Medial longitudinal fasciculus
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|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|
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.
The medial longitudinal fasciculus carries information about the direction that the eyes should move.
It connects 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.
The descending MLF mainly arises from the Superior-medial Vestibular nucleus (VN) and is thought to be involved in the maintenance of gaze reflex (stimulated by input form Semicircular canal). This is achieved by inputs to the VN from:
- the Vestibulocochlear (8th cranial) nerve about head movements,
- gait adjustments from the flocculus of the cerebellum,
- 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.
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.
- Medial+longitudinal+fasciculus at eMedicine Dictionary
- Atlas image: n2a4p4 at the University of Michigan Health System - "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View"