Template:Short description Template:More citations needed Template:Infobox brain
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">Template:Cite book</ref> It contains the interstitial nucleus of Cajal, responsible for oculomotor control, head posture, and vertical eye movement.<ref name="Yu-2022">Template:Citation</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 saccadic eye movements). The MLF also contains fibers projecting from the vestibular nuclei to the oculomotor and 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" />
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 eyes should move. Lesions of the medial longitudinal fasciculus can cause nystagmus and diplopia, which may be associated with multiple sclerosis, a neoplasm, or a stroke.
AnatomyEdit
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">Template:Cite book</ref>Template:Rp
Descending fibers arise from the superior colliculus in the rostral midbrain (for visual 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>Template:Cite book</ref>
StructureEdit
It contains the interstitial nucleus of Cajal,<ref name="Yu-2022" /> and the rostral interstitial nucleus (riMLF)<ref name="Waitzman-2002" /> (the vertical gaze center).
PathwaysEdit
Horizontal conjugate gazeEdit
Template:Main articles The paramedian pontine reticular formation (PMPRF) is involved in coordinating horizontal conjugate eye movements and saccades. To do so, besides projecting to the ibsilateral 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 CajalEdit
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" />Template:Rp
Vestibulo-ocular reflexEdit
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">Template:Cite book</ref>Template:Rp
Perihypoglossal nucleiEdit
Template:Main article The three perihypoglossal nuclei project efferents to the three cranial nerve nuclei controlling extrinsic eye muscles through the MLF.<ref>Template:Cite book</ref>
Medial vestibulospinal tractEdit
The vestibulocerebellum receives vestibulocerebellar fibers from the vestibular nuclei, then projects back to the vestibular nuclei to influence 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" />Template:Rp
Tectospinal tractEdit
The tectospinal tract originates in the superior colliculus and tectum of the 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.
RelationsEdit
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 significanceEdit
A lesion of the medial longitudinal fasciculus produces slowed or absent adduction of the ipsilateral eye upon contralateral gaze.<ref name="Strominger-2008">Template:Cite book</ref> This is usually associated with involuntary jerky eye movements (nystagmus) of the abducting eye, a syndrome called internuclear ophthalmoplegia.<ref name="Strominger-2008" /> Because multiple sclerosis causes demyelination of the axons of the central nervous system, it can cause internuclear ophthalmoplegia when medial longitudinal fasciculus axons get demyelinated.<ref>Multiple Sclerosis Encyclopaedia</ref> This presents as nystagmus and diplopia.<ref name="Strominger-2008" /> Other demyelinating diseases, as well as certain neoplasms and strokes, can also cause the same symptoms.<ref name="Strominger-2008" />
HistoryEdit
In 1846, neurologist Benedict Stilling first referred to the medial longitudinal fasciculus as the acusticus.<ref name="F-1984">Template:Cite journal</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 imagesEdit
- Gray680.png
Decussation of pyramids.
See alsoEdit
ReferencesEdit
<references/>
External linksEdit
- Template:UMichAtlas - "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View"
- https://web.archive.org/web/20091021004541/http://isc.temple.edu/neuroanatomy/lab/atlas/papc/
Template:Medulla Template:Pons Template:Mesencephalon Template:Visual system Template:Authority control