Lateral Cricoarytenoid: Origin, Insertion, Nerve & The "Whisper" Muscle

The Lateral Cricoarytenoid (LCA) is a small but vital intrinsic muscle of the larynx. It is a primary adductor of the vocal folds, meaning it brings them together to close the airway for protection and phonation. It works in direct opposition to the Posterior Cricoarytenoid.

[Image of Lateral Cricoarytenoid muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Upper border of the lateral arch of the Cricoid Cartilage.
Insertion (Distal)	Anterior aspect of the Muscular Process of the Arytenoid Cartilage.
Nerve Supply	Recurrent Laryngeal Nerve (Branch of Vagus Nerve - CN X).
Blood Supply	Superior and Inferior Laryngeal Arteries.
Primary Actions	Adduction: Closes the glottis (bringing vocal cords together) by medial rotation of the arytenoids. Whispering: Closes the ligamentous part of the cords but leaves a posterior gap.

Deep Dive: The Vocal Cord Closer

To understand voice production, one must understand the interplay between the arytenoid cartilages and the intrinsic muscles.

1. The Mechanics of Adduction

When the Lateral Cricoarytenoid contracts, it pulls the Muscular Process of the arytenoid cartilage forward and laterally. Because the arytenoid pivots, this action swings the Vocal Process (where the vocal cord attaches) medially. This closes the rima glottidis (the space between the cords).

2. The "Whisper" Configuration

The LCA is often called the "whisper muscle." When it contracts without the help of the Transverse Arytenoid muscle, it brings the vocal ligaments together but leaves a small triangular gap at the back of the glottis (between the arytenoid cartilages themselves). Air escaping through this small chink creates the whispering sound.

Physio Corner: Clinical Relevance

💪 Functional Fact: The LCA acts as a sphincter for the lower respiratory tract. Before you cough or lift a heavy weight (Valsalva maneuver), the LCA clamps the vocal cords shut to build up subglottic pressure.

Assessment (Laryngoscopy)

We cannot palpate this muscle directly. It is assessed via Laryngoscopy.
Normal: Vocal cords move symmetrically toward the midline during phonation (saying "eeee").
Paralysis: The vocal cord on the affected side will stay fixed in a paramedian (slightly open) position, leading to a breathy voice and risk of aspiration.

⚠️ Clinical Pathology: Recurrent Laryngeal Nerve Injury
Because the LCA is supplied by the Recurrent Laryngeal Nerve, it is at risk during thyroid surgery. Damage to this nerve paralyzes the LCA (and all other intrinsic muscles except the Cricothyroid), resulting in hoarseness and a weak cough.

Functional Testing

Standard MMT cannot be performed on laryngeal muscles. Function is graded by voice quality and airway protection.

Clinical Signs of Weakness

• Dysphonia: Hoarseness or "breathy" voice quality because air leaks through the unclosed glottis.
• Aspiration: Choking on liquids because the vocal cords cannot close tightly to protect the trachea during swallowing.
• Weak Cough: Inability to build up the pressure required for an explosive cough.

Frequently Asked Questions

What is the antagonist to the LCA?

The Posterior Cricoarytenoid (PCA). The PCA is the only muscle that abducts (opens) the vocal cords, directly opposing the closing action of the LCA.

Does it tense the vocal cords?

Its primary job is adduction (closing). Tensing/elongating the cords (to change pitch) is primarily the job of the Cricothyroid muscle.

Why is it called "Lateral"?

It originates from the lateral aspect of the cricoid cartilage, distinguishing it from the Posterior Cricoarytenoid, which originates from the back plate of the cricoid.

Test Your Knowledge: LCA Quiz

1. What is the primary action of the Lateral Cricoarytenoid?

2. Which nerve supplies the LCA?

3. Where does the LCA insert?

4. The LCA is often referred to as the muscle of:

5. Which muscle is the direct antagonist to the LCA?

6. Where does the LCA originate?

7. Damage to the nerve supplying the LCA results in:

8. The Recurrent Laryngeal Nerve is a branch of which cranial nerve?

9. What happens to the arytenoid cartilage when LCA contracts?

10. Which muscle works with the LCA to fully close the posterior glottis?

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Netter, F. H. (2014). Atlas of Human Anatomy. 6th ed. Saunders.