同: CN VI, 外転神経

WordNet

any bundle of nerve fibers running to various organs and tissues of the body (同)nervus
control of your emotions; "this kind of tension is not good for my nerves"

PrepTutorEJDIC

〈C〉『神経』 / 〈C〉《複数形で》『神経過敏』,いらだち / 〈U〉『勇気』,度胸(courage) / 〈U〉《時にa ~》厚かましさ,ずぶとさ;無礼 / 〈C〉葉脈;(昆虫の)翅脈(しみゃく) / 〈人,特に自分〉‘に'力を与える,‘を'元気づける

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/09/02 15:27:53」(JST)

wiki en

The abducens nerve or abducent nerve (the sixth cranial nerve, also called the sixth nerve or simply CNVI) is a somatic efferent nerve that, in humans, controls the movement of a single muscle, the lateral rectus muscle of the eye.

Structure

The Clivus

The abducens nerve leaves the brainstem at the junction of the pons and the medulla, medial to the facial nerve. In order to reach the eye, it runs upward (superiorly) and then bends forward (anteriorly).

The nerve enters the subarachnoid space when it emerges from the brainstem. It runs upward between the pons and the clivus, and then pierces the dura mater to run between the dura and the skull through Dorello's canal. At the tip of the petrous temporal bone it makes a sharp turn forward to enter the cavernous sinus. In the cavernous sinus it runs alongside the internal carotid artery. It then enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye.

The long course of the abducens nerve between the brainstem and the eye makes it vulnerable to injury at many levels. For example, fractures of the petrous temporal bone can selectively damage the nerve, as can aneurysms of the intracavernous carotid artery. Mass lesions that push the brainstem downward can damage the nerve by stretching it between the point where it emerges from the pons and the point where it hooks over the petrous temporal bone.

Nucleus

Axial section of the Brainstem (Pons) at the level of the Facial Colliculus

The abducens nucleus is located in the pons, on the floor of the fourth ventricle, at the level of the facial colliculus. Axons from the facial nerve loop around the abducens nucleus, creating a slight bulge (the facial colliculus) that is visible on the dorsal surface of the floor of the fourth ventricle. The abducens nucleus is close to the midline, like the other motor nuclei that control eye movements (the oculomotor and trochlear nuclei).

Motor axons leaving the abducens nucleus run ventrally and caudally through the pons. They pass lateral to the corticospinal tract (which runs longitudinally through the pons at this level) before exiting the brainstem at the pontomedullary junction.

The central anatomy of the sixth nerve predicts (correctly) that infarcts affecting the dorsal pons at the level of the abducens nucleus can also affect the facial nerve, producing an ipsilateral facial palsy together with a lateral rectus palsy. The anatomy also predicts (correctly) that infarcts involving the ventral pons can affect the sixth nerve and the corticospinal tract simultaneously, producing a lateral rectus palsy associated with a contralateral hemiparesis. These rare syndromes are of interest primarily as useful summaries of the anatomy of the brainstem.

Development

The human abducens nerve is derived from the basal plate of the embryonic pons.

In animals

The abducens nerve controls the movement of a single muscle, the lateral rectus muscle of the eye. In most other mammals it also innervates the musculus retractor bulbi, which can retract the eye for protection. Homologous abducens nerves are found in all vertebrates except lampreys and hagfishes.

Function

The abducens nerve carries axons of type GSE, general somatic efferent, which innervate skeletal muscle of the lateral rectus.

Clinical significance

Examination

Complete interruption of the peripheral sixth nerve causes diplopia (double vision), due to the unopposed action of the medial rectus muscle. The affected eye is pulled medially. In order to see without double vision patients will rotate their heads so that both eyes are toward the temple. Partial damage to the sixth nerve causes weak or incomplete abduction of the affected eye. The diplopia is worse on attempted lateral gaze, as would be expected (since the lateral gaze muscle is impaired).

Peripheral lesions

Complete interruption of the peripheral sixth nerve causes diplopia (double vision), due to the unopposed action of the medial rectus muscle. The affected eye is pulled medially. In order to see without double vision, patients will turn their heads sideways so that both eyes are looking sideways. On formal testing, the affected eye cannot abduct past the midline – it cannot look sideways, toward the temple. Partial damage to the sixth nerve causes weak or incomplete abduction of the affected eye. The diplopia is worse on attempted lateral gaze, as would be expected (since the lateral gaze muscle is impaired).

Peripheral sixth nerve damage can be caused by tumors, aneurysms, or fractures – anything that directly compresses or stretches the nerve. Other processes that can damage the sixth nerve include strokes (infarctions), demyelination, infections (e.g. meningitis), cavernous sinus diseases and various neuropathies. Perhaps the most common overall cause of sixth nerve impairment is diabetic neuropathy. Iatrogenic injury is also known to occur, with the abducens nerve being the most commonly injured cranial nerve in halo orthosis placement.^[1] The resultant palsy is identified through loss of lateral gaze after application of the orthosis.

Rare causes of isolated sixth nerve damage include Wernicke-Korsakoff syndrome and Tolosa-Hunt syndrome. Wernicke-Korsakoff syndrome is caused by thiamine deficiency, classically due to alcoholism. The characteristic ocular abnormalities are nystagmus and lateral rectus weakness. Tolosa-Hunt syndrome is an idiopathic granulomatous disease that causes painful oculomotor (especially sixth nerve) palsies.

Indirect damage to the sixth nerve can be caused by any process (brain tumor, hydrocephalus, pseudotumor cerebri, hemorrhage, edema) that exerts downward pressure on the brainstem, causing the nerve to stretch along the clivus. This type of traction injury can affect either side first. A right-sided brain tumor can produce either a right-sided or a left-sided sixth nerve palsy as an initial sign. Thus a right-sided sixth nerve palsy does not necessarily imply a right-sided cause. Sixth nerve palsies are infamous as “false localizing signs.” Neurological signs are described as “false localizing” if they reflect dysfunction distant or remote from the expected anatomical location of pathology. Isolated sixth nerve palsies in children are assumed to be due to brain tumors until proven otherwise.

Nuclear lesions

Damage to the abducens nucleus does not produce an isolated sixth nerve palsy, but rather a horizontal gaze palsy that affects both eyes simultaneously. The abducens nucleus contains two types of cells: motor neurons that control the lateral rectus muscle on the same side, and interneurons that cross the midline and connect to the contralateral oculomotor nucleus (which controls the medial rectus muscle of the opposite eye). In normal vision, lateral movement of one eye (lateral rectus muscle) is precisely coupled to medial movement of the other eye (medial rectus muscle), so that both eyes remain fixed on the same object.

The control of conjugate gaze is mediated in the brainstem by the medial longitudinal fasciculus (MLF), a nerve tract that connects the three extraocular motor nuclei (abducens, trochlear and oculomotor) into a single functional unit. Lesions of the abducens nucleus and the MLF produce observable sixth nerve problems, most notably internuclear ophthalmoplegia (INO).

Supranuclear lesions

The sixth nerve is one of the final common pathways for numerous cortical systems that control eye movement in general. Cortical control of eye movement (saccades, smooth pursuit, accommodation) involves conjugate gaze, not unilateral eye movement.

Tuberculosis

15-40% of people with tuberculosis have some resulting cranial nerve deficit. The sixth nerve is the most commonly affected cranial nerve in immunocompetent people with tuberculosis.^{[citation needed]}

History

Etymology

The Latin name for the sixth cranial nerve is nervus abducens. The Terminologia Anatomica officially recognizes two different English translations: abducent nerve and abducens nerve.^[2] Either term is correct.

“Abducens” is more common in recent literature, while “abducent” predominates in the older literature. The United States National Library of Medicine uses “abducens nerve” in its Medical Subject Heading (MeSH) vocabulary to index the vast MEDLINE and PubMed biomedical databases. The 39th edition of Gray’s Anatomy (2005) also prefers “abducens nerve.”^[3]

References

^ http://www.orthobullets.com/spine/2019/halo-orthosis-immobilization
^ Federative Committee on Anatomical Terminology. Terminologia Anatomica. Thieme, 1998
^ Standring S (ed.) Gray’s Anatomy, 39th edition. Elsevier Churchill Livingstone, 2005

Blumenfeld H. Neuroanatomy Through Clinical Cases. Sinauer Associates, 2002
Brodal A. Neurological Anatomy in Relation to Clinical Medicine, 3rd ed. Oxford University Press, 1981
Brodal P. The Central Nervous System, 3rded. Oxford University Press, 2004
Butler AB, Hodos W. Comparative Vertebrate Neuroanatomy, 2nd ed. Wiley-Interscience, 2005
Carpenter MB. Core Text of Neuroanatomy, 4th ed. Williams & Wilkins, 1991.
Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science, 4th ed. McGraw-Hill, 2000
Martin JH. Neuroanatomy Text and Atlas, 3rd ed. McGraw-Hill, 2003.
Patten J. Neurological Differential Diagnosis, 2nd ed. Springer, 1996.
Victor, M, Ropper, AH. Adam’s and Victor’s Principles of Neurology, 7th ed. McGraw-Hill, 2001.
Wilson-Pauwels L, Akesson EJ, Stewart PA. Cranial Nerves: Anatomy and Clinical Comments. Decker, 1998.

Additional images

Dura mater and its processes exposed by removing part of the right half of the skull, and the brain.
Superficial dissection of brain-stem. Ventral view.
Hind- and mid-brains; postero-lateral view.
Figure showing the mode of innervation of the Recti medialis and lateralis of the eye.
Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.
Cerebrum.Inferior view.Deep dissection

External links

hier-541 at NeuroNames
MedEd at Loyola GrossAnatomy/h_n/cn/cn1/cn6.htm
Animations of extraocular cranial nerve and muscle function and damage (University of Liverpool)
cranialnerves at The Anatomy Lesson by Wesley Norman (Georgetown University) (VI)

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 複視の概要 overview of diplopia
2. 小児における第6脳神経（外転神経）麻痺 sixth cranial nerve abducens nerve palsy in children
3. 視覚変化が認められた小児患者に対するアプローチ approach to the pediatric patient with vision change
4. 小児における水平斜視の原因 causes of horizontal strabismus in children
5. 特発性頭蓋内圧亢進症（偽脳腫瘍）：臨床的特徴および診断 idiopathic intracranial hypertension pseudotumor cerebri clinical features and diagnosis

English Journal

Vanishing calcification associated with a spontaneous ventral spinal cerebrospinal fluid leak.

Schievink WI1, Ross L2, Prasad RS3, Maya MM3.
Cephalalgia : an international journal of headache.Cephalalgia.2016 Jan 20. pii: 0333102416628468. [Epub ahead of print]
BACKGROUND: Some patients with spontaneous intracranial hypotension have a ventral spinal cerebrospinal fluid (CSF) leak and these CSF leaks may be associated with calcified disk herniations. Identifying these calcifications is helpful in directing treatment. We report here the unusual case of a pat
PMID 26792915

Ruptured Pseudoaneurysm after Gamma Knife Surgery for Vestibular Schwannoma.

Murakami M1, Kawarabuki K, Inoue Y, Ohta T.
Neurologia medico-chirurgica.Neurol Med Chir (Tokyo).2016 Jan 15;56(1):38-42. doi: 10.2176/nmc.cr.2015-0034. Epub 2015 Dec 11.
Ruptured aneurysms of anterior inferior cerebellar artery (AICA) after radiotherapy for vestibular schwannoma (VS) are rare, and no definite treatment has been established for distal AICA pseudoaneurysms. We describe a 61-year-old man who underwent Gamma Knife surgery (GKS) for left VS. Follow-up ma
PMID 26667081

Identification of cranial nerves around trigeminal schwannomas using diffusion tensor tractography: a technical note and report of 3 cases.

Wei PH1, Qi ZG2, Chen G1, Li MC1, Liang JT1, Guo HC1, Bao YH3, Hao Q4.
Acta neurochirurgica.Acta Neurochir (Wien).2016 Jan 6. [Epub ahead of print]
BACKGROUND: There are no large series studies identifying the locations of cranial nerves (CNs) around trigeminal schwannomas (TSs); however, surgically induced cranial neuropathies are commonly observed after surgeries to remove TSs. In this study, we preoperatively identified the location of CNs n
PMID 26733128

Japanese Journal

視線追跡装置を用いた健常者と外転神経麻痺患者の衝動性眼球運動速度の比較 (第70回日本弱視斜視学会(3)) -- (ポスターセッション)

眼科臨床紀要 8(7), 488-491, 2015
NAID 40020536411

メビウス症候群の顔面神経麻痺に対する，遊離広背筋移植による動的再建術において，動力源となる神経の選択に難渋した1例

日本マイクロサージャリー学会会誌 28(3), 134-139, 2015
NAID 130005099286

Use of Oculomotor Testing for Identifying the Site of Cerebellar or Brainstem Damage in Two Vertigo Cases

耳鼻咽喉科臨床　補冊 141(0), 10-11, 2015
NAID 130005077972

Related Pictures

★リンクテーブル★

リンク元	「sixth cranial nerve」「abducent nerve」「cranial nerve VI」「nervus abducens」
拡張検索	「abducens nerve disease」「abducens nerve palsy」
関連記事	「abducens」「nerve」

「sixth cranial nerve」

Abducent nerve
	The path of the Abducens nerve
	Inferior view of the human brain, with the cranial nerves labelled.
Details
From	abducens nucleus
Identifiers
Latin	nervus abducens
MeSH	A08.800.800.120.030
TA	A14.2.01.098
FMA	50867
	Anatomical terms of neuroanatomy [edit on Wikidata]

　　[★]

第VI脳神経、第6脳神経、第六脳神経

関: abducens nerve、abducent nerve、cranial nerve VI

「abducent nerve」

　　[★]

外転神経

関: abducens、abducens nerve、cranial nerve VI、nervus abducens、sixth cranial nerve

「cranial nerve VI」

　　[★]

第VI脳神経

関: abducens nerve、abducent nerve、sixth cranial nerve

「nervus abducens」

　　[★]