A Journey Through the Airways
Let's review some airway anatomy.
Welcome to the anatomy activity. My name’s Olivia Davies, I’m a consultant anaesthetist at UCLH. A good knowledge of anatomy is absolutely fundamental to anyone who will be managing, and particularly, instrumenting the patient’s airway. Now I know that pure anatomy can be quite dry, so we’ve introduced a lot of clinical content to help to keep you interested. The anatomy activity will be divided into a number of topics. We’re going to be covering the nose, the mouth and pharynx, the larynx, and the trachea and bronchial tree. Please look at the resources section where you’ll find links to video demonstrations of all those topics.
So I’d like to start by talking about the larynx and the reason for that is the larynx is absolutely key in airway management, and also because it’s a really interesting and complex structure involved in phonation, coughing and straining, and it prevents aspiration of food into the airway. Now we’re going to go into a little bit more detail of the larynx. First of all, we’ll talk about the cartilages which are these large white structures. There are nine cartilages. We’ve got three unpaired cartilages– the thyroid, the cricoid cartilage, and the epiglottis. Then we’ve got three paired cartilages– the arytenoids, the corniculates, and the cuneiforms, which you can’t see quite so well on here.
Let’s go into all of that in a bit more detail. First of all to orientate you, up here we’ve got the hyoid bone which is the only bony structure in the larynx. This big shield-shaped structure is the thyroid cartilage and if I turn it around, you can see the laryngeal prominence, which is also known as the Adam’s apple, more prominent in men. Inferior to the thyroid cartilage is the cricoid cartilage. If I turn the model around, you can see that the cricoid cartilage is a complete ring of cartilage, unlike the tracheal cartilages, which are C-shaped and joined posteriorly by the trachealis muscle.
The cricoid cartilage is narrow anteriorly and wider posteriorly, and that’s why it’s referred to as being the shape of a signet ring. Below the cricoid cartilage, these are the tracheal rings. If I tend to model around, we’ve got the arytenoid cartilages, which are these triangular shaped cartilages. At the apex of the arytenoids are the corniculate colleges just on the tip and also attached to the apex of the arytenoids are the cuneiform cartilages. While we’ve got the model this way around, you can also see this flapping structure. This is the epiglottis. It’s also a cartilage and it flaps down like the lid of a bin to help prevent aspiration of food down into the airway.
Let’s talk about the more interesting structures of the larynx. Here we can see the vocal chords. The vocal chords in real life are a pearly white colour, and they’re interesting because any tube, such as an endotracheal tube, will pass through the vocal cords and you’ll need to visualise them on laryngoscopy. Here is the epiglottis and you can see it flapping down over the vocal chords and it sometimes obstructs your view on laryngoscopy. Another structure which is of clinical interest is this ligament here that runs between the cricoid cartilage and the thyroid cartilage, and it’s called the cricothyroid ligament. And that’s interesting because that is the site of emergency front neck access or cricothyroidotomy.
In a case, for example, of airway obstruction, you can access the airway through this structure. Below it you have some tracheal rings and the case where a surgeon wants to insert a tracheostomy, they’ll do that between the second and third tracheal rings. Now I’m going to talk about the muscles of the larynx. They’re essentially divided into the extrinsic and the intrinsic muscles. On this model we can’t see any of the extrinsic muscles, but they’re essentially on the outside, and all you need to know is that they elevate and depress the whole larynx. Of more interest are these intrinsic muscles which move the vocal chords. First of all, we’re going to talk about the muscles tense and relax the vocal chords.
This muscle here anteriorly runs from the cricoid cartilage to the thyroid cartilage, and it’s called the cricothyroid muscle. And the role of the cricothyroid muscle is to tense the vocal chords. So I turn the model sideways on, you can see that as that muscle tenses the whole of the thyroid cartilage hinges forward. This hinges forward, and as it hinges forward the vocal chords tense. The muscle that relaxes the vocal chords is found here. It’s called the thyroarytenoid muscle because it runs from the thyroid to the arytenoid, and as that muscle tenses, the vocal chords relax.
Next, we’re going to talk about the muscles that abduct and adduct the vocal chords, and they are called the cricoarytenoids. Firstly, on the posterior side of the model, we have the posterior cricoarytenoid. As the posterior cricoarytenoid tenses, the vocal chords abduct. That means that they open– abduct, or open. And another muscle is called the lateral cricoarytenoid, which runs from the cricoid to the arytenoid down inside of the vocal chords. And the function of that muscle is to adduct the vocal chords, or close vocal chords. As well as that, we have a couple of muscles that run between the arytenoids. We’ve got a pair of oblique arytenoids and an unpaired transverse arytenoid.
The last two muscles are those that invest in the epiglottis, and they act like a purse string to close the laryngeal aperture to prevent aspiration of food. The are called the aryepiglottic and thyroepiglottic muscles. So that’s the larynx. I do hope that you enjoy the anatomy activity and good luck.
A good knowledge of anatomy is of fundamental importance to anybody managing a patient’s airway. In this video, Dr Olivia Davies, Consultant Anaesthetist at University College London Hospitals demonstrates the anatomy of the larynx.
Descriptive anatomy can be a challenge for the most enthusiastic learner; as such this activity aims to provide you with some basic, digestible, functional anatomy relevant to your clinical practice.
Please click on the links below to access the Anatomy Activity Resources. Further video demonstrations and summaries can be found in the “See Also” and “Download” section.
• Nose
• The Trachea and Bronchial tree
In Week 2 you will be able to use the knowledge you have learned about anatomy to better understand the steps of Airway Assessment and Airway Ultrasound.
To complete this week, we are giving you the opportunity to test your knowledge on airway anatomy in our anatomy quiz. Move on to the next step to start this activity.
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