Your vocal cords open and close through a combination of muscle contractions, nerve signals from the brainstem, and air pressure changes in your throat. At the most basic level, small muscles attached to two tiny cartilages in your larynx rotate and slide those cartilages to pull your vocal folds apart or press them together. These movements happen hundreds of times per second during speech, yet they also occur slowly and steadily every time you breathe. Understanding what drives them means looking at three systems working together: muscles, nerves, and airflow.
The Muscles That Open Your Vocal Cords
Only one muscle in your entire body can open your vocal cords: the posterior cricoarytenoid, often called the PCA. It sits on the back of a ring-shaped cartilage at the base of your larynx and connects to two small pyramid-shaped cartilages called the arytenoids. When the PCA contracts, it rotates the arytenoids outward, pulling the vocal folds apart and widening the airway. The vocal folds swing laterally and posteriorly at roughly a 57-degree angle during this movement.
Because the PCA is the sole muscle that opens the glottis (the space between your vocal folds), damage to it or to its nerve supply can be life-threatening. If both sides fail, the vocal cords stay closed or nearly closed, blocking airflow. This is one reason bilateral vocal cord paralysis is a medical emergency.
The Muscles That Close Your Vocal Cords
While opening relies on a single muscle, closing is a team effort involving at least four muscles, each contributing something different.
- Lateral cricoarytenoid: This is the primary closer. It rotates the arytenoid cartilages inward, swinging the vocal folds toward each other and sealing the airway. It’s active during swallowing, speaking, and controlled exhaling.
- Interarytenoid: The only unpaired muscle in the larynx, it has both horizontal and diagonal fibers that pull the two arytenoid cartilages directly together, closing the back portion of the glottis that the lateral cricoarytenoid can’t fully reach.
- Thyroarytenoid: This muscle runs within the vocal fold itself. It stiffens the fold and slightly draws it inward, which changes how the fold vibrates and helps fine-tune pitch.
- Oblique arytenoid: Diagonal fibers that cross from one arytenoid to the other, reinforcing closure. Some of these fibers extend upward into the fold above the vocal cords, helping seal the larynx entrance during swallowing.
These muscles don’t just slam the vocal cords shut. They coordinate in subtle, precisely timed patterns depending on whether you’re speaking, swallowing, coughing, or holding your breath. During speech, the closing muscles bring the folds together gently enough that air pressure can still push them apart in a controlled cycle. During swallowing, they contract forcefully to create a tight seal.
How Your Brain Sends the Signal
The command center for vocal cord movement sits in a cluster of nerve cells called the nucleus ambiguus, located in the medulla, the lowest part of your brainstem. This region houses the motor neurons responsible for swallowing and speech. If both sides of the nucleus ambiguus are destroyed, the larynx becomes completely paralyzed, and the inability to move the vocal cords during breathing can be fatal.
From the nucleus ambiguus, signals travel down the vagus nerve, which splits into two key branches before reaching the larynx. The recurrent laryngeal nerve (RLN) takes a long, looping path down into the chest and back up along the trachea before entering the larynx from below. It controls every intrinsic laryngeal muscle except one. The superior laryngeal nerve takes a shorter route and powers the cricothyroid muscle, which stretches and tenses the vocal folds to raise pitch.
The RLN’s unusually long path through the neck and chest makes it vulnerable to injury during thyroid surgery, heart surgery, or from tumors pressing on it. Surgical trauma to the RLN, superior laryngeal nerve, or vagus nerve is the single most common cause of bilateral vocal cord paralysis, accounting for about 44% of cases. Cancers cause another 17%, prolonged breathing tubes about 15%, and neurological diseases like ALS or Guillain-Barré syndrome about 12%.
What Happens During Breathing
Every breath you take involves your vocal cords opening wider. As you inhale, the PCA muscle activates and pulls the folds apart to let air pass freely into your lungs. During quiet exhaling, the folds drift slightly closer together but stay open. This cycle repeats roughly 12 to 20 times per minute at rest without any conscious effort.
During exercise, the larynx adjusts by abducting the vocal folds and the structures above them even further, maximizing the size of the airway to accommodate heavier airflow. This widening is driven by stronger PCA activation as your brainstem’s respiratory centers demand more oxygen. In some people, the larynx paradoxically narrows during intense exercise instead of opening, a condition called exercise-induced laryngeal obstruction that can mimic asthma.
What Happens During Speech
Speaking requires a precisely coordinated cycle of closing and opening that repeats extraordinarily fast. First, the closing muscles bring the vocal folds together. Air pressure builds below them until it’s strong enough to push them apart. In a healthy voice, this phonation threshold pressure is around 2.4 to 3.0 centimeters of water pressure at conversational volume. People with vocal fold polyps or other lesions need roughly twice as much pressure, which is why speaking feels effortful when the vocal cords are swollen or damaged.
Once air pushes through the folds, the gap between them narrows, which speeds up the airflow. This faster airflow creates a drop in pressure (sometimes called the Bernoulli effect) that helps draw the folds back together. Combined with the natural elastic recoil of the vocal fold tissue, this restarts the cycle. The result is rapid vibration: men’s vocal folds vibrate around 115 times per second in normal conversation, with a range of about 90 to 500 Hz. Women’s vocal folds vibrate around 200 times per second, ranging from 150 to 1,000 Hz.
Importantly, the muscles aren’t firing individually for each vibration cycle. They set the position and tension of the folds, and then airflow and tissue elasticity sustain the oscillation. It’s similar to how your lips buzz when you blow a raspberry: you position them, and the air does the rest.
Protective Reflexes That Force Closure
Your vocal cords also snap shut involuntarily when something threatens to enter your airway. This laryngeal adductor reflex is triggered by touch or chemical irritation on the lining of the larynx. Sensory receptors detect the stimulus and send a signal up the internal branch of the superior laryngeal nerve to the brainstem. The signal passes through the nucleus tractus solitarius to the nucleus ambiguus, which fires back through the recurrent laryngeal nerve, producing a rapid bilateral contraction of the muscles within the vocal folds. This reflex is fast, involuntary, and active even while you’re speaking or singing.
Coughing involves a more complex sequence. First, the vocal folds close tightly during a compression phase, trapping air below them while chest muscles build pressure. Then the folds burst open for the expulsive phase, releasing a high-speed blast of air. The opening velocity during cough expulsion is significantly faster than the closing speed during the compression phase. After the blast, the vocal folds close again in more than half of moderate to hard coughs, likely to rebuild pressure for a second pulse if needed.
During swallowing, closure is even more thorough. The vocal folds press together, the structures above them (the false vocal folds and the epiglottis) fold down to create a second and third layer of protection, and the entire larynx lifts upward and forward. This multi-layered seal keeps food and liquid out of your airway dozens of times a day without you thinking about it.
When the System Breaks Down
Because the nerve pathway from the brainstem to the larynx is long and passes through several vulnerable areas, many things can disrupt it. The most common cause of vocal cord paralysis is surgical injury, particularly during thyroid, neck, or chest operations where the recurrent laryngeal nerve runs close to the surgical field. Tumors in the neck, chest, or base of the skull can compress the nerve. Viral infections occasionally inflame it. Neurological diseases that attack motor neurons or nerve insulation can paralyze the vocal cords as part of a broader pattern of muscle failure.
When one vocal cord is paralyzed, it typically stays in a partially open position. The working cord can still move to meet it, but the seal is incomplete, producing a breathy, weak voice and sometimes causing choking on liquids. When both cords are paralyzed in a closed or near-closed position, the airway narrows dangerously. When both are paralyzed open, breathing is fine but the voice is severely impaired and aspiration risk is high. About 12% of bilateral vocal cord paralysis cases have no identifiable cause.