Cranial Nerve # 12: Hypoglossal Nerve

Description and Physiology

The hypoglossal nerve is chiefly a motor nerve responsible for innervating the muscles of the tongue.  This cranial nerve is also responsible for the articulation of speech and the act of swallowing. The hypoglossal nerve is found beneath the tongue as the word roots imply.  It originates from the lateral medulla of the brain.  The hypoglossal nerve innervates all of the muscles of the tongue except for the palatoglossus, which is controlled by the vagus nerve.  The three muscles of the tongue controlled by the hypoglossal nerve  are the genioglossus muscle, the hypoglossus muscle, and styloglossus muscle.  The genioglossus muscle pushes the tongue out and can depress the center of the tongue.  The hypoglossus muscle is responsible for depressing the entire tongue.  The styloglossus muscle is the muscle that retracts and elevates the tongue.

Hypoglossal Nerve Lesions

Nerve lesions on the hypoglossal nerve can produce wasting on the opposite side of the tongue and also fasciculations, or muscle twitches.  When the tongue is pushed out of the mouth it deviates toward the side where the lesion exists.  For a central lesion the tongue deviates away from the central lesion. This is the result of a low motor neuron lesion. Weakness of the tongue is displayed as a slurring of speech. The tongue may feel “thick”, “heavy”, or “clumsy.”

To test the function of the nerve, a person is asked to poke out his/her ttongue. If there is a loss of function on one side, the tongue will point toward the affected side

Literature Cited: 

Gailard, F., Jones, J. 2005-2010. Cranial nerves. Radiopaedia.org; [updated 2011, cited 2012 Apr 18]. Available from: http://radiopaedia.org/articles/cranial_nerves

Hypoglossal nerve [Internet]. 2012. The Free Dictionary; [cited 2012 May 1]. Available from:http://medical-dictionary.thefreedictionary.com/hypoglossal+nerve

Right hypoglossal nerve palsy. 2012. Youtube; [updated 2012 Apr 30, cited 2012 May 6]. Available from: http://www.youtube.com/watch?v=HABYt4FrgpA

Thackery, G. 1997. The cranial nerves. Loyola University of Medical Education Network; [updated 1997 Aug 28, cited 2012 May 1]. Available from: http://www.stritch.luc.edu/lumen/MedEd/GrossAnatomy/h_n/cn/cn1/mainframe.htm

Thomas, H. 2010. Cranial nerve lesions. Patient.co.uk; [updated 2010 May 27, cited 2012 May 2]. Available from: http://www.patient.co.uk/doctor/Cranial-Nerve-Lesions.htm

http://www.livestrong.com/article/138620-list-cranial-nerves-assessed-during-neurological-assessment/?utm_source=popslideshow&utm_medium=a1

http://www.nursingcenter.com/library/JournalArticle.asp?Article_ID=930500

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