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| 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 oftegmentum. 8.Oculomotor nerve, with 8’, its nucleus of origin. a.Lemniscus (in blue) with a’ themedial lemniscus and a" thelateral lemniscus. b.Medial longitudinal fasciculus. c.Raphe. d.Temporopontine fibers. e. Portion ofmedial lemniscus, which runs to thelentiform nucleus andinsula. f.Cerebrospinal fibers. g.Frontopontine fibers. | |
| Details | |
| Identifiers | |
| Latin | fasciculus longitudinalis medialis |
| NeuroNames | 1588,784 |
| NeuroLex ID | nlx_144065 |
| TA98 | A14.1.04.113 A14.1.05.304 A14.1.06.209 |
| TA2 | 5867 |
| FMA | 83846 |
| Anatomical terms of neuroanatomy | |
Themedial longitudinal fasciculus (MLF) is a prominent bundle of nerve fibres which pass within the ventral/anterior portion ofperiaqueductal gray of themesencephalon (midbrain).[1] It contains theinterstitial nucleus of Cajal, responsible for oculomotor control, head posture, and vertical eye movement.[2]
The MLF interconnects interneurons of eachabducens nucleus with motor neurons of the contralateraloculomotor nucleus; thus, the MLF mediates coordination of horizontal (side to side) eye movements, ensuring the two eyes move in unison (thus also enablingsaccadic eye movements). The MLF also contains fibers projecting from thevestibular nuclei to theoculomotor andtrochlear nuclei as well as theinterstitial nucleus of Cajal; these connections ensure that eye movements are coordinated with head movements (as sensed by thevestibular system).[1]
The medial longitudinal fasciculus is the main central connection for theoculomotor nerve,trochlear nerve, andabducens nerve. It carries information about the direction that theeyes should move.Lesions of the medial longitudinal fasciculus can causenystagmus anddiplopia, which may be associated withmultiple sclerosis, aneoplasm, or astroke.
The MLF is the main intersegmental tract of the brainstem. It extends across the dorsal tegmentum of all three parts of the brainstem, as well as reaching caudally into the upper cervical spinal cord levels.[3]: 451
Descending fibers arise from thesuperior colliculus in the rostral midbrain (for visualreflexes), the accessory oculomotor nuclei in the rostral midbrain for visual tracking, and the pontine reticular formation, which facilitates extensor muscle tone. Ascending tracts arise from thevestibular nucleus and terminate in theoculomotor nucleus (of theoculomotor nerve, CN III), thetrochlear nucleus (of thetrochlear nerve, CN IV), and theabducens nucleus (of theabducens nerve, CN VI).[4]
It contains theinterstitial nucleus of Cajal,[2] and therostral interstitial nucleus (riMLF)[1] (thevertical gaze center).
The paramedian pontine reticular formation (PMPRF) is involved in coordinating horizontal conjugate eye movements and saccades. To do so, besides projecting to the ipsilateral abducens nucleus, the PMPRF projects fibers through the MLF to the contralateraloculomotor nucleus (specifically, those of its motor neurons that innervate themedial rectus muscle).
The interstitial nucleus of Cajal receives some ascending afferents from the vestibular nuclei via the MLF; the nucleus in turn projects descending efferents via the MLF back to the (superior and medial) vestibular nuclei, as well as to all levels of the spinal cord.[3]: 458.e1
As part of theascending MLF, the vestibular nuclei also project to the nuclei of all cranial nerves that control eye movements (i.e. oculomotor, abducens, and trochlear nuclei) to coordinate head-eye movements via thevestibulo-ocular reflex.[5]: 287-288
The three perihypoglossal nuclei project efferents to the threecranial nerve nuclei controllingextrinsic eye muscles through the MLF.[6]
The vestibulocerebellum receivesvestibulocerebellar fibers from thevestibular nuclei, then projects back to thevestibular nuclei to influencemedial vestibulospinal tract (MVST). The MVST then projects bilaterally to cervical and upper thoracic levels of the spinal cord to control head/neck movements in order to coordinate head-eye movements. In the cervical spinal cord, it descends as a component of thedescending MLF.[5]: 287-288, 403
The tectospinal tract originates in thesuperior colliculus andtectum of themesencephalon (midbrain). It projects to the cervical and upper thoracic spinal cord to mediate reflex turning of the head and trunk in the direction of startling sensations. In themedulla oblongata, it descends within the MLF.
In the midbrain, the MLF is situated just ventral to the oculomotor and trochlear nuclei.[3]
In the pons, the MLF is situated just ventral/anterior to the abducens nucleus.[3]
A lesion of the medial longitudinal fasciculus produces slowed or absent adduction of the ipsilateral eye upon contralateral gaze.[7] This is usually associated with involuntary jerkyeye movements (nystagmus) of the abducting eye, a syndrome calledinternuclear ophthalmoplegia.[7] Becausemultiple sclerosis causesdemyelination of the axons of thecentral nervous system, it can cause internuclear ophthalmoplegia when medial longitudinal fasciculus axons get demyelinated.[8] This presents as nystagmus anddiplopia.[7] Otherdemyelinating diseases, as well as certainneoplasms andstrokes, can also cause the same symptoms.[7]
In 1846,neurologistBenedict Stilling first referred to the medial longitudinal fasciculus as theacusticus.[9] This was followed byTheodor Meynert in 1872 calling itposterior.[9] In 1891,Heinrich Schutz chose the namedorsal to describe the longitudinal bundle.[9] This name stuck despite other authors attempting further renaming (Ramon y Cajal'speriependymal in 1904,Theodor Ziehen'snubecula dorsalis in 1913).[9] Finally,Wilhelm His Sr. changed the name tomedial to comply withBasle nomenclature.[9]
