Muscles and taste sensation of the tongue (2024)

Intrinsic muscles

These muscles make up the inside of the tongue. Their fibers are placed in different directions, based on which they are named (i.e. transverse muscle has its fibers on the transverse plane), and their contractions define the shape of the tongue.

These muscles all work together to produce movements that are essential for mastication (chewing), speech, and deglutition (swallowing). These movements include elongating and retracting the tongue, elevating and lowering the apex of tongue and broadening and narrowing the surface of the tongue. They are all innervated by the hypoglossal nerve (CN XII).

Extrinsic muscles

Extrinsic muscles insert into the tongue, while their origins are outside of it. There are four pairs of extrinsic muscles, which include the genioglossus, hyoglossus, styloglossus, and palatoglossus.

They produce those movements of the tongue which the intrinsic muscles can't, which are protrusion, retraction/retrusion, depression and elevation of the tongue. All of them are innervated by the hypoglossal nerve (CN XII), except for the palatoglossus muscle which is innervated by the vagus nerve (CN X) via branches of the pharyngeal plexus.

To easily remember their origins, just pay attention the their names. For example, the hyoglossus muscle: hyo- suggests the origin from the hyoid bone, while the -glossus is from the Greek ‘glossa’, meaning ‘tongue’, where this muscle inserts. ‘Stylo-’ refers to the styloid process and ‘palato-’ refers to the palate. ‘Genio-’ on the other hand references the Greek ‘geneion’ for ‘chin’.

Genioglossus is a fan-shaped muscle that originates from the superior mental spine on the posterior mandibular surface. From that point, the inferior group of fibers inserts into the body of the hyoid bone, whereas the remaining fibers extend superiorly next to the entire length of the dorsum of tongue/lingual aponeurosis and blend with the intrinsic muscles. Bilateral contraction of this muscle depressesthe central part of the tongue, creates a longitudinal furrow and protrudes the tongue outside of the mouth. Unilateral contraction on the other hand will deviate the tongue contralaterally.

Hyoglossus is a quadrangular muscle that originates from the body and greater horn of the hyoid bone. It passes through the oropharyngeal triangle (a space in the neck bounded by the superior pharyngeal constrictor, middle pharyngeal constrictor and mylohyoid muscles), and inserts into the inferior/ventral parts of the lateral tongue, right between the genioglossus (laterally) and styloglossus (medially). Its function is to depress the lateral aspects of the tongue, as well as retrude/retract the tongue. By being as wide as the greater horn of the hyoid bone, the hyoglossus muscle makes up a big part of the floor of the oral cavity. The lingual artery, the main artery that supplies the lingual muscles, passes between the hyoglossus and genioglossus. Additionally, the hypoglossal nerve (CN XII) and the lingual nerve pass over its external surface on their way to the tongue. This makes the hyoglossus muscle an important clinical landmark.

The styloglossus muscle is shaped as a thin stripe which originates from the anterolateral aspect of the styloid process of the temporal bone and the nearby stylomandibular ligament. To reach the tongue and insert into posterolateral aspects, it passes through the oropharyngeal triangle. The longitudinal part of the styloglossus will then blend with fibers of the inferior longitudinal muscle, and the oblique part of the styloglossus musclewill blend with fibers of the hyoglossus muscles. By contracting, the styloglossus muscle retrudes/retracts the tongue and elevates its lateral aspects.

The palatoglossus is a bow-shaped muscle associated both with the tongue and the soft palate. It originates from the palatine aponeurosis of the soft palate and arches laterally downward to insert into the dorsum of the tongue and blends with the intrinsic muscles. This muscle coordinates the actions of the tongue and the soft palate. It elevates the root of the tongue, and constricts the isthmus of fauces. All these movements are necessary for closing the isthmus of the oropharynx and pushing the bolus from the oral cavity into the pharynx. Note that this is the only muscle of the tongue that is not innervated by the hypoglossal nerve (CN XII) like all the others. Instead, it is innervated by the vagus nerve (CN X) via branches of the pharyngeal plexus like other muscles of the soft palate.

Learn the muscles of the tongue easily with the following study unit and quiz.

Lingual papillae

The dorsal surface of the tongue is rough and covered with numerous papillae. These structures contain taste buds that themselves contain gustatory receptors for taste. There are four types of the lingual papillae: filiform, fungiform, vallate, and foliate; and all of them, except for the filiform contain taste buds.

Filiform papillae are the smallest and the most numerous. They are scattered all over the anterior two-thirds of the dorsal surface of the tongue in lines parallel to the terminal sulcus, and then transversely at the apex. They are thin and elongated, and have a purely mechanical role only, since they do not possess taste buds.

Fungiform papillae are shaped like mushrooms. They can be found all over the dorsal surface of the tongue, but their highest concentration is at the tip and margins of the tongue.

Vallate papillae are the largest. There are very few of them, precisely 8 - 12 in humans. They are shaped cylindrically and can be found only anterior to the terminal sulcus of the tongue, characteristically aligned in a V shape.

Foliate papillae are the linear folds of the tongue mucosa and are located at the edges of the posterior one-third of the tongue. They are poorly developed in humans since they degenerate in childhood. Fun fact is that the cats have foliate papillae very developed on their tongues. That's why their tongues are so rough.

Take the quiz below to test and consolidate your knowledge on the lingual papillae!

Taste buds

As previously said, taste buds contain the gustatory receptors cells which allow us to detect taste. The receptors are found within the lingual papillae, and they allow us to detect five types of taste: sweet, salty, bitter, sour, and umami.

The specific distribution of the receptors enables us to map the tongue based on types of taste, so that the apex predominantly detects sweetness, the lateral margins detect saltiness, the posterior part is for bitterness and sourness, while umami is detected equally in all parts. Most taste buds are found on the dorsal surface of the tongue, but they are also present on the soft palate, pharynx, larynx, and epiglottis.

Taste buds are located in different places within each papillae. In foliate and vallate papillae they are in the epithelium of their lateral surface, whereas in the fungiform papillae they are present in their apical epithelium. On the other hand, not all taste buds are innervated by the same nerve. The buds on the anterior two-thirds of the tongue and the soft palate are innervated by the chorda tympani, a branch of the facial nerve (CN VII). Those within the posterior one-third of the tongue (including all vallate papillae) and the pharynx are innervated by the glossopharyngeal nerve (CN IX). The vagus nerve (CN X) innervates the remaining taste buds in the larynx and epiglottis.

Histology of taste buds

Taste buds appear as round bodies that extend through the thickness of the epithelium of the lingual papillae. The epithelial surface of the bud contains an opening called a taste pore which interacts with the content of the oral cavity. In this way, the taste pore is the window that allows the bud to detect the chemical stimuli from the food present.

On the other hand, the inferior pole of the bud synapses with the corresponding sensory nerve (facial (CN VII), glossopharyngeal (CN IX), or vagus (CN X) that carries information of the chemical stimuli to the central nervous system via the gustatory pathway to be interpreted and perceived as a specific taste sensation.

There are three types of cells found within taste buds:

• Neuroepithelial cells – sensory cells that extend from the basal lamina to the taste pore. Their microvilli project into the pore and detect chemical stimuli (taste) from food. They synapse with the facial, glossopharyngeal, or vagus nerve to send taste information to the central nervous system
• Supporting cells – also extend from the basal lamina to the taste pore. They provide mechanical support to the taste bud and neuroepithelial cells
• Basal cells – line the basal lamina of the taste bud. They are short (do not reach the pore) stem cells for the neuroepithelial and basal cells.

Gustatory pathway

Since sensory pathways conduct information from the periphery (receptors) to the central nervous system, we’ll review the gustatory pathway in that direction.

When the taste buds from the anterior two-thirds of the tongue and soft palate are stimulated, the special visceral afferent fibers of the facial nerve (CN VII) receive that information and leave the oral cavity together with the lingual nerve. Then, in the infratemporal fossa, these special visceral afferent fibers emerge from the facial nerve and form the chorda tympani. The chorda tympani then relays sensory input to the otic and geniculate ganglia. Postganglionic fibers emerge from these ganglia and project to the brainstem and enter at the pontomedullary junction. Then they synapse within the rostral part of the nucleus of the solitary tract in the posteroinferior part of the medulla oblongata.

Learn everything about the gustatory pathway in a more fun and engaging way through our study unit:

When it comes to the posterior one-third of the tongue and pharynx, the special visceral afferent fibers from both the superior laryngeal nerve (branch of the vagus nerve (CN X)) and the glossopharyngeal nerve (CN IX) synapse with the inferior ganglion of the vagus nerve and the inferior ganglion of the glossopharyngeal nerve (also known as the petrosal ganglion). From the inferior ganglion, the postganglionic fibers exit and course towards the same spot as the chorda tympani (the nucleus of the solitary tract) after entering the brainstem at the rostral medulla oblongata.The fibers end within the rostral segment of the of anterior (ventral) solitary nucleus. The neurons of this nucleus send fibers that join the ipsilateral central tegmental tract, and then end within parvocellular division of the ventral posteromedial nucleus of the thalamus. The fibers exiting from the thalamus form central thalamic radiations, which pass through the posterior limb of the internal capsule. These fibers end within the primary gustatory cortical areas of the cerebral cortex, found within insula and frontal operculum.

Test your knowledge on the neural pathway of taste with the following quiz!