Medial longitudinal fasciculus

Brain: Medial longitudinal fasciculus
Transverse section of mid-brain at level of inferior colliculi. (Medial longitudinal fasciculus labeled at center right.)
Axial section through mid-brain. 1. Corpora quadrigemina. 2. Cerebral aqueduct. 3. Central gray stratum. 4. Interpeduncular space. 5. Sulcus lateralis. 6. Substantia nigra. 7. Red nucleus of tegmentum. 8. Oculomotor nerve, with 8’, its nucleus of origin. a. Lemniscus (in blue) with a’ the medial lemniscus and a" the lateral lemniscus. b. Medial longitudinal fasciculus. c. Raphé. d. Temporopontine fibers. e. Portion of medial lemniscus, which runs to the lentiform nucleus and insula. f. Cerebrospinal fibers. g. Frontopontine fibers.
Latin	fasciculus longitudinalis medialis
Gray's	subject #188 803
NeuroNames	ancil-743

The medial longitudinal fasciculus (MLF) is a pair of crossed fiber tracts (group of axons), one on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are composed of both ascending and descending fibers that arise from a number of sources and terminate in different areas.

Function

The MLF carries information about the direction that the eyes should move.

It yokes the cranial nerve nuclei III (Oculomotor nerve), IV (Trochlear nerve) and VI (Abducens nerve) together, and integrates movements directed by the gaze centers (frontal eye field) and information about head movement (from cranial nerve VIII, Vestibulocochlear nerve). It is an integral component of saccadic eye movements as well as vestibulo-ocular and optokinetic reflexes.

It also carries the descending tectospinal tract and medial vestibulospinal tracts into the cervical spinal cord, and innervates some muscles of the neck and upper limbs.

Inputs

The descending MLF mainly arises from the medial Vestibular nucleus (VN) and is thought to be involved in the maintenance of gaze. This is achieved by inputs to the VN from

1. the Vestibulocochlear (8th cranial) nerve about head movements,
2. gain adjustments from the flocculus of the cerebellum,
3. head and neck propioceptors and foot and ankle muscle spindle, via the fastigial nucleus.

Descending fibers can also arise from the superior colliculus in the rostral midbrain for visual reflexes, the accessory occulomotor nuclei in the rostral midbrain for visual tracking, and the pontine reticular formation, which facilitates extensor muscle tone. Ascending tracts arise from the Vestibular nucleus (VN) and terminate in the III, IV and VI nuclei, which are important for visual tracking.

Pathology

Lesions of the MLF produce internuclear ophthalmoplegia and can be a presenting symptom of multiple sclerosis,^[1] where it presents as nystagmus and occasionally diplopia.^[2] These lesions cause damage to the ipsilateral (same side) eye, but nystagmus on the contralateral (opposite side) eye.

History

In 1846 neurologist Benedict Stilling first referred to what is now known as the MLF as the acusticus, followed by Theodor Meynert in 1872 calling it posterior. But in 1891, Heinrich Schutz chose the name dorsal to describe the longitudinal bundle, "for brevity's sake". This name stuck despite other authors attempting further renaming (Ramon y Cajal's periependymal in 1904, Theodor Ziehen's nubecula dorsalis in 1913). But finally, it was Wilhelm His, Sr. who changed the name to medial for the sake of the Basle nomenclature to end the confusion.

Additional images

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  Decussation of pyramids.

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  Transverse section of medulla oblongata below the middle of the olive.

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  Horizontal section through the lower part of the pons. The medial longitudinal fasciculus is labeled #6.

References

1. ^ Multiple Sclerosis Encyclopaedia
2. ^ Internuclear Ophthalmoplegia

External links

• Medial+longitudinal+fasciculus at eMedicine Dictionary
• Atlas of anatomy at UMich n2a4p4 - "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View"
• http://isc.temple.edu/neuroanatomy/lab/atlas/papc/