The medial longitudinal fasciculus (MLF) is a paired bundle of fibres running near the midline of the brainstem, just beneath the floor of the fourth ventricle and cerebral aqueduct. It links the nuclei that move the eyes with each other and with the vestibular nuclei, so that the two eyes move together and stay steady when the head moves.
| Location | Paramedian dorsal brainstem from the upper midbrain to the cervical spinal cord, close to the oculomotor, trochlear, abducens and hypoglossal nuclei |
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| Connections |
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| Blood Supply | Paramedian branches of the basilar artery; Paramedian midbrain perforators |
Coordinates conjugate eye movements and links eye movements to head and neck movement and balance.
A lesion of the MLF causes internuclear ophthalmoplegia: the eye on the side of the lesion fails to turn inward on sideways gaze, while the other eye shows nystagmus. In young adults, especially when bilateral, the usual cause is multiple sclerosis; in older people it is often a small stroke. Combined with an abducens nucleus lesion it causes the one-and-a-half syndrome.
Impaired adduction of one eye with nystagmus of the abducting eye from an MLF lesion, commonly due to multiple sclerosis or stroke.
A pontine lesion of the abducens nucleus and MLF leaving only abduction of the opposite eye as horizontal movement.
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