How to Sing Stronger: Vocal Fold Adduction

Closing the Gap: The Intrinsic Muscles

The vocal folds are open or abducted for inhalation. When we take a deep breath, the vocal folds are fully abducted. When we speak or sing, the folds should adduct or come together at the onset of phonation; they subsequently vibrate open and closed during phonation.

The glottis or space between the vocal folds is closed by the intrinsic muscles. All the intrinsic muscles other than the transverse interarytenoid are paired muscles- there are two of each. The intrinsic muscles are:

• The paired thyroarytenoid (TA) and vocalis (the medial part of the TA) muscles.
• The paired cricothyroid (CT) muscles that tilt the thyroid cartilage forward and lengthen the folds for high notes.
• The paired lateral cricoarytenoid (LCA) and interarytenoid (IA) muscles and the unpaired transverse interarytenoid muscle; these muscles help bring the vocal folds to the midline to initiate phonation by approximating the arytenoid cartilages.

The intrinsic muscles control:

• The adduction (closing or bringing to the midline) and abduction (opening or separating) of the vocal folds.
• The adjustments in length, stiffness, and thickness of the vocal folds.

Let’s compare the function of the muscles that adduct the folds (bring them together) and the muscles that abduct (move them apart) and learn how they work together.

THE MUSCLES OF ADDUCTION

These muscles close the glottis by bringing the vocal folds to the midline to initiate phonation. This creates resistance to the air that results in increased subglottal pressure.

1. Thyroarytenoid (TA) muscles (paired):

Attached to both the thyroid and arytenoid cartilages, these paired muscles contract to shorten and relax the folds, reducing the space between them. The TA muscle is a triangular band originating at the thyroid cartilage and inserted into the arytenoid cartilage running parallel with the vocal ligament to which it is attached. The deep inner slow-twitch fibers of the TA comprise the vocalis muscle.

The primary function of the thyroarytenoid/vocalis muscles is to adjust the tension in the vocal folds to vary tone quality and pitch in the lower register. They draw the arytenoid cartilages forward toward the thyroid cartilage, relaxing and shortening the ligament. We use TA dominant vocal production when we speak, and when we sing in the lower register.

2. Lateral Cricoarytenoid (LCA) muscles (paired):

Attached to the cricoid and the arytenoid cartilages, the LCA muscles adduct, elongate, and thin the vocal folds. They adduct (bring together) the vocal folds at the posterior (back) end of the larynx by rotating the arytenoid cartilages.

As longitudinal tension on the vocal folds increases when we sing higher pitches, the glottis tends to develop a gap in the middle.

To counteract this tendency, the lateral cricoarytenoids (LCA) are contracted, pulling forward on the arytenoid cartilages and closing the glottis where the gap occurs. This process is referred to as medial compression.

Medial means in the middle. Medial compression is the drawing toward the midline action that brings the arytenoid cartilages together and closes the posterior gap in the glottis, creating resistance to subglottal air pressure.

3. Interarytenoid (IA) muscle (transverse unpaired, oblique paired):

These muscles are made of two different muscle fibers; the oblique and the transverse. They are both responsible for bringing the arytenoid cartilages together to initiate phonation. The IA muscle is especially important in providing medial compression to close the glottis at the back. Medial compression causes the vocal folds to squeeze together tighter to resist the air pressure from the lungs.

Oblique IA: The oblique interarytenoids are a pair of muscles that form an X in the back of the larynx, bringing the arytenoid cartilages together and closing the posterior gap in the glottis.

Transverse IA: The transverse IA also adducts the arytenoid cartilages. It stretches across the back underneath the oblique X shaped fibers. The transverse IA is the only unpaired intrinsic muscle.

THE MUSCLES OF ABDUCTION

These muscles move the folds apart and open the glottis for breathing. The vocal folds abduct, or open, whenever we inhale air. The muscles that govern abduction are:

1. Posterior Cricoarytenoid (PCA) muscles

CLOSED QUOTIENT

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