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Medial longitudinal fasciculus | |
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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 an area of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem. They are made up of both ascending and descending fibers that arise from a number of sources and terminate in different areas, including the superior colliculus, the vestibular nuclei, and the cerebellum. It contains the interstitial nucleus of Cajal, responsible for oculomotor control, head posture, and vertical eye movement. [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.
The medial longitudinal fasciculus is an area of crossed over tracts, on each side of the brainstem. [2] It is medial, and close to the periaqueductal gray matter around the cerebral aqueduct. [3] It is found between the spinal cord (caudally) and the pretectum (cranially). [4] It connects with the superior colliculus, the vestibular nuclei, and the cerebellum. [4] It contains the interstitial nucleus of Cajal. [1] The medial longitudinal fasciculus also contains the rostral interstitial nucleus (riMLF), [3] which is the vertical gaze center.
Descending fibers arise from the superior colliculus in the rostral midbrain (for visual reflexes), [2] 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). [2] These three nuclei lie alongside the medial longitudinal fasciculus. [4]
The medial longitudinal fasciculus carries information about the direction that the eyes should move. [2] It connects the nuclei of the oculomotor nerve (CN III), the trochlear nerve (CN IV), and the abducens nerve (CN VI). [2] It integrates movements directed by the gaze centers (frontal eye field) and information about head movement (from the vestibulocochlear nerve, CN VIII). It is an integral component of saccadic eye movements, [2] as well as vestibulo–ocular reflex, [3] and the optokinetic reflex.
It also carries the descending tectospinal tract and medial vestibulospinal tracts into the cervical spinal cord, and innervates some muscles of the neck and upper limbs.
The medial longitudinal fasciculus is involved in the generation of the vestibulo–ocular reflex. [3] This is achieved by inputs to the vestibular nucleus from:
A lesion of the medial longitudinal fasciculus produces slowed or absent adduction of the ipsilateral eye upon contralateral gaze. [5] This is usually associated with involuntary jerky eye movements (nystagmus) of the abducting eye, a syndrome called internuclear ophthalmoplegia. [5] 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. [6] This presents as nystagmus and diplopia. [5] Other demyelinating diseases, as well as certain neoplasms and strokes, can also cause the same symptoms. [5]
In 1846, neurologist Benedict Stilling first referred to the medial longitudinal fasciculus as the acusticus. [7] This was followed by Theodor Meynert in 1872 calling it posterior. [7] In 1891, Heinrich Schutz chose the name dorsal to describe the longitudinal bundle. [7] This name stuck despite other authors attempting further renaming (Ramon y Cajal's periependymal in 1904, Theodor Ziehen's nubecula dorsalis in 1913). [7] Finally, Wilhelm His Sr. changed the name to medial to comply with Basle nomenclature. [7]
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.
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.
Articles related to anatomy include:
The pons is part of the brainstem that in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.
The brainstem is the stalk-like part of the brain that interconnects the cerebrum and diencephalon 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.
The midbrain or mesencephalon is the rostral-most portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum.
The vestibulo-ocular reflex (VOR) is a reflex acting to stabilize gaze during head movement, with eye movement due to activation of the vestibular system. 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.
The pontine tegmentum, or dorsal pons, is located within the brainstem, and is one of two parts of the pons, the other being the ventral pons or basilar part of the pons. The pontine tegmentum can be defined in contrast to the basilar pons: basilar pons contains the corticospinal tract running craniocaudally and can be considered the rostral extension of the ventral medulla oblongata; however, basilar pons is distinguished from ventral medulla oblongata in that it contains additional transverse pontine fibres that continue laterally to become the middle cerebellar peduncle. The pontine tegmentum is all the material dorsal from the basilar pons to the fourth ventricle. Along with the dorsal surface of the medulla, it forms part of the rhomboid fossa – the floor of the fourth ventricle.
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.
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).
The flocculus is a small lobe of the cerebellum at the posterior border of the middle cerebellar peduncle anterior to the biventer lobule. Like other parts of the cerebellum, the flocculus is involved in motor control. It is an essential part of the vestibulo-ocular reflex, and aids in the learning of basic motor skills in the brain.
A cranial nerve nucleus is a collection of neurons in the brain stem that is associated with one or more of the cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei except that of the trochlear nerve supply nerves of the same side of the body.
The nucleus of the trochlear nerve is a motor nucleus in the medial midbrain giving rise to the trochlear nerve.
The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem.
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.
The medial vestibular nucleus is one of the vestibular nuclei. It is located in the medulla oblongata.
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.
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.
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.