The medial longitudinal fasciculus (MLF) is an area of

crossed over ''Crossed Over'' is a 2002 Canadian television film directed by Bobby Roth, and starring Diane Keaton as Beverly Lowry and Jennifer Jason Leigh as Karla Faye Tucker. It is based on Lowry's memoir ''Crossed Over: A Murder, A Memoir''. Cast *Dian ...

tracts, on each side of the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...

. These bundles of

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...

s are situated near the midline of the

. 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 In neuroanatomy, the superior colliculus () is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum, or optic lobe. The adjective form ''tectal'' is commonly ...

, the

vestibular nuclei The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica they are grouped in both the pons and the medulla in the brainstem. Structure Path The fibers of the vestibular n ...

, and the

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

. It contains the

interstitial nucleus of Cajal An interstitial space or interstice is a space between structures or objects. In particular, interstitial may refer to: Biology * Interstitial cell tumor * Interstitial cell, any cell that lies between other cells * Interstitial collagenase, ...

, responsible for oculomotor control, head posture, and vertical eye movement. The medial longitudinal fasciculus is the main central connection for the oculomotor nerve,

trochlear nerve The trochlear nerve (), ( lit. ''pulley-like'' nerve) also known as the fourth cranial nerve, cranial nerve IV, or CN IV, is a cranial nerve that innervates just one muscle: the superior oblique muscle of the eye, which operates through the pu ...

, and

abducens nerve 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 extraocul ...

. It carries information about the direction that the

eyes Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conve ...

should move.

Lesions A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

of the medial longitudinal fasciculus can cause

nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. Infants can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision. Due to the invol ...

and

diplopia Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often v ...

, which may be associated with

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...

, a

neoplasm A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

, or a

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

Structure

The medial longitudinal fasciculus is an area of

tracts, on each side of the

. It is medial, and close to the

periaqueductal gray The periaqueductal gray (PAG, also known as the central gray) is a brain region that plays a critical role in autonomic function, motivated behavior and behavioural responses to threatening stimuli. PAG is also the primary control center for d ...

matter around the

cerebral aqueduct The cerebral aqueduct (aqueductus mesencephali, mesencephalic duct, sylvian aqueduct or aqueduct of Sylvius) is a conduit for cerebrospinal fluid (CSF) that connects the third ventricle to the fourth ventricle of the ventricular system of the brai ...

. It is found between the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

(caudally) and the

pretectum In neuroanatomy, the pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in mediati ...

(cranially). It connects with the

, the

, and the

. It contains the

. The medial longitudinal fasciculus also contains the rostral interstitial nucleus (riMLF), which is the vertical gaze center. Descending fibers arise from the

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 The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica they are grouped in both the pons and the medulla in the brainstem. Structure Path The fibers of the vestibular nerv ...

and terminate in the

oculomotor nucleus The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From t ...

(of the oculomotor nerve, CN III), the

trochlear nucleus The nucleus of the trochlear nerve () is located in the midbrain, at an intercollicular level between the superior colliculus and inferior colliculus. It is a motor nucleus, and so is located near the midline, embedded within the medial longitudina ...

(of the

, CN IV), and the

abducens nucleus 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, medial to the sulcus limitans. The abd ...

(of the

, CN VI). These three nuclei lie alongside the medial longitudinal fasciculus.

Function

The medial longitudinal fasciculus carries information about the direction that the eyes should move. It connects the nuclei of the oculomotor nerve (CN III), the

(CN IV), and the

(CN VI). It integrates movements directed by the gaze centers (frontal eye field) and information about head movement (from the

vestibulocochlear nerve The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the bra ...

, CN VIII). It is an integral component of saccadic eye movements, as well as

vestibulo–ocular reflex 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 ...

, and the

optokinetic reflex The optokinetic response is a combination of a slow-phase and fast-phase eye movements. It is seen when an individual tracks (pursuit movement) a moving object with their eyes, which then moves out of the field of vision, a point at which their ...

. It also carries the descending

tectospinal tract In humans, the tectospinal tract (or colliculospinal tract) is a nerve tract that coordinates head and eye movements. This tract is part of the extrapyramidal system and connects the midbrain tectum, and cervical regions of the spinal cord. It ...

and

medial vestibulospinal tract The medial vestibulospinal tract is one of the descending spinal tracts of the ventromedial funiculus of the spinal cord. It is found only in the cervical spine and above. The medial part of the vestibulospinal tract is the smaller part, and is pr ...

s into the cervical

, and innervates some muscles of the

neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

and upper limbs.

Vestibulo-ocular reflex

The medial longitudinal fasciculus is involved in the generation of the

. This is achieved by inputs to the

from: # the

(CN VIII). This is related to head movements. # the flocculus of the

. This is related to gait adjustments. #

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...

and

proprioceptors Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...

and

foot The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...

and

ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular join ...

muscle spindle Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be ...

, via the

fastigial nucleus The fastigial nucleus is located in the cerebellum. It is one of the four deep cerebellar nuclei (the others being the nucleus dentatus, nucleus emboliformis and nucleus globosus), and is grey matter embedded in the white matter of the cerebell ...

. This is related to position.

Clinical significance

A lesion of the medial longitudinal fasciculus produces slowed or absent adduction of the ipsilateral eye upon contralateral gaze. This is usually associated with involuntary jerky

eye movement Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms (e.g. primates, rodents, flies, birds, fish, cats, crabs, octopus) to fixate, inspect and track visual objects of interest ...

s (

) of the abducting eye, a syndrome called

internuclear ophthalmoplegia Internuclear ophthalmoplegia (INO) is a disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction. When an attempt is made to gaze contralaterally (relative to the affected eye), the affected eye adducts minimally ...

. Because

causes

demyelination A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency i ...

of the axons of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

, it can cause internuclear ophthalmoplegia when medial longitudinal fasciculus axons get demyelinated.Multiple Sclerosis Encyclopaedia
/ref> This presents as nystagmus and

. Other

demyelinating disease A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency i ...

s, as well as certain

neoplasms A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

and

strokes A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop funct ...

, can also cause the same symptoms.

History

In 1846,

neurologist Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal c ...

Benedict Stilling Benedikt Stilling (11 February 1810 – 28 January 1879) was a German anatomist and surgeon who was a native of Kirchhain. He was the father of German ophthalmologist Jakob Stilling (1842–1915). In 1832 he received his doctorate from the Univ ...

first referred to the medial longitudinal fasciculus as the ''acusticus''. This was followed by

Theodor Meynert Theodor Hermann Meynert (15 June 1833 – 31 May 1892) was a German-Austrian psychiatrist, neuropathologist and anatomist born in Dresden. Meynert believed that disturbances in brain development could be a predisposition for psychiatric illness a ...

in 1872 calling it ''posterior''. In 1891,

Heinrich Schutz Heinrich may refer to: People * Heinrich (given name), a given name (including a list of people with the name) * Heinrich (surname), a surname (including a list of people with the name) *Hetty (given name), a given name (including a list of peo ...

chose the name ''dorsal'' to describe the longitudinal bundle. This name stuck despite other authors attempting further renaming ( Ramon y Cajal's ''periependymal'' in 1904,

Theodor Ziehen Georg Theodor Ziehen (12 November 1862 – 29 December 1950) was a German neurologist and psychiatrist born in Frankfurt am Main. He was the son of noted author, Eduard Ziehen (1819–1884). Education and career As a gymnasium student, Ziehen s ...

's ''nubecula dorsalis'' in 1913). Finally, Wilhelm His Sr. changed the name to ''medial'' to comply with Basle nomenclature.

Additional images

File:Gray680.png, Decussation of pyramids.

References

External links

* - "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View" * https://web.archive.org/web/20091021004541/http://isc.temple.edu/neuroanatomy/lab/atlas/papc/ {{DEFAULTSORT:Medial Longitudinal Fasciculus Brainstem Central nervous system pathways

Structure

Function

Vestibulo-ocular reflex

Clinical significance

History

Additional images

See also

References

External links