M01.02.018 The Tongue

The tongue is a muscular structure located on the floor of the oral cavity, serving as the primary organ of taste and playing a vital role in swallowing and speech.

This guide will cover:

Structure: Intrinsic and extrinsic muscles
Innervation: Motor and sensory nerves
Vasculature and lymphatics
Embryological development
Clinical relevance: Key conditions such as tongue-tie

1. Structure of the Tongue

1.1 Intrinsic Muscles

Definition: Muscles entirely within the tongue.
Functions: Change tongue shape (e.g., rolling), speech, eating, and swallowing.

Intrinsic Muscle	Orientation	Function	Innervation
Superior Longitudinal	Runs longitudinally	Shortens tongue, curls tip	Hypoglossal nerve (CN XII)
Inferior Longitudinal	Runs longitudinally	Shortens tongue, curls tip	Hypoglossal nerve (CN XII)
Transverse	Runs horizontally	Narrows and elongates tongue	Hypoglossal nerve (CN XII)
Vertical	Runs vertically	Flattens and broadens tongue	Hypoglossal nerve (CN XII)

1.2 Extrinsic Muscles

Definition: Muscles that originate outside the tongue and attach to it.
Function: Facilitate gross movements (protrusion, elevation, depression).

Extrinsic Muscle	Origin	Insertion	Function	Innervation
Genioglossus	Mandibular symphysis	Entire tongue, hyoid bone	Protrusion, depression	Hypoglossal nerve (CN XII)
Hyoglossus	Hyoid bone	Lateral tongue	Depression, retraction	Hypoglossal nerve (CN XII)
Styloglossus	Styloid process of temporal bone	Lateral tongue	Retraction, elevation	Hypoglossal nerve (CN XII)
Palatoglossus	Palatine aponeurosis	Broad tongue insertion	Elevation of posterior tongue	Vagus nerve (CN X)

2. Innervation of the Tongue

2.1 Motor Innervation

Hypoglossal Nerve (CN XII): Supplies all intrinsic and extrinsic muscles except palatoglossus.
Vagus Nerve (CN X): Supplies palatoglossus.

2.2 Sensory and Taste Innervation

Region	General Sensation	Taste
Anterior 2/3	Lingual nerve (CN V3)	Chorda tympani (CN VII)
Posterior 1/3	Glossopharyngeal nerve (CN IX)	Glossopharyngeal nerve (CN IX)

3. Vasculature and Lymphatics

3.1 Blood Supply

Arterial Supply:
- Lingual artery (branch of external carotid artery).
- Contributions from the tonsillar branch of the facial artery.
Venous Drainage:
- Lingual vein draining into the internal jugular vein.

3.2 Lymphatic Drainage

Region	Lymph Nodes
Anterior two-thirds	Submental, submandibular → deep cervical
Posterior one-third	Directly into deep cervical nodes

4. Embryological Development

The tongue develops from branchial arches 1–4:
- First arch: General sensation by CN V.
- Second arch: Overgrown, but taste from CN VII remains.
- Third arch: Supplies posterior third via CN IX.
- The fourth arch: Contributes to the posterior-most part via CN X.

Key Structures

Median Sulcus: Fusion line of the tongue during development.
Sulcus Terminalis: Boundary between anterior 2/3 and posterior 1/3.
Foramen Cecum: Remnant of the thyroglossal duct.

5. Clinical Relevance

5.1 Tongue-Tie (Ankyloglossia)

Cause: Shortened or thickened frenulum.
Impact:
- Impaired breastfeeding in infants.
- Speech difficulties in severe cases.
Management: Surgical correction (frenotomy).

Points to Remember

The tongue is divided into anterior 2/3 and posterior 1/3 based on sensory and taste innervation.
Motor innervation is predominantly via the hypoglossal nerve (CN XII), except for the palatoglossus (vagus nerve).
The lingual artery is the main blood supply, while lymphatic drainage varies by region.
Developmental anomalies like tongue-tie can impact feeding and speech.

Bibliography

TeachMeSeries Ltd. Anatomy of the Tongue (2024).
Netter, F. Atlas of Human Anatomy.