View source for Medial longitudinal fasciculus

{{Short description|Nerve tracts in the brainstem}}
{{More citations needed|date=April 2008}}
{{Infobox brain
| Name            = Medial longitudinal fasciculus
| Latin           = fasciculus longitudinalis medialis
| Image           = File:Gray711.png
| Caption         = Transverse section of mid-brain at level of inferior colliculi. (Medial longitudinal fasciculus labeled at center right.)
| Image2          = File:Gray710.png
| Caption2        = Axial section through mid-brain.  <br>1. [[Corpora quadrigemina]]. <br>2. [[Cerebral aqueduct]]. <br>3. [[Central gray stratum]]. <br>4. [[Interpeduncular space]]. <br>5. [[Sulcus lateralis]]. <br>6. [[Substantia nigra]]. <br>7. [[Red nucleus]] of [[tegmentum]]. <br>8. [[Oculomotor nerve]], with 8’, its nucleus of origin. a. [[Lemniscus (anatomy)|Lemniscus]] (in blue) with a’ the [[medial lemniscus]] and a" the [[lateral lemniscus]]. b. '''Medial longitudinal fasciculus'''. c. [[Raphe nuclei|Raphe]]. d. [[Temporopontine fibers]]. e. Portion of [[medial lemniscus]], which runs to the [[lentiform nucleus]] and [[Insular cortex|insula]]. f. [[Cerebrospinal fibers]]. g. [[Frontopontine fibers]].
| IsPartOf        =
| Components      =
| Artery          =
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}}

<!-- Structure -->
The '''medial longitudinal fasciculus''' ('''MLF''') is a prominent bundle of nerve fibres which pass within the ventral/anterior portion of [[periaqueductal gray]] of the [[mesencephalon]] (midbrain).<ref name="Waitzman-2002">{{Cite book |last1=Waitzman |first1=David M. |title=Encyclopedia of the Human Brain |last2=Oliver |first2=Douglas L. |publisher=[[Academic Press]] |year=2002 |isbn=978-0-12-227210-3 |pages=43–68 |language=en |chapter=Midbrain |doi=10.1016/B0-12-227210-2/00208-9 |chapter-url=https://www.sciencedirect.com/science/article/pii/B0122272102002089}}</ref> It contains the [[interstitial nucleus of Cajal]], responsible for oculomotor control, head posture, and vertical eye movement.<ref name="Yu-2022">{{Citation |last1=Yu |first1=Megan |title=Neuroanatomy, Interstitial Nucleus of Cajal |date=2022 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK547674/ |access-date=2022-03-12 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=31613454 |last2=Wang |first2=Shu-Min}}</ref>

The MLF interconnects interneurons of each [[abducens nucleus]] with motor neurons of the contralateral [[oculomotor nucleus]]; thus, the MLF mediates coordination of horizontal (side to side) eye movements, ensuring the two eyes move in unison (thus also enabling [[Saccade|saccadic eye movements]]). The MLF also contains fibers projecting from the [[vestibular nuclei]] to the [[Oculomotor nucleus|oculomotor]] and [[Trochlear nucleus|trochlear nuclei]] as well as the [[interstitial nucleus of Cajal]]; these connections ensure that eye movements are coordinated with head movements (as sensed by the [[vestibular system]]).<ref name="Waitzman-2002" />

<!-- Function and Clinical Significance -->
The medial longitudinal fasciculus is the main central connection for the [[oculomotor nerve]], [[trochlear nerve]], and [[abducens nerve]]. It carries information about the direction that the [[Eye|eyes]] should move. [[Lesion|Lesions]] of the medial longitudinal fasciculus can cause [[nystagmus]] and [[diplopia]], which may be associated with [[multiple sclerosis]], a [[neoplasm]], or a [[stroke]].

== Anatomy ==
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.<ref name="Standring-2020">{{Cite book |last=Standring |first=Susan |title=Gray's Anatomy: The Anatomical Basis of Clinical Practice |publisher=[[Elsevier]] |year=2020 |isbn=978-0-7020-7707-4 |edition=42th |location=New York |pages= |oclc=1201341621}}</ref>{{Rp|page=451}}

Descending fibers arise from the [[superior colliculus]] in the rostral midbrain (for visual [[Reflex|reflexes]]), 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 the [[vestibular nucleus]] and terminate in the [[oculomotor nucleus]] (of the [[oculomotor nerve]], CN III), the [[trochlear nucleus]] (of the [[trochlear nerve]], CN IV), and the [[abducens nucleus]] (of the [[abducens nerve]], CN VI).<ref>{{Cite book |last1=Walter |first1=B. L. |title=Encyclopedia of the Neurological Sciences - Reference Module in Neuroscience and Biobehavioral Psychology |last2=Shaikh |first2=A. G. |publisher=[[Academic Press]] |year=2014 |isbn=978-0-12-385158-1 |edition=2nd |pages=28–33 |language=en |chapter=Midbrain |doi=10.1016/B978-0-12-385157-4.01161-1 |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780123851574011611}}</ref>

=== Structure ===
It contains the [[interstitial nucleus of Cajal]],<ref name="Yu-2022" /> and the [[Rostral interstitial nucleus of medial longitudinal fasciculus|rostral interstitial nucleus]] (riMLF)<ref name="Waitzman-2002" /> (the [[vertical gaze center]]). 

=== Pathways ===

==== Horizontal conjugate gaze ====
{{Main articles|Paramedian pontine reticular formation}}
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 contralateral [[oculomotor nucleus]] (specifically, those of its motor neurons that innervate the [[medial rectus muscle]]).

==== Interstitial nucleus of Cajal ====
{{Main articles|Interstitial nucleus of Cajal}}

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.<ref name="Standring-2020" />{{Rp|page=458.e1}}

==== Vestibulo-ocular reflex ====
{{Main articles|Vestibulo-ocular reflex}}

As part of the ''ascending'' 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 the [[vestibulo-ocular reflex]].<ref name="Patestas-2016">{{Cite book |last1=Patestas |first1=Maria A. |title=A Textbook of Neuroanatomy |last2=Gartner |first2=Leslie P. |publisher=Wiley-Blackwell |year=2016 |isbn=978-1-118-67746-9 |edition=2nd |location=Hoboken, New Jersey}}</ref>{{Rp|page=287-288}}

==== Perihypoglossal nuclei ====
{{Main article|Perihypoglossal nuclei}}
The three perihypoglossal nuclei project efferents to the three [[Cranial nerve nucleus|cranial nerve nuclei]] controlling [[extrinsic eye muscles]] through the MLF.<ref>{{Cite book |last1=Kiernan |first1=John A. |title=Barr's The Human Nervous System: An Anatomical Viewpoint |last2=Rajakumar |first2=Nagalingam |publisher=Wolters Kluwer Lippincott Williams & Wilkins |year=2013 |isbn=978-1-4511-7327-7 |edition=10th |location=Philadelphia |pages=156}}</ref>

==== Medial vestibulospinal tract ====
{{Main articles|Medial vestibulospinal tract}}

The vestibulocerebellum receives [[Vestibulocerebellar tract|vestibulocerebellar fibers]] from the [[vestibular nuclei]], then projects back to the [[vestibular nuclei]] to influence [[Medial vestibulospinal tract|medial 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 the ''descending'' MLF.<ref name="Patestas-2016" />{{Rp|page=287-288, 403}}

==== Tectospinal tract ====
{{Main articles|Tectospinal tract}}

The tectospinal tract originates in the [[superior colliculus]] and [[tectum]] of the [[Mesencephalic|mesencephalon (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 the [[medulla oblongata]], it descends within the MLF.

=== Relations ===
In the midbrain, the MLF is situated just ventral to the oculomotor and trochlear nuclei.<ref name="Standring-2020" />

In the pons, the MLF is situated just ventral/anterior to the abducens nucleus.<ref name="Standring-2020" />

== Clinical significance ==
A lesion of the medial longitudinal fasciculus produces slowed or absent adduction of the ipsilateral eye upon contralateral gaze.<ref name="Strominger-2008">{{Cite book|last=Strominger|first=Mitchell B.|chapter-url=https://www.sciencedirect.com/science/article/pii/B9780323051682500182|title=Pediatric Ophthalmology and Strabismus|publisher=[[Mosby (publisher)|Mosby]]|year=2008|isbn=978-0-323-05168-2|pages=195-200, 202-210|language=en|chapter=13 - Strabismus: Miscellaneous|doi=10.1016/B978-0-323-05168-2.50018-2}}</ref> This is usually associated with involuntary jerky [[eye movement]]s ([[nystagmus]]) of the abducting eye, a syndrome called [[internuclear ophthalmoplegia]].<ref name="Strominger-2008" /> Because [[multiple sclerosis]] causes [[demyelinating disease|demyelination]] of the axons of the [[central nervous system]], it can cause internuclear ophthalmoplegia when medial longitudinal fasciculus axons get demyelinated.<ref>[http://www.mult-sclerosis.org/mediallongitudinalfasciculus.html Multiple Sclerosis Encyclopaedia]</ref> This presents as nystagmus and [[diplopia]].<ref name="Strominger-2008" /> Other [[demyelinating disease]]s, as well as certain [[Neoplasm|neoplasms]] and [[Stroke|strokes]], can also cause the same symptoms.<ref name="Strominger-2008" />

== History ==
In 1846, [[neurology|neurologist]] [[Benedict Stilling]] first referred to the medial longitudinal fasciculus as the ''acusticus''.<ref name="F-1984">{{Cite journal|last=F|first=Schiller|date=1984|title=When Is Posterior Not Dorsal but Medial?|journal=Neurology|volume=34|issue=4|pages=511–514|doi=10.1212/wnl.34.4.511|language=en|pmid=6366612|s2cid=26881440 }}</ref> This was followed by [[Theodor Meynert]] in 1872 calling it ''posterior''.<ref name="F-1984" /> In 1891, [[Heinrich Schutz]] chose the name ''dorsal'' to describe the longitudinal bundle.<ref name="F-1984" /> This name stuck despite other authors attempting further renaming ([[Ramon y Cajal]]'s ''periependymal'' in 1904, [[Theodor Ziehen]]'s ''nubecula dorsalis'' in 1913).<ref name="F-1984" /> Finally, [[Wilhelm His Sr.]] changed the name to ''medial'' to comply with [[Basle nomenclature]].<ref name="F-1984" />

== Additional images ==
<gallery>
 File:Gray680.png|Decussation of pyramids.
</gallery>

== See also ==
* [[Listing's law]]

== References ==
<references/>

== External links ==
* {{UMichAtlas|n2a4p4}} - "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View"
* https://web.archive.org/web/20091021004541/http://isc.temple.edu/neuroanatomy/lab/atlas/papc/
{{Medulla}}
{{Pons}}
{{Mesencephalon}}
{{Visual system}}
{{Authority control}}

{{DEFAULTSORT:Medial Longitudinal Fasciculus}}
[[Category:Brainstem]]
[[Category:Central nervous system pathways]]