facial nerve (CN VII)** is the motor nerve of the second pharyngeal arch. ### Muscles Innervated by CN VII from the Second Arch - Muscles of facial expression - Stapedius - Posterior belly of digastric - Stylohyoid - Platysma **Mnemonic:** **SMASH** = Stapedius, Muscles of facial expression, Anterior belly of digastric (wait—this is CN V), Stylohyoid, Hyoid muscles *Better mnemonic:* **"Second arch = Seven (CN VII)"** — the facial nerve is the seventh cranial nerve. ### Quick Reference Table: Pharyngeal Arch Nerves | Arch | Nerve | Key Muscles | | --- | --- | --- | | 1st | CN V (Trigeminal) | Muscles of mastication, tensor tympani, tensor veli palatini | | 2nd | CN VII (Facial) | Muscles of facial expression, stapedius, stylohyoid | | 3rd | CN IX (Glossopharyngeal) | Stylopharyngeus | | 4th & 5th | CN X (Vagus) | Pharyngeal and laryngeal muscles | **Clinical Pearl:** Facial nerve (CN VII) palsy results in loss of muscles of facial expression and inability to close the eye on the affected side, reflecting the second arch motor distribution.