• GSE
• hypoglossal nucleus,

• Exits brain stem between the inferior olive and the medullary pyramids as a row of small fascicles of fibres
  
  
• These fascicles collate, forming the hypoglossal nerve
  
  
• Exits the cranial vault through the hypoglossal canal.
  
  
• Descends in the neck to about the level of the hyoid bone.
  
  
• Curves forward between the stylohyoid and the hyoglossus muscles to lie on the latter.
  
  
• Enters the tongue to innervate the muscles
  
  
• Joined by first and second cervical nerves, postganglionic sympathetic fibres from cervical ganglia
  

• Intrinsic muscles of the tongue
• Extrinsic muscles of the tongue except palatoglossus

Applied anatomy

Damage to the hypoglossal nerve may be due to:

• Brain stem vascular lesion (see medial medullary syndrome)
  
  
• Bulbar polio
  
  
• Brain stem or cerebellar tumors
  
  
• Mandibular and/or tongue tumors/surgery.

The symptoms are typical of lower motor neuron damage. If the damage if unilateral, the tongue always deviates toward the side of the lesion, when protruded.

Upper motor neuron lesions produce a contralateral paralysis of the tongue musculature, because the descending corticobulbar fibres cross en route to the hypoglossal nucleus.