The PCA muscle is located on the back of the larynx, behind and lateral to the arytenoid cartilage. It pulls on the arytenoid cartilage to open the vocal cords for breathing. The effect of contraction of this muscle can be visualized as the opposing effect of contraction of the LCA muscle. The PCA muscle is strongly activated by sniffing. During a brisk inhale through the nose, the PCA muscle contracts and each vocal process moves laterally, increasing the size of the opening of the glottis.
Additionally, contraction of the PCA muscle can be viewed when a person initiates sound with excess tension. The LCA muscle brings the vocal cords together but then the PCA muscle also contracts and pulls the vocal processes slightly apart. The actual belly of the muscle can be seen bulging behind or posterior to the arytenoids.
Direct Visiblity: Left: the relaxed right PCA muscle’s bulk between the left arrows is small. Right: the right PCA muscle has contracted, (pulling the vocal cords slightly apart) and the increased thickness of the right PCA muscle is visible between the right arrows.