Anatomy and Physiology of the Tongue

Nerve Supply of the Tongue: Innervation by Cranial Nerves and Their Functional Roles

The tongue is a highly specialized muscular organ essential for speech, taste, mastication, and swallowing. Its innervation is complex, involving multiple cranial nerves that serve distinct sensory and motor functions.

Motor Innervation

The tongue's motor control is primarily governed by the hypoglossal nerve (CN XII), which innervates all intrinsic and extrinsic muscles except the palatoglossus.

• Intrinsic muscles: Responsible for fine movements such as shaping the tongue.
• Extrinsic muscles: Control gross movements, including protrusion and retraction.

Sensory Innervation

General Sensation

General sensory innervation of the tongue is divided into anterior and posterior regions:

• Anterior two-thirds: Supplied by the lingual nerve (branch of CN V3, mandibular division of the trigeminal nerve).
• Posterior one-third: Innervated by the glossopharyngeal nerve (CN IX).

Taste Sensation

Taste perception is mediated by different cranial nerves:

• Anterior two-thirds: Taste fibers travel via the chorda tympani (branch of CN VII, facial nerve).
• Posterior one-third: Taste sensation is carried by the glossopharyngeal nerve (CN IX).
• Epiglottis and pharynx: Taste fibers are transmitted via the vagus nerve (CN X).

Clinical Significance

Damage to these nerves can result in various dysfunctions:

• Hypoglossal nerve palsy: Leads to tongue deviation towards the affected side.
• Glossopharyngeal nerve damage: Impairs taste and sensation in the posterior tongue.
• Facial nerve injury: Affects taste perception in the anterior tongue.

Conclusion

The tongue's innervation is a complex interplay of cranial nerves, each contributing to its diverse functions. Understanding this anatomy is crucial for diagnosing neurological disorders affecting speech, taste, and swallowing.