The Wonders of the Tongue — Its Muscles with Motor and Sensory Nerve Innervations.
Figure 1: A sagittal section of the nose mouth, pharynx, and larynx. Notice how the tongue sits in the oral cavity and the bones and muscles surrounding it. From: Henry Gray. Anatomy of the Human Body.
Introduction
Have you ever wondered how your tongue worked? If you think about it, it is quite complicated and intricated on how all these muscles come together so that you can move your tongue around and change its shape. It is also fascinating to learn about its general sensory nerves which give you the sensation of temperature, pressure and touch, and the special sensory nerves of the tongue, which include taste.
So how does it work? What muscles are used and what nerves are responsible for it? Let us find out!
Before we go, we need to know some important terminology. Why? Because a lot of muscles and nerves you are about to see includes the word glossus or lingual, which makes much sense once it has been described.
Glōssa means tongue or language in Greek, hence the relation with glossus.
Hypo, from Greek, means under or beneath. It is a very useful prefix!
Hippo from híppos is derived from the Greek word meaning horse, don’t get these two confused. We see it in Hippocampus, which means horse + sea monster and which describes the hippocampus in the brain (as it looks like a sea horse).
Lingua to lingualis / lingual, which means tongue, language or speech in Latin. This is where we get language or a logo (although logos is Greek for word or reason).
Disclaimer: These beautiful pictures and drawings are from the lovely textbook of Gray’s Anatomy for Student, and the fantastic drawings are from the Atlas of Human Anatomy from F. Netter, MD. If you are interested, please buy the textbooks and do not download/share/print illegally. To the copyright holders, please do let me know if these pictures are unlawfully being used as I shall be taking them down immediately. No copyright infringement is intended. I shall also use the old school 1918 Gray’s Anatomy drawings (which mind you is fantastic and pretty cool!) as I believe they are now public domain.
What’s on the tongue?
Let us start by looking at what is on the tongue and what it is made out of. The top layer is covered with stratified squamous epithelium where it is keratinised on the top but not on the underside. The surface is covered with 4 different types of papillae, and these are the: circumvallate, foliate, fungiform and filiform. The circumvallate are the least numerous (8 to 12) but are the largest and are present at the back of the tongue. They are large, circular in shape and generally are in a single row. The foliate are found on the lateral side of the tongue and have a ridge-like in shape. The fungiform, as the name suggests, looks like a mushroom shape-like papillae and are mostly found on the dorsal side of the tongue. They are scattered irregularly and sparingly. All three of these papillae are involved with taste. Only the filiform do not contain taste buds and are identified as more keratinised than the others. These are numerous and are actively involved with abrasion. They have a cone shape with numerous filamentous processes almost brush-like.
Figure 2: The mouth cavity. The cheeks have been slit transversely, and the tongue pulled forward. From: Henry Gray. Anatomy of the Human Body.
Figure 3: A much more updated and modern view of the dorsal of the tongue. From: Netter FH. Atlas of Human Anatomy.
Figure 4: Circumvallate papilla in vertical section, showing the arrangement of the taste-buds and nerves. From: Henry Gray. Anatomy of the Human Body.
Figure 5: Section of a fungiform papilla. This is the reason why they get their name ‘mushroom-like’. From: Henry Gray. Anatomy of the Human Body.
Figure 6: A filiform papilla, remember they do not contain taste buds. From: Henry Gray. Anatomy of the Human Body.
Figure 7: A close-up view of the different papillae. From: Netter FH. Atlas of Human Anatomy.
Figure 8: Semi-diagrammatic view of a portion of the mucous membrane of the tongue. Two fungiform papillæ are shown. Notice how some of the filiform papillae the epithelial prolongations stand erect and others are spread out. From: Henry Gray. Anatomy of the Human Body.
Muscles
The tongue lies inside the oral cavity where its origin takes part from the floor of the mouth by the mylohyoid and geniohyoid muscle of which these attaches to the hyoid and mandible bone.
Figure 9: An anterior and inferior view of the muscles that make the floor of the oral cavity. From: Netter FH. Atlas of Human Anatomy.
Figure 10: A posterior and superior view of the muscles that make the floor of the oral cavity, notice the nerve and the glands. From: Netter FH. Atlas of Human Anatomy.
Figure 11: A lateral view of the tongue, notice how it is divided by 2/3 and 1/3, which will become important when talking about nerve innervations. From: Drake RL et al. Gray’s Anatomy for Student.
There are two muscle groups for the tongue, the intrinsic and extrinsic muscle groups. The intrinsic muscles are responsible for the precise articulatory movement of the tongue, which is to change the shape and are used exclusively during speech. The extrinsic muscles move the tongue as a whole and change the position of the tongue or the location such as during mastication.
The tongue itself is divided into 2 sections. There is the oral part which is the anterior 2/3 which lies in the oral cavity proper and a pharyngeal part which is the posterior 1/3 of the tongue which lies in the oropharynx area.
The intrinsic muscles
The intrinsic muscles are supplied by the hypoglossal nerve (CV XII), which enables the motor movement of the muscles. Notice there is a mid-line septum where both the intrinsic muscles lie on both sides of it.
The superior longitudinal muscle runs along the length of the tongue towards the tip. Its function is to elevate, assist in retraction and bringing the tongue back into the oral cavity.
The inferior longitudinal muscle lies deeper within the tongue and has a similar function in deviating the tongue to the side and pulls the tip of the tongue downwards inferiorly. This muscle also assists in the retraction of the tongue.
The transverse muscle allows narrowing of the tongue, and as the name suggests, the muscle runs from the left to the right.
Finally, there are the vertical muscle fibres which pull the tongue down towards the floor of the mouth.
Figure 12: The Coronal section of the tongue, showing intrinsic muscles. From: Henry Gray. Anatomy of the Human Body.
Figure 13: A more extensive description of the extrinsic and intrinsic muscles of the tongue. From: Drake RL et al. Gray’s Anatomy for Student.
The extrinsic muscles
These contain the palatoglossus, styloglossus, hyoglossus and genioglossus. They are all attached to the tongue (remember glossus) and have their origin attached to their name (palato, stylo, hyo and genio).
Palatoglossus (P), from the palate towards the tongue forms lateral arches situated at the back and lateral aspects of the throat. It is more closely associated with the soft palate both in situation and function.
Styloglossus (S), the shortest and smallest of the three styloid muscles. It comes from the styloid process and goes towards the tongue. It retracts the tongue as it pulls back and also elevates the posterior aspects of the tongue.
Hyoglossus (H), is more like a sheet running from the body of the hyoid bone up towards the tongue. It depresses the tongue.
Genioglossus (G), triangular looking, it forms the bulk of the tongue and is a single muscle even if it is shown as three. Used to poke the tongue out from the fibres that lie most anteriorly. The central part depresses the tongue.
Figure 14: The extrinsic muscles of the tongue from a lateral view. From: Henry Gray. Anatomy of the Human Body.
Figure 15: A lateral view of the cavity box, notice the muscles that make the floor of the mouth and the extrinsic muscles. From: Netter FH. Atlas of Human Anatomy.
Nerve innervation
The tongue innervation can be a bit complicated due to the sensory component of the tongue as it is divided into anterior 2/3 and posterior 1/3. These areas are supplied by different nerves. Some nerves hitchhike on other nerves, which can be a bit confusing.
Motor innervation
All supplied by the hypoglossal nerve (CV XII), that is intrinsic and most extrinsic muscles except the palatoglossus, which is supplied by the vagus (CV X). Motor innervation is the ability to move skeletal muscles through the usage of nerves. These are efferent nerves which carries information out from the Central Nervous System (CNS).
Sensory supply
There are two main class of sensory input: general (touch, temperature and pressure) and special sensation (taste). Figure 16 and 17 demonstrates the sensory supply. These are afferent nerves carrying information to the CNS.
Anterior 2/3 General: supplied by the trigeminal nerve (CN V), however, the trigeminal nerve has three branches: ophthalmic (CN V1), maxillary (CN V2) and mandibular (CN V3). Hence the name Trigeminal, tri = three, geminus = twin. Out of those three branches, the mandibular (CN V3) branch gives rise to another smaller branch called the lingual nerve, which supplies the anterior 2/3 of the tongue (and that is general sensation). To sum it up: trigeminal nerve (CN V), branch to mandibular nerve (CN V3), branch to the lingual nerve which supplies the general sensation of the 2/3 anterior of the tongue.
Anterior 2/3 Special: supplied by the facial nerve (CN VII) from a branch called the chorda tympani. The chorda tympani hitchhike onto the lingual nerve to get to the oral cavity. Hitchhiking nerves means they are sharing a common path. During surgeries as seen in the Journal of Anatomy paper ‘Surgical anatomy and pathology of the middle ear’ damage to the chorda tympani can occur and patients may lose the sensation of taste to a certain degree.
“During any middle ear surgery, the surgeon is confronted with the course of the chorda tympani. In chronic otitis media and, especially, in cases of cholesteatoma, the chorda tympani sometimes has to be ‘sacrificed’ (cut through) to gain higher safety for full eradication of the disease (i.e. if the chorda tympani is embedded in the cholesteatoma). Sometimes, especially in the endaural approach towards the stapes in otosclerosis surgery, the chorda tympani has to be stretched and moved aside to gain better access to the middle ear and especially to the ossicular chain. Although the chorda is flexible and hence moving it temporarily aside is possible, this stretching may result in taste disturbances. Fortunately, these tend to disappear after a short time, as the sense of taste is transmitted by a total of six nerves on both sides of the mouth (nervi VII, IX, X), which after a while recoup the full sense. Still, the chorda may be accidentally injured, for example when removing parts of the bony ear canal in the dorsal aspect. Likewise, drying up of the nerve fibers resulting from the steady hot light of the surgical microscope or simply by contacting the bare nerve with a thick suction tube may harm the nerve function.” From: Luers JC and Hüttenbrink KB (2016).
Posterior 1/3 General and Special: both are supplied by the glossopharyngeal nerve (CV IX).
Figure 16: A lateral view of the cavity box, notice the nerve innervation of the muscles. From: Drake RL et al. Gray’s Anatomy for Student.
Figure 17: Notice the nerve innervation of the muscles and the comparison between motor and sensory innervation. From: Drake RL et al. Gray’s Anatomy for Student.
Published 10th September 2019. Last reviewed 1st December 2021.
Reference
Drake RL, Vogl AW, Mitchell AWM. Gray’s Anatomy for Student. 3rd ed. Philadelphia: Churchill Livingston Elsevier; 2015. ISBN: 978-0-7020-5131-9.
Henry Gray. Anatomy of the Human Body. 12th ed. Philadelphia: Lea & Febiger; 1918. Thoroughly revised and re-edited by Warren H. Lewis. Accessed September 3, 2019.
Luers JC, Hüttenbrink KB. Surgical anatomy and pathology of the middle ear. J Anat. 2016;228(2): 338-353. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4718166/.
Mike Kenning. The Tongue. Teach Me Anatomy website. https://teachmeanatomy.info/head/muscles/tongue/. Update September 14, 2018. Accessed August 11, 2019.
Netter FH. Atlas of Human Anatomy. 6th ed. Philadelphia: Saunders Elsevier; 2014. ISBN: 978-1-4557-0418-7.
