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

Table 1

Classification of the efferent peripheral nerves innervating striated musculature based on embryological and anatomical findings. All cranial nerves have a nucleus within the brainstem and receive mesenchymal contributions from neural crest cells. The cranial nerves can be subdivided into 3 groups. CSEpr cranial nerves innervate striated muscle derived from preotic somites. CSEpo cranial nerves innervate striated musculature from postotic somites, while CBE cranial nerves innervate striated muscle developing from somitomeres (head mesoderm). Spinal nerves have a nucleus within the spinal cord and muscles of somitic origin. Trunk Mesenchyme also forms from the mesodermal layer. The transitional nerve (accessory proper) has a nucleus within the spinal cord, innervates muscle derived from somites, and has mesenchymal elements that form from neural crest cells, thus making it a unique peripheral nerve. It is important to note that the eleventh crania nerve is represented entirely by the laryngopalatopharyngeal motor (LPP) formerly the cranial root of the accessory.

	Target muscle(s)	Nucleus location	Mesoderm	Neural crest	Classisfication
Cranial Nerves
III	Extraocular eye m.’s	Brainstem	Preotic Somite	YES	CSEpr
IV	Superior Oblique m	Brainstem	Preotic Somite	YES	CSEpr
V	Muscles of Mastication	Brainstem	L.P.M.	YES	CBE
VI	Lateral Rectus m	Brainstem	Preotic Somite	YES	CSEpr
VII	Facial Expression/2nd Jaw	Brainstem	L.P.M.	YES	CBE
IX	Pharynx	Brainstem	L.P.M.	YES	CBE
X	Int Laryn. Palate, Pharynx	Brainstem	Occipital Somites	YES	CSEpo
XI-Palatopharyngeal	Pharynx	Brainstem	Occipital Somites	YES	CSEpo
XII	Tongue m.’s	Brainstem	Occipital Somites	YES	CSEpo
Transitional neve
XI-accessory proper	SCM and trapezius	Spinal cord	Cervical somites	YES	TSE
Spinal Nerves
31 human	Respective myotome	Spinal cord	Somite	NO	GSE