Focused anatomy guide
Hypoglossal nerve
In this guide
The tongue is a muscular organ involved in speech, swallowing, and moving food. Its precise movements depend largely on the hypoglossal nerve, also called cranial nerve XII or CN XII. It carries motor signals from the brain to most of the tongue muscles.
What is the hypoglossal nerve?
The hypoglossal nerve is the twelfth pair of cranial nerves. It is primarily a motor nerve. It supplies the intrinsic muscles of the tongue and three of its four extrinsic muscles. The palatoglossus is the exception: it receives motor supply through the vagal pathway via the pharyngeal plexus.
Origin and course
CN XII begins at the hypoglossal nucleus in the medulla oblongata. Its rootlets emerge from the front of the medulla between the pyramid and the olive. The nerve then passes through the hypoglossal canal at the base of the skull and travels into the upper neck.
In the neck, it runs towards the tongue and passes close to muscles including the hyoglossus. It distributes branches to the muscles that shape, elevate, depress, protrude, and retract the tongue.
Classification and functional components
The hypoglossal nerve is classified as a somatic motor nerve. Its fibres carry commands from the central nervous system to skeletal muscles. It does not provide general sensation from the tongue; sensory information travels through other cranial nerve pathways.
Motor signals
Commands reach the tongue muscles so they can contract in coordinated patterns.
Tongue shape
Intrinsic muscles alter the tongue’s length, width, thickness, and surface shape.
Coordination
Movement supports clear speech, swallowing, and the handling of food.
The hypoglossal nucleus
The hypoglossal nucleus is a group of motor nerve cells in the medulla. Signals from the motor areas of the cerebral cortex reach it through corticonuclear pathways. The muscles that protrude the tongue receive especially important input from the opposite cerebral hemisphere.
Functions
The four intrinsic muscles change the tongue’s form. The longitudinal muscles shorten and curve it, while the transverse and vertical muscles narrow, broaden, flatten, or deepen it. These adjustments help the tongue make fine movements.
The genioglossus moves the tongue forward and forms much of its bulk. The hyoglossus helps pull it down and back, while the styloglossus helps draw it back and raise it. Together, these muscles support the varied movements needed for speaking and swallowing.
When the nerve is affected
Injury or disease involving CN XII or its nucleus can weaken tongue movement. When a lower motor pathway is affected, the tongue may drift towards the weaker side when protruded. Weakness, wasting, or small involuntary muscle movements may also occur.
Possible causes depend on the location and nature of the problem. They can include compression, inflammation, vascular injury, trauma, and disorders affecting the brainstem or wider nervous system. A new change in speech, swallowing, or tongue movement needs assessment by a qualified healthcare professional.
A useful distinction
This page explains anatomy and common neurological patterns for learning. It cannot determine the cause of an individual symptom or replace clinical assessment.
Summary
The hypoglossal nerve is CN XII and is mainly a motor nerve. It begins in the medulla, leaves the skull through the hypoglossal canal, and reaches the tongue. It controls the intrinsic muscles and most extrinsic muscles, enabling the tongue to change shape and move in the directions needed for speech and swallowing.
References
Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012
Blumenfeld, Neuroanatomy Through Clinical Cases, Sinauer Associates, 2002
Standring, Gray’s Anatomy, Elsevier Churchill Livingstone.