The Tongue

Introduction to the Tongue: Anatomy and Gross Structure

The tongue is a muscular, mobile organ located securely within the oral cavity. It forms the floor of the mouth and the anterior wall of the oropharynx. Anatomically, the organ divides into two main parts: the anterior two-thirds, known as the oral body, and the posterior one-third, known as the pharyngeal root.

A V-shaped boundary called the sulcus terminalis separates these two regions on the dorsal surface. At the apex of this groove sits the foramen cecum, a small embryonic remnant marking the origin of the thyroid gland development. The mucosa covering the oral body is rough due to papillae, whereas the root features a nodular surface caused by the lingual tonsils. Beneath the organ, the lingual frenulum anchors the mucosal lining to the floor of the mouth, restricting excessive posterior movement.

Musculature: Intrinsic and Extrinsic Muscles

Lingual movement and shape changes rely entirely on a complex arrangement of skeletal muscles, categorized into intrinsic and extrinsic groups.

• Intrinsic muscles: Originate and insert entirely within the tongue substance. They include the superior longitudinal, inferior longitudinal, transverse, and vertical muscles. Their primary job is altering the shape of the tongue by making it shorter, longer, wider, or narrower.
• Extrinsic muscles: Originate from external bony structures outside the tongue and insert into it. They include the genioglossus, hyoglossus, styloglossus, and palatoglossus. These muscles move the entire organ in various directions, such as sticking it out, pulling it back, or depressing it.

Papillae and Taste Perception

The dorsal surface of the tongue features specialized mucosal projections called papillae. Most of these structures hold taste buds, which house the chemoreceptors responsible for gustation.

1. Fungiform papillae: Mushroom-shaped structures scattered mainly across the tip and sides of the tongue, containing multiple taste buds.
2. Circumvallate papillae: Large, dome-shaped papillae arranged in a V-row just anterior to the sulcus terminalis, surrounded by deep trenches containing serous glands of von Ebner.
3. Foliate papillae: Series of vertical folds located on the posterolateral borders of the tongue.
4. Filiform papillae: Small, cone-shaped projections covering most of the anterior surface. They contain no taste buds but provide mechanical friction to help move food around the mouth.

Innervation: Sensory and Motor Nerve Supply

Nerve supply to the tongue splits neatly between motor control, general sensation, and special taste sensation.

• Motor Innervation: All intrinsic and extrinsic muscles of the tongue receive motor supply from the hypoglossal nerve (CN XII), except for the palatoglossus, which is supplied by the pharyngeal plexus via the vagus nerve (CN X).
• General Sensory Innervation: Touch, pain, and temperature from the anterior two-thirds travel via the lingual nerve (branch of mandibular division of CN V). The posterior one-third receives general and taste sensation from the glossopharyngeal nerve (CN IX).
• Special Sensory (Taste) Innervation: Taste buds on the anterior two-thirds are innervated by the chorda tympani branch of the facial nerve (CN VII).

Blood Supply and Lymphatic Drainage

The tongue is a highly vascular organ, ensuring rapid healing of mucosal injuries and efficient systemic absorption of sublingual medications.

Arterial blood arrives primarily through the lingual artery, a direct branch of the external carotid artery. This vessel gives rise to the deep lingual artery, which supplies the anterior portion, and the dorsal lingual branches, which supply the root. Venous blood mirrors this path, draining through the deep lingual veins into the internal jugular vein via the facial and lingual veins.

Lymphatic drainage follows distinct pathways. The tip of the tongue drains into the submental lymph nodes. The rest of the anterior two-thirds drains into submandibular and deep cervical nodes. The posterior third drains directly into superior deep cervical nodes.

Functions: Mastication, Swallowing, and Speech

Beyond taste, the tongue plays an indispensable mechanical role in daily survival tasks. During mastication, the tongue constantly manipulates food between the occlusal surfaces of the teeth, shaping the chewed mass into a cohesive bolus while protecting the oral mucosa from accidental bites.

For swallowing (deglutition), the intrinsic and extrinsic muscles coordinate to press the bolus upward and backward against the hard palate, propelling it through the fauces into the pharynx.

In speech articulation, the tongue acts as an active valve and shape-shifter. By modifying the vocal tract and making contact with the teeth, alveolar ridge, and palate, it allows humans to produce distinct consonant and vowel sounds.