Medial longitudinal fasciculus

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Medial longitudinal fasciculus
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Transverse section of mid-brain at level of inferior colliculi. (Medial longitudinal fasciculus labeled at center right.)
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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 oforigin. a. Lemniscus (in blue) with a’ the medial lemniscus and a" the lateral lemniscus. b. Medial longitudinal fasciculus. c. Raphe. d. Temporopontine fibers. e. Portion of medial lemniscus, which runs to the lentiform nucleus and insula. 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

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). [1] It contains the interstitial nucleus of Cajal, responsible for oculomotor control, head posture, and vertical eye movement. [2]

Contents

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). [1]

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.

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. [3] : 451 

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). [4]

Structure

It contains the interstitial nucleus of Cajal, [2] and the rostral interstitial nucleus (riMLF) [1] (the vertical gaze center).

Pathways

Horizontal conjugate gaze

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 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. [3] : 458.e1 

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. [5] : 287-288 

Perihypoglossal nuclei

The three perihypoglossal nuclei project efferents to the three cranial nerve nuclei controlling extrinsic eye muscles through the MLF. [6]

Medial vestibulospinal tract

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. [5] : 287-288, 403 

Tectospinal tract

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.

Relations

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]

Clinical significance

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 jerky eye movements (nystagmus) of the abducting eye, a syndrome called internuclear ophthalmoplegia. [7] 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. [8] This presents as nystagmus and diplopia. [7] Other demyelinating diseases, as well as certain neoplasms and strokes, can also cause the same symptoms. [7]

History

In 1846, neurologist Benedict Stilling first referred to the medial longitudinal fasciculus as the acusticus. [9] This was followed by Theodor Meynert in 1872 calling it posterior. [9] In 1891, Heinrich Schutz chose the name dorsal to describe the longitudinal bundle. [9] This name stuck despite other authors attempting further renaming (Ramon y Cajal's periependymal in 1904, Theodor Ziehen's nubecula dorsalis in 1913). [9] Finally, Wilhelm His Sr. changed the name to medial to comply with Basle nomenclature. [9]

Additional images

See also

Related Research Articles

<span class="mw-page-title-main">Sense of balance</span> Physiological sense regarding posture

The sense of balance or equilibrioception is the perception of balance and spatial orientation. It helps prevent humans and nonhuman animals from falling over when standing or moving. Equilibrioception is the result of a number of sensory systems working together; the eyes, the inner ears, and the body's sense of where it is in space (proprioception) ideally need to be intact.

<span class="mw-page-title-main">Abducens nerve</span> Cranial nerve VI, for eye movements

The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocular muscles responsible for outward gaze. It is a somatic efferent nerve.

<span class="mw-page-title-main">Brainstem</span> Posterior part of the brain, adjoining and structurally continuous

The brainstem is the stalk-like part of the brain that connects the forebrain with the spinal cord. In the human brain, the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch.

<span class="mw-page-title-main">Vestibulo–ocular reflex</span> Reflex where rotation of the head causes eye movement to stabilize vision

The vestibulo-ocular reflex (VOR) is a reflex that acts to stabilize gaze during head movement, with eye movement due to activation of the vestibular system, it is also known as the Cervico-ocular reflex. The reflex acts to stabilize images on the retinas of the eye during head movement. Gaze is held steadily on a location by producing eye movements in the direction opposite that of head movement. For example, when the head moves to the right, the eyes move to the left, meaning the image a person sees stays the same even though the head has turned. Since slight head movement is present all the time, VOR is necessary for stabilizing vision: people with an impaired reflex find it difficult to read using print, because the eyes do not stabilise during small head tremors, and also because damage to reflex can cause nystagmus.

<span class="mw-page-title-main">Abducens nucleus</span>

The abducens nucleus is the originating nucleus from which the abducens nerve (VI) emerges—a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the caudal portion of the pons near the midline, medial to the sulcus limitans.

<span class="mw-page-title-main">Parinaud's syndrome</span> Inability to move the eyes up and down

Parinaud's syndrome is a constellation of neurological signs indicating injury to the dorsal midbrain. More specifically, compression of the vertical gaze center at the rostral interstitial nucleus of medial longitudinal fasciculus (riMLF).

<span class="mw-page-title-main">Paramedian pontine reticular formation</span>

The paramedian pontine reticular formation (PPRF) is a subset of neurons of the oral and caudal pontine reticular nuclei mediating horizontal gaze. It is situated in the pons adjacent to the abducens nucleus. It projects to the ipsilateral abducens nucleus, and contralateral oculomotor nucleus to mediate conjugate horizontal eye movements and saccades.

<span class="mw-page-title-main">Vestibulospinal tract</span> Neural tract in the central nervous system

The vestibulospinal tract is a neural tract in the central nervous system. Specifically, it is a component of the extrapyramidal system and is classified as a component of the medial pathway. Like other descending motor pathways, the vestibulospinal fibers of the tract relay information from nuclei to motor neurons. The vestibular nuclei receive information through the vestibulocochlear nerve about changes in the orientation of the head. The nuclei relay motor commands through the vestibulospinal tract. The function of these motor commands is to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head.

<span class="mw-page-title-main">Trochlear nucleus</span> Motor nucleus of cranial nerve IV

The nucleus of the trochlear nerve is a motor nucleus in the medial midbrain giving rise to the trochlear nerve.

<span class="mw-page-title-main">Vestibular nuclei</span>

The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem.

<span class="mw-page-title-main">Lateral vestibular nucleus</span>

The lateral vestibular nucleus is the continuation upward and lateralward of the principal nucleus, and in it terminate many of the ascending branches of the vestibular nerve.

<span class="mw-page-title-main">Medial vestibular nucleus</span>

The medial vestibular nucleus is one of the vestibular nuclei. It is located in the medulla oblongata.

<span class="mw-page-title-main">Rostral interstitial nucleus of medial longitudinal fasciculus</span>

The rostral interstitial nucleus of medial longitudinal fasciculus (riMLF) is a collection of neurons in the mesencephalon (midbrain) responsible for mediating vertical conjugate eye movements and vertical saccades. It mostly projects efferents to the ipsilateral oculomotor and trochlear nuclei.

The term gaze is frequently used in physiology to describe coordinated motion of the eyes and neck. The lateral gaze is controlled by the paramedian pontine reticular formation (PPRF). The vertical gaze is controlled by the rostral interstitial nucleus of medial longitudinal fasciculus and the interstitial nucleus of Cajal.

<span class="mw-page-title-main">Nucleus prepositus</span>

The nucleus prepositus or nucleus prepositus hypoglossi is one of the largest of the three perihypoglossal nuclei. It is situated in the caudal pons and rostral medulla oblongata. It contributes to several aspects of gaze control including the horizontal gaze holding system.

Conjugate eye movement refers to motor coordination of the eyes that allows for bilateral fixation on a single object. A conjugate eye movement is a movement of both eyes in the same direction to maintain binocular gaze. This is in contrast to vergence eye movement, where binocular gaze is maintained by moving eyes in opposite directions, such as going “cross eyed” to view an object moving towards the face. Conjugate eye movements can be in any direction, and can accompany both saccadic eye movements and smooth pursuit eye movements.

Perihypoglossal nuclei are three prominent groups of neurons in the caudal medulla oblongata near the hypoglossal nucleus: the nucleus prepositus hypoglossi, intercalated nucleus, and sublingual nucleus. They are involved in controlling eye movements: they send their principal projections to the three cranial nerve nuclei controlling extrinsic eye muscles via the medial longitudinal fasciculus.

<span class="mw-page-title-main">Corticomesencephalic tract</span>

In neuroanatomy, corticomesencephalic tract is a descending nerve tract that originates in the frontal eye field and terminate in the midbrain. Its fibers mediate conjugate eye movement.

The interstitial nucleus of Cajal is a collection of neurons in the mesencephalon (midbrain) which are involved in integrating eye position-velocity information in order to coordinate head-eye movements - especially those related to vertical and torsional conjugate eye movements (gaze). It also mediates vertical gaze holding.

The nucleus of Darkschewitsch is an accessory oculomotor nucleus situated in the ventrolateral portion of the periaqueductal gray of the mesencephalon (midbrain) near its junction with the diencephalon. It is involved in mediating vertical eye movements. It projects to the trochlear nucleus, receives afferents from the visual cortex, and forms a reciprocal (looping) connection with the cerebellum by way of the inferior olive.

References

  1. 1 2 3 Waitzman, David M.; Oliver, Douglas L. (2002). "Midbrain". Encyclopedia of the Human Brain. Academic Press. pp. 43–68. doi:10.1016/B0-12-227210-2/00208-9. ISBN   978-0-12-227210-3.
  2. 1 2 Yu, Megan; Wang, Shu-Min (2022), "Neuroanatomy, Interstitial Nucleus of Cajal", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   31613454 , retrieved 2022-03-12
  3. 1 2 3 4 Standring, Susan (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice (42th ed.). New York: Elsevier. ISBN   978-0-7020-7707-4. OCLC   1201341621.
  4. ↑ Walter, B. L.; Shaikh, A. G. (2014). "Midbrain". Encyclopedia of the Neurological Sciences - Reference Module in Neuroscience and Biobehavioral Psychology (2nd ed.). Academic Press. pp. 28–33. doi:10.1016/B978-0-12-385157-4.01161-1. ISBN   978-0-12-385158-1.
  5. 1 2 Patestas, Maria A.; Gartner, Leslie P. (2016). A Textbook of Neuroanatomy (2nd ed.). Hoboken, New Jersey: Wiley-Blackwell. ISBN   978-1-118-67746-9.
  6. ↑ Kiernan, John A.; Rajakumar, Nagalingam (2013). Barr's The Human Nervous System: An Anatomical Viewpoint (10th ed.). Philadelphia: Wolters Kluwer Lippincott Williams & Wilkins. p. 156. ISBN   978-1-4511-7327-7.
  7. 1 2 3 4 Strominger, Mitchell B. (2008). "13 - Strabismus: Miscellaneous". Pediatric Ophthalmology and Strabismus. Mosby. pp. 195–200, 202–210. doi:10.1016/B978-0-323-05168-2.50018-2. ISBN   978-0-323-05168-2.
  8. ↑ Multiple Sclerosis Encyclopaedia
  9. 1 2 3 4 5 F, Schiller (1984). "When Is Posterior Not Dorsal but Medial?". Neurology. 34 (4): 511–514. doi:10.1212/wnl.34.4.511. PMID   6366612. S2CID   26881440 . Retrieved 2020-06-04.
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