Content Reviewers:Viviana Popa, MD, Andrew Horne, MSc, BSc (Hons), Leah Labranche, PhD, MSc, BSc(Hons)
The tongue is part of what makes these videos possible. Without it, we couldn’t speak! It is also what allows us to enjoy the taste of our favourite foods, and helps us get the occasional pesky bit of food out from between our teeth.
Now, the tongue is essentially a mass of muscles covered by a mucous membrane, which can contract and relax quickly, allowing the tongue to assume many shapes and positions.
This is what makes the tongue ideal for speaking by aiding sound formation. The tongue is also involved in taste via taste receptors; it pushes food into the oropharynx during swallowing; it helps with mastication by moving food closer to our teeth; and in oral cleansing.
Looking at things in more detail, the tongue takes up much more space in the mouth than you might realize. It consists of a root, a body and an apex, with the last two being highly mobile.
The root of the tongue is posterior and slightly vertical, forming the posterior one third of the tongue. It extends from the hyoid, epiglottis, and soft palate, to the mandible.
The body forms the anterior ⅔ of the tongue, and the apex of the tongue is the most anterior end of the body.
The entirety of the tongue rests on the mouth’s floor both in the oral cavity and into the oropharynx, with the apex pressing against the lower incisors.
The tongue also has two surfaces, supero-posterior and inferior, which are separated by the margin of the tongue.
The supero-posterior surface is the larger of the two and it literally represents the “top” or dorsum of the tongue. The inferior surface or “underside” rests against the floor of the mouth.
The dorsum of the tongue is characterized by a V-shaped groove called the terminal sulcus.
The sulcus divides the top of the tongue transversely into a presulcal anterior part in the oral cavity and a postsulcal posterior part situated in the oropharynx.
The V’s tip points posteriorly to something called the foramen cecum, which represents the remnant of part of the embryonic thyroglossal duct, from which the thyroid gland developed.
The dorsum also presents a central groove called the median lingual sulcus, which separates the anterior part of the tongue into a right and left division.
This area is sprinkled with numerous different types of lingual papillae. There are four main types of lingual papillae including vallate, foliate, filiform and fungiform papillae which give the tongue its rough texture.
All of these papillae contain taste-buds with the exception of the filiform papillae. First off, there are large and flat vallate papillae, which are arranged in a V-shaped row directly anterior to the terminal sulcus.
The papillae are surrounded by circular trenches, whose walls contain the actual taste buds. Second, foliate papillae are poorly developed lateral folds of lingual mucosa which are more developed in animals than humans.
They are located posteriorly, lateral to the terminal sulcus. Next, filiform papillae are scaly, conical projections covering most of the anterior ⅔ of the tongue.
Filiform papillae do not contain taste buds but they contain touch-sensitive nerve endings and they help with scraping movements that allow soft foods, like ice cream, to enter your mouth.
Fun fact: in cats, these papillae are much more developed, which helps them with grooming!
Lastly, fungiform papillae are mushroom-shaped structures located amongst the filiform papillae, especially at the apex and margins of the tongue.
The mucosa of the posterior part of the tongue, situated posterior to the terminal sulcus is thick and contributes to the anterior wall of the oropharynx.
It presents no lingual papillae, but it’s scattered with lymphoid nodules, which give it a cobblestone appearance.
These nodes are collectively known as the lingual tonsils and they are involved in the immune response to oral pathogens.
Now, the inferior surface of the tongue, or its “underside”, is the smooth surface that rests against the mouth’s floor.
It is smooth because it is covered in a thin, transparent mucous membrane which is connected to the floor of the mouth by a fold of tissue called the frenulum.
The frenulum allows free movement to the anterior part of the tongue, while also helping to anchor the tongue within the mouth.
On each side of the frenulum you can actually see a deep lingual vein and a sublingual caruncle, which is a small swelling of tissue.
The sublingual caruncles on each side contain the openings of the submandibular ducts, through which the submandibular salivary glands empty their contents into the oral cavity. Try looking for these structures on yourself, by looking in a mirror and lifting up your tongue!
Next, let’s talk about the muscles that make up our tongue. These can be divided into extrinsic and intrinsic muscles, which act independently or together to alter the position and shape of the tongue.
The four intrinsic and four extrinsic muscles in each half of the tongue are separated by the median lingual septum.
In general, the extrinsic muscles alter the position of the tongue while the intrinsic muscles alter its shape.
Let’s begin with the extrinsic muscles of the tongue which include the genioglossus, hyoglossus, styloglossus, and palatoglossus.
Their role is mainly in moving the tongue but they can help alter its shape as well. First, the genioglossus is an anterior, fan-shaped muscle that accounts for most of the tongue muscle.
It originates on the mental spine of the mandible and inserts on the dorsum of the tongue and the body of the hyoid bone.
Its main actions include tongue depression, protrusion, and contralateral deviation. Bilaterally the genioglossus muscles create a longitudinal furrow that helps during swallowing.
The hyoglossus sits posterior to the genioglossus and it originates on the body and greater horn of the hyoid bone.
It then goes on to insert on the infero-lateral part of the tongue. Its main role is in tongue depression and retrusion.
Next is the styloglossus, and as its name suggests, it originates on the distal styloid process and stylohyoid ligament.
It then inserts on the posterior sides of the tongue between the fibers of the hyoglossus muscle.