How the larynx protects the airway during swallowing
During a swallow the larynx protects the airway: the vocal cords (folds of tissue that vibrate to make sound) adduct to close the glottis, the narrow gap between them.
Remember
Adducting the vocal cords to close the glottis is the most direct barrier to aspiration (food or liquid entering the airway) during a swallow. Raising the larynx and narrowing the laryngeal inlet, the opening at the top of the larynx, add to the protection.
Memory aid
close, narrow, lift
Use it to recall the three protective movements of a swallow: close the cords, narrow the inlet, lift the larynx.
In a safe swallow, food and drink do not enter the airway but are directed towards the oesophagus (the food pipe). If food or fluid does get into the airway, that is called aspiration. Keeping food and fluid out of the airway is arguably the most important job of the larynx (the voice box, in the front of the neck), and the larynx does this with three movements working together.
First, the vocal cords adduct, which means that they move together. This closes the glottis, the narrow gap between the cords that leads down into the trachea, and it forms the most direct barrier at the level of the cords. The opposite movement is abduction: it moves the cords apart and opens the glottis for breathing.
Second, the aryepiglottic muscles contract to narrow the laryngeal inlet, the opening at the top of the larynx, and to fold the epiglottis (the small cartilage flap at the top of the larynx) over it. At the same time, stylopharyngeus (a muscle of the throat) and the suprahyoid muscles (the group above the hyoid, a small U-shaped bone in the neck) pull the larynx upwards, which helps to close the inlet.
Together these give a series of barriers, one at the cords and one above them, rather than relying on a single movement. Lowering the larynx works against airway protection. The infrahyoid muscles (the group below the hyoid bone) lower the larynx, whereas swallowing raises it.
Do not confuse this with a cough, in which the cords also adduct first but then suddenly snap open to blow air out and clear material that is already in the airway.
Key facts
- Glottis
- the narrow gap between the vocal cords, closed by adduction of the cords during a swallow.
- Opening the glottis
- abduction opens it for breathing, and the posterior cricoarytenoids are the only muscles that abduct (open) the cords.
- Laryngeal inlet
- the aryepiglottic muscles contract to narrow the inlet and fold the epiglottis over it.
- Raising the larynx
- stylopharyngeus and the suprahyoid muscles pull the larynx upwards, which helps to close the inlet.
- Experiments in cats
- closure of the glottis was the main protection against aspiration, with elevation of the larynx assisting.
- Cough
- the cords adduct first and then snap open, so opening clears the airway while closing protects it.
Exam traps
- Contraction of the posterior cricoarytenoids does not close the glottis. They abduct the cords and leave the glottis open, and laryngeal elevation does not make up for that, because a safe swallow requires vocal cord adduction.
- Lowering the larynx with the infrahyoid muscles does not protect the airway, because swallowing raises the larynx and raising it helps to close the inlet.
- Relaxing the aryepiglottic muscles does not seal the laryngeal inlet, because these muscles contract during swallowing to narrow it.
Read the full notes
Tested in 8 SimpleMed+ questions
Practice it in Head and Neck, with the answer and a full explanation after every question.
Practice these questions