Nerve and blood supply of the tongue

Muscles

The strength and mobility of the tongue are supported by its paired muscles, which are grouped as either intrinsic or extrinsic. 

The intrinsic muscles are placed completely within the bulk of the tongue. They are the superior longitudinal, inferior longitudinal, transverse, and vertical muscles.

The extrinsic muscles originate outside of the tongue and inside the oral cavity, and insert into the tongue itself. They are the genioglossus, hyoglossus, styloglossus, and palatoglossus muscles.

Mucosa

The lingual mucosa has complex sensory innervation. Aside from the ability for general sensory reception, it has special sensory components that detect taste and are presented within the lingual papillae. Hundreds of papillae are diffusely distributed all over the oral part of the superior surface of the tongue. 

There are 4 types of lingual papillae. They differ by their histological profile and sensory ability:

• Filiform papillae – are the smallest and most numerous papillae distributed over the anterior two-thirds of the tongue, parallel to the terminal sulcus, and transverse at the apex. The name originates from the Latin word “filum” which means “wire” and so their name perfectly reflects their thin and elongated shape. 
• Fungiform papillae – the name of the structure fits their mushroom-like shape. They are spread all over the superior lingual surface, but their highest concentration is at the apex and margins of the tongue.
• Vallate papillae – the largest papillae, whose number ranges from 8 to 12. They have a cylindrical shape and are characteristically aligned in a V form anterior and parallel to the terminal sulcus of the tongue. 
• Foliate papillae – these linear folds of the lingual mucosa present at the lateral edges of the posterior one-third of the tongue. These are poorly developed in humans and their taste buds degenerate in childhood.

All lingual papillae except for the filiform contain taste buds, which are special sensory receptors for taste.

Arteries

The muscles of the tongue are supplied by the lingual artery, a branch of the external carotid artery. It branches off from it in the neck at the level of the greater horn of the hyoid bone.

Then, it courses upwards, loops down, and continues forward with the hyoglossus muscle through the oropharyngeal triangle, that is the space bound by the superior pharyngeal constrictor, middle pharyngeal constrictor, and mylohyoid muscles. After this, it courses forward between the genioglossus and hyoglossus muscles to finally reach the tip of the tongue.

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On its way, the artery provides the dorsal lingual arteries which supply the root of the tongue, and the deep lingual arteries which supply the body of the tongue. Along with the muscles and mucosa of the tongue, the lingual artery also supplies the mucosa of the of the oral cavity floor, sublingual gland, and the gingiva. 

Veins

Venous drainage of the tongue is enabled with the paired deep lingual veins and a single dorsal lingual vein. The dorsal lingual vein follows the path of the dorsal lingual arteries. On the other hand, the deep lingual veins originate from the tip of the tongue, continue posteriorly to the lingual frenulum by accompanying the deep lingual arteries, and then join the sublingual vein.

The sublingual vein then either drains directly into the internal jugular vein in the neck, or they merge and form the lingual vein which then tributes to the internal jugular vein near the beginning of the lingual artery.

Hypoglossal nerve

The hypoglossal nerve (CN IX) innervates all the tongue muscles except for the palatoglossus. This nerve exits the skull through the hypoglossal canal, and courses straight downward to the point just below the angle of the mandible.

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From there it courses forward, first crossing the external carotid artery and then crossing the loop of the lingual artery. The hypoglossal nerve then follows the hyoglossus muscle though the oropharyngeal triangle and finally reaches the tongue.

Vagus nerve

The vagus nerve (CN X) innervates the palatoglossus muscle. The vagus nerve does so indirectly, via branches of the pharyngeal plexus. This plexus is placed on the surface of the middle pharyngeal constrictor muscle and is formed by the:

• Sensory pharyngeal branches of the glossopharyngeal nerve (CN IX)
• Motor pharyngeal branch of the vagus nerve
• Sympathetic fibers from the superior cervical ganglion

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Glossopharyngeal nerve

It carries general sensory information from the of mucosa of the posterior one-third of the tongue, and special sensory information from the vallate papillae. The glossopharyngeal nerve (CN IX) leaves the skull through the jugular foramen. It then descends down the lateral surface of the stylopharyngeus muscle and passes through the oropharyngeal triangle. The nerve then reaches the oropharynx, from where it enters the tongue just inferiorly to the styloglossus and hyoglossus muscles.

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Lingual nerve

This is a branch of the mandibular component of the trigeminal nerve (CN V3). It carries general sensory information from the anterior two-thirds of the tongue.After originating in the infratemporal fossa, it passes through the oropharyngeal triangle and reaches the floor of the oral cavity. By continuing anteriorly across the floor, the lingual nerve reaches the submandibular duct, and after looping around it, it ascends into the tongue.

Facial nerve

The facial nerve (CN VII) carries special sensory taste information from the anterior two-thirds of the tongue. These fibers leave the tongue as a part of the lingual nerve, but at the infratemporal fossa they join the chorda tympani. Chorda tympani is a branch of the facial nerve, which then continues to the central nervous system.

Tongue innervation summary

• All the muscles are innervated by the hypoglossal nerve (CN XII) except for the palatoglossus muscle
• The palatoglossus muscle is innervated by the vagus nerve (CN X)
• The posterior one-third of the tongue is innervated by the glossopharyngeal nerve (CN IX) which carries both general sensory information from mucosa and special sensory information from the vallate papillae.
• The anterior two-thirds of the tongue have double sensory innervation. The lingual nerve, a branch of the mandibular nerve (CN V3) carries general sensory information (temperature and touch) from this surface. Special sensory taste information is carried by the fibers of the facial nerve (CN VII) which leave the tongue as a part of the lingual nerve, but at the infratemporal fossa they join the chorda tympani (a branch of the facial nerve).