A valve

Sipping espresso in the Cafe, I hear the background noise of the espresso grinder mingling with the murmur of voices. The couple next to me are chatting in Japanese, drinking coffee and downing a pastry. I don’t understand a word, but still I can hear that each person’s larynx is functioning well. 

The larynx is a valve, designed to control the flow of food, air and sound. Each person takes a sip of coffee, swallows, breathes in and then engages in conversation. Liquids and solids are separated from the air each individual breathes, then directed down the esophagus. Air is directed between the vocal cords into his and her lungs. The air is put to use again to make sound on its way back out. The larynx does all of this work, all very rapidly and all rather precisely.

Thus, the larynx is basically a talented valve, with three main functions:

• regulate breathing,
• create sound and
• keep food and liquids out of the lungs.

Of course, we have all seen someone blast his friend with drink when he rushes his larynx and tries to swallow and talk simultaneously. It helps to have a microsecond or two between functions.

As the young man beside me swallows his coffee, I see the bulge of his “Adam’s apple” or medically speaking, the thyroid cartilage, moving up and down in his neck. The soft thyroid cartilage enlarges when exposed to testosterone, perhaps partly for evolutionary mating reasons. The net external effect is that it protrudes visibly. On the inside testosterone thickens and elongates the vocal cords. The longer and thicker they end up, the lower the notes they are capable of producing. The thyroid cartilage sits above and articulates with the cricoid cartilage. Below the larynx is the windpipe or trachea, which you can feel in some people with thin necks. Above the Adam’s Apple, the hyoid bone, which helps suspend the larynx in the neck.

The hyoid bone (top yellow) is connected to the tongue and jaw muscles above and the thyroid cartilage below. The thyroid cartilage (central blue) is also known as the Adams Apple and protects the vocal cords, which are attached on the backside in the middle. The cricoid cartilage (lower green) is a complete ring supporting the base of the larynx.

For hoarseness, we are generally interested in the vocal cords, located posterior to the thyroid cartilage. The vocal cords can easily be visualized from above, by passing a device into the pharynx. A rigid endoscope views the larynx from the back of the mouth.

A rigid endoscope is passed through the mouth to visualize the vocal cords. It is difficult to say much of anything other than /i/ while the examiner holds your tongue, but it does provide a very clear picture of the vocal cords. Most people need some topical anesthesia in order to keep from gagging during this examination.

A flexible endoscope views the larynx from the back of the nose. 

A flexible endoscope is passed through the nose. At the back of the nose, it is angled inferiorly, then advanced into the pharynx to view the vocal cords.

The space inside the throat above the larynx is the pharynx. It is surrounded by muscles and the hyoid bone. Changing the shape and size of the pharynx alters resonance.

The pharynx is the space around the larynx, here relaxed and open (yellow arrows). Right: The pharynx is being squeezed to reduce the size of the chamber (blue arrows), selectively amplifying highpitched sounds through resonance.

Technically the larynx has two cartilages that maintain its shape (thyroid and cricoid). A softer cartilage acts as a diverting valve during swallowing (epiglottis). Two smaller cartilages open and close the vocal cords (arytenoids) and some miniscule cartilages sit on the arytenoids seeming to act as a dam to prevent residual liquids in the piriform sinuses from entering the airway.

The soft curved cartilage in the middle of the photo is the epiglottis (blue arrow). Its base is attached to the back of the thyroid cartilage just above the vocal cords (the inverted V in the middle of the picture). The epiglottis comes in many different shapes and it folds over when swallowing to cover the vocal cords. The corniculate & cuneiform cartilages rest on top of the arytenoid cartilage (yellow arrows).

Left: The arytenoids (approximate location colored yellow) in an open (abducted position). The round tracheal rings are partially visible in the distance beyond the vocal cords. Right: The arytenoids bringing the vocal cords together (adducted position) to make sound. 

The front of the thyroid cartilage is triangular or tentlike in shape, suspending and protecting the vocal cords, with the Adam’s apple representing the apex. Inside, the airway is essentially a round tube with the vocal cords narrowing the airway, acting as a valve, technically – the glottis. The vocal cords narrow the opening to a triangle. During exhaling (breathing out), the vocal cords narrow the triangle to keep some backpressure in the lungs. During phonation, the vocal cords come almost completely together to form a narrow slit. Air passing between the vocal cords sets them vibrating and generates sound.

Left: The vocal cords form a triangle when breathing in. Middle: The triangle narrows when breathing out. Right: The vocal cords line up parallel to form a slit during sound production.

There are 10 internal laryngeal muscles, vocal ligaments and some glands for lubrication. This is all covered with delicate, nearly translucent mucosa, tinted pink when viewed from far away by the blood flowing beneath it. All of this sounds complicated, but the machinery of the voice box is elegantly simple, with each component serving a specific purpose. Let’s take a closer look at the muscles, or if they are deep beneath the surface, we will visualize their action by their effects in the photos.

Summary

What the purpose of the larynx?

• Be a valve

What does this valve control?

• allow air in (breathing)
• control airflow out (sound production)
• separate food from air (lung protection during swallowing)

What laryngeal anatomy can one see?

• joint movement
• muscle function