1 Structure
The posterior cricoarytenoid muscle is a paired intrinsic muscle of the larynx. It lies on the posterior aspect of the cricoid cartilage and forms an important part of the muscular framework that controls vocal fold position. Because it is the only muscle that opens the vocal folds, it occupies a central place in laryngeal mechanics.
1.1 Location
Each muscle is situated on the back surface of the larynx, spanning the region between the cricoid cartilage and the arytenoid cartilage. The right and left muscles sit symmetrically, one on each side of the posterior midline. Their deep position places them close to the posterior laryngeal wall and the airway lumen.
1.2 Origin and insertion
The muscle extends from the posterior cricoid lamina to the muscular process of the arytenoid cartilage. Its course is short and oblique, allowing it to act efficiently on the arytenoid cartilage during breathing and speech.
1.2.1 Origin on the posterior cricoid lamina
The origin lies on the broad posterior surface of the lamina of the cricoid cartilage. This area provides a stable bony-like cartilaginous base for muscle attachment. The origin is usually spread over a substantial part of the lamina rather than confined to a narrow point.
1.2.2 Insertion on the muscular process of the arytenoid cartilage
The fibers converge on the muscular process of the arytenoid cartilage. Contraction pulls this process posteriorly and laterally, causing the arytenoid cartilage to rotate. This rotation moves the vocal processes apart and widens the rima glottidis.
1.3 Fiber arrangement
The muscle fibers are arranged in a fan-shaped or nearly horizontal pattern. Fibers may diverge slightly as they approach the arytenoid insertion, which helps distribute force across the cartilage. The arrangement supports rapid and coordinated opening of the glottis.
1.4 Relations to neighboring laryngeal structures
The posterior cricoarytenoid muscle lies near other intrinsic laryngeal muscles, including the cricoarytenoid and thyroarytenoid muscles. It is also closely related to the laryngeal framework that supports the vocal folds. Its position behind the airway makes it especially suited to influence vocal fold abduction without directly obstructing airflow.
2 Innervation and blood supply
The muscle receives motor innervation from the recurrent laryngeal nerve and is supplied by laryngeal vessels associated with the surrounding cricoid region. These connections ensure rapid and finely timed contraction during respiration and phonation.
2.1 Nerve supply
Motor control is provided through the recurrent laryngeal nerve, the main nerve to most intrinsic laryngeal muscles. This innervation is essential for normal opening of the vocal folds.
2.1.1 Recurrent laryngeal nerve
The recurrent laryngeal nerve carries motor fibers to the posterior cricoarytenoid muscle. Because this muscle is the principal abductor of the vocal folds, damage to the nerve can seriously limit airway opening. The nerve also supplies other intrinsic laryngeal muscles, allowing coordinated control of the larynx.
2.2 Arterial supply
Blood reaches the muscle through branches associated with the laryngeal arterial network, commonly via the superior and inferior laryngeal arteries. These vessels nourish the muscle and adjacent laryngeal tissues. The arterial pattern supports the muscle’s continuous activity in breathing and speech.
2.3 Venous drainage
Venous blood drains through the corresponding laryngeal venous channels into larger neck veins. This drainage follows the general vascular arrangement of the larynx. Efficient venous return helps maintain normal tissue function in a region that is frequently active.
3 Function
The posterior cricoarytenoid muscle is best known for abducting the vocal folds. Its action regulates the size of the airway, influences airflow, and contributes indirectly to voice production by setting the position of the glottis.
3.1 Abduction of the vocal folds
When the muscle contracts, it rotates the arytenoid cartilages laterally. This movement separates the vocal folds and opens the rima glottidis. Because no other intrinsic laryngeal muscle performs this action as effectively, the muscle is considered the primary glottic abductor.
3.2 Role in respiration
During quiet breathing and especially during increased ventilatory demand, the muscle helps keep the airway open. Its activity reduces resistance to airflow through the larynx. In this way, it supports smooth inhalation and contributes to airway patency.
3.3 Contribution to phonation
Although it does not directly produce sound, the muscle influences phonation by controlling how widely the vocal folds are separated before and between vocalizations. A moderate degree of opening is necessary for normal voice onset and release. Its activity therefore helps shape the timing and quality of phonatory movements.
3.4 Coordination with other intrinsic laryngeal muscles
The muscle acts in concert with adductors and tensor muscles of the larynx. While it opens the glottis, other muscles close, tense, or relax the vocal folds for speech and airway protection. This coordination allows the larynx to switch efficiently between breathing, voice production, and protective closure.
4 Anatomy variations
The posterior cricoarytenoid muscle is usually paired and well defined, but its appearance can vary between individuals. Such variation may affect size, fiber arrangement, or the presence of additional slips.
4.1 Asymmetry between sides
The right and left muscles are not always identical in bulk or shape. Mild asymmetry is common and usually has no functional consequence. Differences may reflect normal developmental variation or individual patterns of use.
4.2 Accessory muscle slips
Some people have accessory fibers that extend from nearby structures or blend with adjacent intrinsic muscles. These slips can alter the exact route of contraction without changing the fundamental action of the muscle. Accessory bundles are generally minor anatomical findings.
4.3 Developmental considerations
Variation may arise during formation of the laryngeal musculature. Small differences in muscle migration, attachment, or differentiation can produce subtle anatomical diversity. Most such variations are recognized only during dissection or imaging.
5 Clinical significance
Because it is the main abductor of the vocal folds, the posterior cricoarytenoid muscle has major clinical importance. Disorders that impair its function can narrow the airway, affect voice, or alter laryngeal motion.
5.1 Recurrent laryngeal nerve injury
Injury to the recurrent laryngeal nerve can weaken or paralyze the muscle. Since the nerve supplies most intrinsic laryngeal muscles, damage may produce broad impairment of laryngeal movement. Loss of posterior cricoarytenoid function is particularly significant because it limits glottic opening.
5.2 Vocal fold paralysis
Paralysis affecting the muscle can leave the vocal folds unable to abduct adequately. If both sides are involved, the airway may become critically narrowed. Even unilateral dysfunction can change breathing mechanics and alter the balance of laryngeal motion.
5.3 Airway obstruction
When the muscle cannot open the glottis effectively, airflow through the larynx may be restricted. This can lead to noisy breathing, reduced exercise tolerance, or respiratory distress in more severe cases. In bilateral impairment, the obstruction may be life-threatening.
5.4 Laryngoscopic assessment
The muscle itself is not directly seen during routine examination, but its function is inferred from vocal fold movement. Laryngoscopy can show whether the folds abduct normally during inspiration. Abnormal findings may point to nerve injury or intrinsic laryngeal muscle dysfunction.
5.5 Surgical relevance
The muscle and its nerve supply are important during operations involving the neck, thyroid region, or larynx. Surgeons aim to preserve the recurrent laryngeal nerve to protect vocal fold mobility. Awareness of the muscle’s role helps explain postoperative airway and voice complications.
6 Embryology
The posterior cricoarytenoid muscle develops as part of the intrinsic musculature of the larynx. Its formation follows the general pattern of head and neck muscle development and reflects the organization of the embryonic pharyngeal apparatus.
6.1 Development of laryngeal musculature
Laryngeal muscles arise early as the primitive laryngeal structures differentiate. The posterior cricoarytenoid becomes one of the specialized muscles that govern airway control. Its development is coordinated with shaping of the laryngeal cartilages and lumen.
6.2 Formation from branchial arch mesoderm
The muscle derives from mesoderm associated with the branchial arch region. This embryonic origin explains its relationship to the nerve supply of the larynx and nearby pharyngeal structures. As development proceeds, the muscle acquires its distinctive attachment to the cricoid and arytenoid cartilages.
7 Histology
Histologically, the posterior cricoarytenoid muscle is a typical skeletal muscle adapted for rapid, precise movement. Its microscopic structure reflects the need for finely controlled laryngeal action.
7.1 Skeletal muscle characteristics
The muscle contains multinucleated striated fibers organized into bundles. These fibers are arranged to generate quick contraction and relaxation. Connective tissue layers support the fibers and transmit force to the laryngeal cartilages.
7.2 Muscle fiber types
The muscle contains a mixture of fiber types suited to both endurance and fast response. Fibers capable of rapid contraction are important for immediate glottic opening during breathing. Other fibers support sustained postural activity in the larynx.
8 Comparative anatomy
The posterior cricoarytenoid muscle is present in many mammals, though its form and emphasis vary with species-specific vocal and respiratory needs. Comparative study helps clarify how laryngeal function has adapted across vertebrates.
8.1 Differences in other mammals
In other mammals, the muscle may show differences in size, orientation, or relative prominence. Species with specialized vocal behaviors may display more elaborate laryngeal control. In many animals, however, the same basic function of vocal fold abduction is preserved.
8.2 Evolutionary significance
The muscle represents an important adaptation for controlling the airway and producing sound with precision. Its development supports the separation of breathing from vocalization. This functional specialization has been important in the evolution of complex laryngeal behavior.