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Old 06-08-2011
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Anatomy Did the writers of HY Neuroanatomy forget basic anatomy?

Update: According to Wikipedia, it is an outdated description of CN XI that the book is using. While nerves innervating the intrinsic laryngeal muscles used to be considered a part of CN XI, they are now considered functionally part of CN X and simply temporary residents of the path of CN XI (hence the more contemporary name: Spinal accessory nerve, instead of just "accessory nerve"). I hope this helps anyone else who may have been caught up by that section of the book.


HY Neuroanatomy, Page 85 (cranial nerves chapter) of the most recent (4th edition) High Yield Neuroanatomy says:

XI. The Accessory Nerve (CN XI)
A. General characteristics. The accessory nerve mediates head and shoulder movement and innervates the laryngeal muscles.

It then goes on to say that it innervates the intrinsic muscles of the larynx save for the circothyroid by way of the recurrent laryngeal nerve.


...Am I missing something, or are they confusing cranial nerve XI with the vagus? In my anatomy class, we were taught that the nerve bundles that make up the inferior laryngeal nerve travel briefly with CN XI, but they arise from the vagal nuclei and they rapidly become a part of the vagus. Why is HY Neuroanatomy trying to claim otherwise?

Last edited by Tig2575; 06-08-2011 at 11:02 AM.
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Old 06-08-2011
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I agree

Actually, they're right...Bulbar CN11 fibers CROSS to CN10
Did the writers of HY Neuroanatomy forget basic anatomy?-screen-shot-2011-06-08-3.09.15-pm.png
click image to enlarge

please, check the attached file
Attached Files
File Type: pdf CN 11.pdf (514.2 KB)
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Old 06-08-2011
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As mentioned, the original "cranial" part of CN XI - the bulbar nuclear formation - is now considered a part of the vagus nerve's originating nuclei. The distinction is in the grouping of the nuclei, which is why when you consider the original CN XI cranial nuclei to be a part of the vagus nerve, CN XI is termed the "spinal accessory nerve," as it only retains the spinal nuclei.

I think the reason for this distinction lies in the embryology - CN's V, VII, IX, and X are the only nerves considered to be derivative of the branchial arches (and are the only cranial nerves with both motor and sensory components). Arches 4 and 6 are both considered to give rise to the vagus, rather than 4 giving rise to the vagus and 6 giving rise to part of the accessory nerve.
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Quote:
Originally Posted by Tig2575 View Post
As mentioned, the original "cranial" part of CN XI - the bulbar nuclear formation - is now considered a part of the vagus nerve's originating nuclei. The distinction is in the grouping of the nuclei, which is why when you consider the original CN XI cranial nuclei to be a part of the vagus nerve, CN XI is termed the "spinal accessory nerve," as it only retains the spinal nuclei.

I think the reason for this distinction lies in the embryology - CN's V, VII, IX, and X are the only nerves considered to be derivative of the branchial arches (and are the only cranial nerves with both motor and sensory components). Arches 4 and 6 are both considered to give rise to the vagus, rather than 4 giving rise to the vagus and 6 giving rise to part of the accessory nerve.
This is from the last edition of Snell - Clinical Neuroanatomy (2010)

XI Accessory
Cranial root Motor (SVE) Muscles of soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), and larynx (except cricothyroid) in branches of vagus Jugular foramen
Spinal root Motor (SVE) Sternocleidomastoid and trapezius muscles

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