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Neurology Research International
Volume 2010, Article ID 476018, 15 pages
Review Article

Transitional Nerve: A New and Original Classification of a Peripheral Nerve Supported by the Nature of the Accessory Nerve (CN XI)

1Departments of Surgery, Oral Maxillofacial Surgery and Integrative Biosciences, Schools of Medicine and Dentistry, Oregon Health and Science University, 611 SW Campus, Room 713, Portland, OR 97239, USA
2Department of Integrative Biosciences, School of Dentistry, Oregon Health and Science University, Portland, OR 97239, USA

Received 21 August 2010; Accepted 14 November 2010

Academic Editor: T. Ben-Hur

Copyright © 2010 Brion Benninger and Jonathan McNeil. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Classically, the accessory nerve is described as having a cranial and a spinal root. Textbooks are inconsistent with regard to the modality of the spinal root of the accessory nerve. Some authors report the spinal root as general somatic efferent (GSE), while others list a special visceral efferent (SVE) modality. We investigated the comparative, anatomical, embryological, and molecular literature to determine which modality of the accessory nerve was accurate and why a discrepancy exists. We traced the origin of the incongruity to the writings of early comparative anatomists who believed the accessory nerve was either branchial or somatic depending on the origin of its target musculature. Both theories were supported entirely by empirical observations of anatomical and embryological dissections. We find ample evidence including very recent molecular experiments to show the cranial and spinal root are separate entities. Furthermore, we determined the modality of the spinal root is neither GSE or SVE, but a unique peripheral nerve with a distinct modality. We propose a new classification of the accessory nerve as a transitional nerve, which demonstrates characteristics of both spinal and cranial nerves.