Anatomy of the Tongue

Anatomy of the Tongue

🌬 What is the Tongue?

The tongue is a solid, conical, muscular organ located partly in the oral cavity (floor of the mouth) and partly in the pharynx.

👅 Functions of the Tongue:

• Primary organ of taste.
• Aids in mastication (chewing).
• Essential for deglutition (swallowing).
• Crucial for speech.
• Helps in moistening the lips.
• Used in gestures and facial expressions.

✨ Parts of the Tongue

The tongue has several distinct anatomical parts:

• Tip:

The pointed, anterior-most part that touches the incisors.

• Base:

The posterior part directed towards the oropharynx, formed by the posterior one-third of the tongue.

Relations:

The mucous membrane of the base reflects onto the epiglottis, forming folds.

1. Median Glossoepiglottic Fold: In the midline.

2. Lateral Glossoepiglottic Folds: On either side.

3. Valleculae: Two depressions, one on each side of the median fold, located between the tongue base and the epiglottis.

• Dorsum:

The convex upper surface, covered by mucous membrane. It is divided by a V-shaped groove called the Sulcus Terminalis.

Sulcus Terminalis divides the dorsum into:

1. Anterior Two-Thirds (Oral/Presulcal Part): Located in the oral cavity.

2. Posterior One-Third (Pharyngeal/Postsulcal Part): Located in the oropharynx.

Foramen Cecum: A central depression at the apex of the V-shaped Sulcus Terminalis.

• Inferior Surface:

The undersurface, facing the floor of the mouth. Unlike the dorsum, its mucous membrane is devoid of papillae.

Frenulum Linguae: A median fold connecting the tongue to the floor of the mouth.

Sublingual Papillae: Small eminences on either side of the frenulum, where the submandibular duct opens into the oral cavity.

Plica Fimbriata: Fimbriated folds that pass upwards and medially on each side of the frenulum.

Profunda Lingua Vein: Runs between the frenulum and the plica fimbriata.

• Lateral Margins:

The sides of the tongue, covered with mucous membrane. The Palatoglossal Arch attaches to the margin at the junction of the anterior two-thirds and posterior one-third.

• Root:

The part attached to the floor of the mouth, extending from the symphysis menti to the hyoid bone, formed by the lower fibers of the genioglossus muscle.

🧱 Structure and Surface Anatomy

The tongue is primarily composed of striated muscle fibers, along with mucous membrane, mucous glands, lymphoid tissue, fat, and fibrous tissue.

🔬 Mucous Membrane:

• The tongue is covered by a stratified squamous epithelium.

• Its character differs between the anterior and posterior parts:

  • Anterior Two-Thirds: Mucous membrane is firmly adherent to underlying muscles (via lamina propria) and is covered with numerous papillae.

  • Posterior One-Third: Mucous membrane is thicker, separated from underlying muscle by a loose submucous coat. It is devoid of papillae but contains aggregates of lymphoid follicles called the Lingual Tonsils. Lingual tonsils form part of Waldeyer's Ring (a ring of lymphoid tissue in the pharynx).

🦠 Papillae of the Tongue:

Papillae are projections of the lamina propria covered by mucous membrane, found on the dorsum of the anterior two-thirds of the tongue.

There are four types:

1. Vallate (Circumvallate) Papillae:

   • Largest type, 8-12 in number.
   • Arranged in a single V-shaped row immediately in front of and parallel to the Sulcus Terminalis.

2. Fungiform Papillae:

   • Smaller, rounded, reddish elevations.
   • Located mainly along the sides and tip of the tongue.

3. Foliate Papillae:

   • 3-4 vertical mucous folds along the lateral margins of the tongue, just in front of the Sulcus Terminalis.

4. Filiform Papillae:

   • Most numerous and smallest type.
   • Tiny conical projections covering the entire anterior two-thirds of the dorsum.
   • Arranged in V-shaped rows parallel to the Sulcus Terminalis (transverse near the apex).
   • Crucially, these are DEVOID of taste buds.

👅 Taste Buds

• Taste buds are modified epithelial cells arranged in spherical masses within the epithelium.

• Location of Taste Buds (Not just on the tongue!):

  • Dorsum of the tongue (all papillae types except filiform).
  • Mucous membrane of the Soft Palate.
  • Palatoglossal Arches.
  • Posterior surface of the Epiglottis.
  • Posterior wall of the Oropharynx.

• Structure: Composed of sensory (gustatory receptor) cells and supporting cells. Each opens via a taste pore on the epithelial surface, with gustatory hairs projecting through. Base is penetrated by gustatory nerve fibers.

• Taste Sensations & Distribution:

  • Sweet: Appreciated at the tip.
  • Salt: Appreciated at the tip and sides.
  • Sour: Appreciated along the sides.
  • Bitter: Appreciated at the posterior one-third (base).

💪 Muscles of the Tongue

The tongue is divided into two symmetrical halves by a median fibrous septum.

Its muscles are striated and arranged in two groups:

• Extrinsic Muscles: Originate outside the tongue and insert into it. Alter the POSITION of the tongue.

  • Genioglossus, Hyoglossus, Chondroglossus, Styloglossus, Palatoglossus.

• Intrinsic Muscles: Confined entirely within the tongue. Alter the SHAPE of the tongue.

  • Superior Longitudinal, Inferior Longitudinal, Transversus Linguae, Verticalis Linguae.

• (Note: A detailed discussion on the origin, insertion, nerve supply, and action of each muscle will be covered in a future post, including the important relations of the hyoglossus muscle).

Nerve Supply of Tongue:

It's divided into Motor and Sensory supply.

• Motor Supply:

  • Somatomotor (to muscles):

    • All extrinsic and intrinsic muscles are supplied by the Hypoglossal Nerve (CN XII).
    • EXCEPTION: The Palatoglossus muscle is supplied by the cranial part of the Accessory Nerve (CN XI) via the Pharyngeal Plexus.

  • Secretomotor (to glands):

    • Originates from the Superior Salivatory Nucleus -> passes via the Facial Nerve (CN VII) -> Chorda Tympani nerve -> joins the Lingual Nerve.

  • Vasomotor (to vessels):

    • Derived from sympathetic nerves around the Lingual Artery.
    • Convey postganglionic fibers from the Superior Cervical Ganglion of the Sympathetic Trunk.

• Sensory Supply: Different for anterior 2/3 and posterior 1/3 due to different embryonic origins.

  • Anterior Two-Thirds (Develops from 1st Pharyngeal Arch):

    • General Sensation (touch, pain, temperature): Supplied by the Lingual Nerve (a branch of the Mandibular division of the Trigeminal Nerve - CN V3).

    • Special Sensation (Taste): Supplied by the Chorda Tympani Nerve (a branch of the Facial Nerve - CN VII).

  • Posterior One-Third (Develops from 2nd and 3rd Pharyngeal Arches):

    • General Sensation AND Special Sensation (Taste): Both supplied by the Glossopharyngeal Nerve (CN IX).

  • Valleculae: General and Special Sensation supplied by the Internal Laryngeal Branch of the Superior Laryngeal Nerve (a branch of the Vagus Nerve - CN X).

🩸 Blood Supply of Tongue:

• Arterial Supply:

  • Chief artery: Lingual Artery (a branch of the External Carotid Artery).
  • Branches of the Lingual Artery: Dorsal Linguae (supplies posterior part), Arteria Profunda Linguae (deep artery, supplies rest of the tongue).
  • Other contributors: Ascending Palatine and Tonsillar branches of the Facial Artery, Ascending Pharyngeal Artery (also a branch of the External Carotid).

• Venous Drainage:

  • Veins are arranged in superficial and deep sets.
  • Ultimately, both sets drain into the Internal Jugular Vein.
  • Superficial veins (draining tip/undersurface) pass with the hypoglossal nerve.
  • Deep veins (draining dorsum) accompany the lingual artery deep to the hyoglossus muscle.

🦠 Lymphatic Drainage of Tongue:

This is complex and highly clinically significant for the spread of tongue cancer.

Lymphatics consist of intramuscular and submucosal plexuses, arranged in four main sets:

1. Apical Set: Drains the tip and frenulum.

   • Drain mainly to the Submental nodes (Level Ia, pierce mylohyoid).
   • A few vessels go directly to the Jugulo-omohyoid nodes.
   • Some may also drain to Submandibular nodes or Jugulo-digastric/Jugulo-omohyoid (deep path).

2. Marginal Set: Drains the sides of the tongue (anterior to sulcus terminalis).

   • Drain to the Submandibular nodes (Level Ib, pierce mylohyoid).
   • Also drain to the Jugulo-digastric (most common, Level II) and Jugulo-omohyoid (Level III) nodes (deep path).

3. Central Set: Drains the dorsal surface of the anterior two-thirds (in front of vallate).

   • Descend between the genioglossus muscles.
   • Drain to the Jugulo-digastric and Jugulo-omohyoid nodes (deep, often without piercing mylohyoid).
   • Some may pierce mylohyoid to drain into Submandibular nodes.

4. Dorsal (Basal) Set: Drains the posterior one-third (including vallate papillae).

   • Most vessels drain BILATERALLY to the Jugulo-digastric nodes (Level II).
   • A lesser pathway is direct drainage into the Jugulo-omohyoid nodes (Level III).