The larynx is comprised of 10 muscles. With the various muscles changing the position, length and tension of the vocal cords quite a range of sounds can be generated.
There are five muscles on each side of the larynx.
- TA – ThyroArytenoid
- LCA – Lateral CricoArytenoid
- PCA – Posterior CricoArytenoid
- CT – CricoThyroid
- IA – InterArytenoid
Since each muscle is paired, any asymmetric contraction represents a probable weakness. Understanding the function of each muscle will help one understand neurologic and muscular injuries especially well.
First though, we can think about the general operation of the vocal cords. During phonation at a low pitch, the vocal cords are brought together, but tension remains relatively loose leaving the vocal cords short and thick. At high pitch, they are conversely tight, long and thin.
The muscles are hidden from our direct view, though in some cases we can see the bulk of the muscle beneath the surface. Additionally, since each muscle can do only one thing – contract – we can visualize some effect from each muscle during endoscopy if we know how to trigger contractions of that muscle.
One complicating factor is that the larynx has some redundancy in this setup and when a person develops a voice problem, she naturally compensates in the most expeditious way possible to maintain her voice. For a laryngologist, testing the individual muscles also involves unmasking this compensation.