The larynx is comprised of 10 muscles — five on each side. Each muscle can do only one thing: contract. By changing the position, length, and tension of the vocal cords, collectively they generate the full range of human voice.
Since each muscle is paired, any asymmetric contraction represents a probable weakness. Understanding the function of each muscle helps illuminate neurologic and muscular injuries with particular clarity.
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.
ThyroArytenoid Muscle (TA)
The vocal cord’s primary mass — it fills the membranous cord and is the dominant pitch-control muscle in the chest register.
CricoThyroid Muscle (CT)
Located on the outside of the larynx, it stretches the vocal cords to provide the falsetto (upper) register and easy projection.
Lateral CricoArytenoid Muscle (LCA)
Brings the vocal cords from the open breathing position to closed, rotating the vocal process to the midline for phonation.
InterArytenoid Muscle (IA)
Holds the vocal cords in the closed position after the LCA brings them together — and may receive nerve input from both sides.
Posterior CricoArytenoid Muscle (PCA)
The only abductor of the vocal cords — opens them for breathing, strongly activated by sniffing, and sometimes visible behind the arytenoids.
Compensation
The larynx’s natural tendency to hide voice disorders. Removing compensation is essential to accurate endoscopic diagnosis.