The intrinsic muscles of the larynx that abduct the vocal cords are innervated by which nerve?

Explanation

## Innervation of Laryngeal Muscles **Key Point:** The **recurrent laryngeal nerve** (a branch of the vagus nerve) innervates all intrinsic muscles of the larynx **except** the cricothyroid muscle, which is innervated by the superior laryngeal nerve (external branch). ### Intrinsic Laryngeal Muscles and Their Actions | Muscle | Action | Innervation | Clinical Significance | |--------|--------|-------------|----------------------| | Posterior cricoarytenoid | **Abduction** of vocal cords | Recurrent laryngeal nerve | Only abductor; RLN palsy → cord in paramedian position | | Lateral cricoarytenoid | Adduction of vocal cords | Recurrent laryngeal nerve | Assists in cord closure | | Interarytenoid (transverse & oblique) | Adduction of vocal cords | Recurrent laryngeal nerve | Brings cords together | | Thyroarytenoid | Adduction & tension modulation | Recurrent laryngeal nerve | Shortens cords; lowers pitch | | Cricothyroid | Elongation & tension of cords | Superior laryngeal nerve (external) | Raises pitch; only muscle NOT innervated by RLN | **High-Yield:** The **posterior cricoarytenoid is the ONLY abductor of the vocal cords**. It is innervated by the recurrent laryngeal nerve. Bilateral recurrent laryngeal nerve paralysis leads to stridor and airway obstruction because abduction is lost. **Mnemonic:** "**LATTE**" for intrinsic muscles: - **L**ateral cricoarytenoid → Adduction - **A**rytenoid (interarytenoid) → Adduction - **T**hyroarytenoid → Adduction (and tension modulation) - **T**hyrohyoid → Not intrinsic (extrinsic) - **E**xternal cricothyroid → Tension (innervated by superior laryngeal nerve) **Clinical Pearl:** Recurrent laryngeal nerve palsy (from thyroid surgery, lung cancer, or aortic aneurysm) causes the vocal cord to rest in the **paramedian position** because: - Abductors (posterior cricoarytenoid) are paralyzed → cannot open cord - Adductors are weakened but cricothyroid (innervated by superior laryngeal nerve) can still function → cord pulled slightly medially This results in hoarseness and weak voice, but airway is usually patent (unilateral). Bilateral RLN palsy → stridor and airway obstruction.