眼球運動・前庭系（MLF）

機能 / Function

水平注視の制御系。前頭眼野などの皮質指令が傍正中橋網様体(PPRF)に入り同側の外転神経核(VI)を駆動する。VI核からは外転神経が同側外直筋を支配し、核間ニューロンが内側縦束(MLF)を上行して対側の動眼神経核(III)内直筋亜核を支配することで両眼の共同水平運動を生む。前庭神経核はVI核/MLFを介して前庭動眼反射(VOR)を担う。図は左方視の経路（右方視は左右対称）。

Horizontal gaze control. Cortical commands (e.g., frontal eye field) reach the paramedian pontine reticular formation (PPRF), which drives the ipsilateral abducens nucleus (VI). VI sends the abducens nerve to the ipsilateral lateral rectus, while internuclear neurons ascend in the medial longitudinal fasciculus (MLF) to the contralateral oculomotor nucleus (III, medial rectus subnucleus), yielding conjugate horizontal gaze. The vestibular nuclei drive the vestibulo-ocular reflex via VI/MLF.

主要構造 / Key structures

• 前頭眼野（右・対側を駆動）Frontal eye field (right)
• 傍正中橋網様体（左 PPRF）Paramedian pontine reticular formation (L)
• 外転神経核（左 VI）Abducens nucleus (L)
• 左外直筋（外転）Left lateral rectus (abduction)
• 内側縦束（右 MLF）Medial longitudinal fasciculus (R)
• 動眼神経核（右 III）Oculomotor nucleus (R)
• 右内直筋（内転）Right medial rectus (adduction)
• 前庭神経核（左）Vestibular nuclei (L)

回路破綻による症状 / Symptoms of disruption

MLF障害=核間性眼筋麻痺(INO): 患側眼の内転障害＋外転眼の解離性眼振(輻輳は保たれる)、両側INOは多発性硬化症で示唆的。PPRF/VI核障害=患側への水平注視麻痺(病巣側を見られない)で、VI核病変は同側顔面神経麻痺を伴いうる。PPRF(またはVI核)＋同側MLF障害=one-and-a-half症候群。

MLF lesion = internuclear ophthalmoplegia (INO): impaired adduction of the ipsilateral eye with dissociated abducting nystagmus (convergence preserved); bilateral INO suggests multiple sclerosis. PPRF/VI nucleus lesion = ipsilateral horizontal gaze palsy (cannot look toward the lesion), and a VI nucleus lesion may add ipsilateral facial palsy. PPRF (or VI nucleus) plus ipsilateral MLF = one-and-a-half syndrome.

臨床症候・疾患 / Clinical correlations

内側縦束(MLF)障害で核間性眼筋麻痺(INO: 患側の内転障害＋対側外転眼の眼振)。橋傍正中網様体(PPRF)または外転神経核の障害で病巣側への水平注視麻痺。これに同側 MLF 障害を伴うと one-and-a-half 症候群。若年・両側性 INO は多発性硬化症、高齢・片側は脳幹梗塞を示唆。

Medial longitudinal fasciculus (MLF) lesion causes internuclear ophthalmoplegia (INO: impaired adduction on the affected side + abducting nystagmus of the other eye). A PPRF or abducens-nucleus lesion causes ipsilateral horizontal gaze palsy; adding an ipsilateral MLF lesion produces one-and-a-half syndrome. Young/bilateral INO suggests multiple sclerosis; older/unilateral suggests brainstem infarct.

Clinical pearl — MLF 障害=核間性眼筋麻痺(INO)。若年両側なら多発性硬化症を疑う。

MLF lesion = internuclear ophthalmoplegia (INO); young + bilateral suggests multiple sclerosis.

出典 / References

• Leigh RJ, Zee DS. The Neurology of Eye Movements, 5th ed.
• Standring S. Gray's Anatomy, 42nd ed.

同じ系統の回路

• 脳神経核・皮質延髄路