Organ
Hypoglossal nucleus
Medullary motor neurons for tongue movement
High-yield
Nuclear or fascicular damage produces tongue weakness on the same side. On protrusion, the tongue usually deviates toward that side; denervation may later produce wasting and fasciculations. Supranuclear weakness is often milder and follows a different, variable pattern.
Overview
Each hypoglossal nucleus is a column of motor neurons close to the medullary midline. In the open medulla it lies beneath the hypoglossal trigone on the fourth-ventricle floor; caudally it continues beside the central canal. Its axons pass forward through the medulla and emerge between the pyramid and olive to form CN XII.
Reference facts
- Location
- Dorsomedial medulla, beneath the hypoglossal trigone rostrally and close to the central canal caudally
- Parts
- A longitudinal somatic motor column spanning open and closed medullary levels
- Relations
- Outgoing fibers traverse the medial medulla before emerging in the preolivary sulcus; neighboring long tracts explain combined deficits in larger lesions
- Function
- Motor output to intrinsic tongue muscles, genioglossus, hyoglossus and styloglossus; palatoglossus uses the vagal motor pathway
Clinical correlation
The nucleus or its outgoing fibers may be involved in medial medullary lesions. Associated injury to the pyramid and medial lemniscus can add weakness and loss of vibration or position sense on the opposite side of the body. An isolated nuclear lesion does not produce the whole syndrome.
Frequently asked questions
Where is the hypoglossal nucleus located?
The hypoglossal nucleus lies dorsomedial medulla, beneath the hypoglossal trigone rostrally and close to the central canal caudally.
What does the hypoglossal nucleus do?
Motor output to intrinsic tongue muscles, genioglossus, hyoglossus and styloglossus; palatoglossus uses the vagal motor pathway.
What are the parts of the hypoglossal nucleus?
A longitudinal somatic motor column spanning open and closed medullary levels.