Tongue
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Direct answer
The tongue is a muscular organ concerned with taste, mastication, deglutition and speech. The sulcus terminalis divides it into an anterior two-thirds (oral part) and a posterior third (pharyngeal part), and this division is mirrored in its nerve supply — general sensation and taste from the anterior two-thirds travel in the lingual nerve and chorda tympani, while both modalities of the posterior third run in the glossopharyngeal nerve.
What you must remember
- Parts: anterior two-thirds and posterior third separated by the sulcus terminalis, at the apex of which lies the foramen caecum, the embryological origin of the thyroid.
- Intrinsic muscles: superior and inferior longitudinal, transverse and vertical — all alter the shape of the tongue and are supplied by the hypoglossal nerve.
- Extrinsic muscles: genioglossus (protrudes the tongue), hyoglossus (depresses and retracts), styloglossus (retracts and curls up the sides) — all by the hypoglossal nerve; palatoglossus (elevates the posterior tongue) is supplied by the vagus through the pharyngeal plexus.
- Nerve supply of the anterior two-thirds: general sensation — lingual branch of the mandibular nerve; taste — chorda tympani branch of the facial nerve.
- Nerve supply of the posterior third and vallate papillae: glossopharyngeal nerve for both sensation and taste; the vallecula, in front of the epiglottis, is supplied by the internal laryngeal branch of the vagus.
- Blood supply and drainage: lingual artery; venous drainage to the internal jugular vein. Lymph from the tip goes to submental nodes, the margins to submandibular nodes, and the posterior third to deep cervical nodes on both sides.
- Clinical: in unilateral hypoglossal palsy the tongue deviates towards the affected side on protrusion (genioglossus pushes the tongue forward); carcinoma of the posterior third spreads bilaterally because its lymphatics cross the midline.
Common confusion
Students exchange the taste and general sensation fibres of the anterior two-thirds — the lingual nerve carries ordinary sensation while the chorda tympani, hitch-hiking on it, carries taste (and parasympathetic fibres to the submandibular ganglion). A second trap is the nerve of the palatoglossus: it is the only "tongue" muscle supplied by the vagus, not the hypoglossal nerve. The vallate papillae also trip examinees — lying just anterior to the sulcus terminalis, they are supplied by the glossopharyngeal nerve, not the chorda tympani.
Exam-focused takeaway
In theory, cover the parts, papillae, intrinsic and extrinsic muscles with actions and nerve supply, and lymphatic drainage with its surgical importance. In viva, expect the nerve supply of each region including the vallecula, the effect of hypoglossal nerve lesions, and the developmental origin of the thyroid from the foramen caecum. In practicals, identify the extrinsic muscles on a prosection, point out the sulcus terminalis and vallate papillae, and inspect the tongue for deviation, wasting and fasciculation.
Frequently asked questions
What is the nerve supply of the anterior two-thirds of the tongue?
General sensation is carried by the lingual nerve, a branch of the mandibular division of the trigeminal nerve. Taste travels in the chorda tympani, a branch of the facial nerve that joins the lingual nerve.
Which nerve supplies the posterior third?
The glossopharyngeal nerve carries both general sensation and taste from the posterior third, including the vallate papillae. Sensation from the vallecula comes from the internal laryngeal nerve.
Which is the only tongue muscle supplied by the vagus nerve?
The palatoglossus, supplied through the pharyngeal plexus. All the other extrinsic muscles and the intrinsic muscles are supplied by the hypoglossal nerve.
Why does the tongue deviate in hypoglossal palsy?
The paired genioglossus muscles protrude the tongue by pulling it forward and towards the opposite side. When one side is paralysed, the intact muscle pushes the tongue towards the paralysed side.