The medial longitudinal fasciculus (MLF) is a pair of crossed fiber tracts (group of axon

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s), one on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are composed of both ascending and descending fibers that arise from a number of sources and terminate in different areas.

Function

The Medial Longitudinal Fasciculus carries information about the direction that the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

s should move.

It yokes the cranial nerve nuclei III

Oculomotor nerve

The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the Levator palpebrae superiors muscle. The optic nerve is...

 (Oculomotor nerve), IV

Trochlear nerve

The trochlear nerve is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye....

 (Trochlear nerve) and VI (Abducens nerve) together, and integrates movements directed by the gaze centers (frontal eye field) and information about head movement (from cranial nerve VIII, Vestibulocochlear nerve). It is an integral component of saccadic eye movements as well as vestibulo-ocular

Vestibulo-ocular reflex

The vestibulo-ocular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the...

 and optokinetic reflex

Optokinetic reflex

The optokinetic reflex allows the eye to follow objects in motion when the head remains stationary . The reflex develops at about 6 months of age.-See also:...

es.

It also carries the descending tectospinal tract

Tectospinal tract

In humans, the tectospinal tract is a nerve pathway which coordinates head and eye movements. It is part of the indirect extrapyramidal tract...

 and medial vestibulospinal tract

Vestibulospinal tract

The vestibulospinal tract is a component of the extrapyramidal system and also can be classified as a component of the medial pathway. The vestibulospinal fibers relay information from nuclei to motor neurons, like other descending motor pathways. Specifically, the vestibular nuclei receive...

s into the cervical spinal cord

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

, and innervates some muscles of the neck

Neck

The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...

 and upper limbs.

Inputs

The descending MLF mainly arises from the medial Vestibular nucleus (VN) and is thought to be involved in the maintenance of gaze

Gaze

Gaze is a psychoanalytical term brought into popular usage by Jacques Lacan to describe the anxious state that comes with the awareness that one can be viewed. The psychological effect, Lacan argues, is that the subject loses some sense of autonomy upon realizing that he or she is a visible object...

. This is achieved by inputs to the VN from

1. the Vestibulocochlear (8th cranial) nerve about head movements,
2. gain adjustments from the flocculus of the cerebellum
   Cerebellum
   The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
   
   ,
3. head
   Head
   In anatomy, the head of an animal is the rostral part that usually comprises the brain, eyes, ears, nose and mouth . Some very simple animals may not have a head, but many bilaterally symmetric forms do....
   
    and neck
   Neck
   The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
   
    propioceptors and foot
   Foot
   The foot 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 up of one or more segments or bones, generally including claws...
   
    and ankle
   Ankle
   The ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
   
    muscle spindle
   Muscle spindle
   Muscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons. This information can be processed by the brain to determine the position of body parts...
   
   , via the fastigial nucleus
   Fastigial nucleus
   The fastigial nucleus or nucleus fastigii refers specifically to the concentration of gray matter nearest to the middle line at the anterior end of the superior vermis, and immediately over the roof of the fourth ventricle, from which it is separated by a thin layer of white matter...
   
   .

Descending fibers can also arise from the superior colliculus

Superior colliculus

The optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a...

 in the rostral midbrain for visual reflexes, the accessory occulomotor 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 (VN) and terminate in the III

Oculomotor nerve

The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the Levator palpebrae superiors muscle. The optic nerve is...

, IV

Trochlear nerve

The trochlear nerve is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye....

 and VI nuclei, which are important for visual tracking.

Pathology

Lesions of the MLF produce internuclear ophthalmoplegia

Internuclear ophthalmoplegia

Internuclear ophthalmoplegia is a disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction. When an attempt is made to gaze contralaterally , the affected eye adducts minimally, if at all. The contralateral eye abducts, however with nystagmus...

 and can be a presenting symptom of multiple sclerosis

Multiple sclerosis

Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...

, where it presents as nystagmus and o;p89

History

In 1846 neurologist

Neurology

Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...

 Benedict Stilling

Benedict Stilling

Benedikt Stilling was a German anatomist and surgeon who was a native of Kirchhain. In 1832 he received his doctorate from the University of Marburg...

 first referred to what is now known as the MLF as the acusticus, followed by Theodor Meynert

Theodor Meynert

Theodor Hermann Meynert was a German-Austrian neuropathologist and anatomist who was born in Dresden.In 1861 he earned his medical doctorate, and in 1875 became director of the psychiatric clinic associated with the University of Vienna. One of his better known students in Vienna was Sigmund...

 in 1872 calling it posterior. But in 1891, Heinrich Schutz

Heinrich Schütz

Heinrich Schütz was a German composer and organist, generally regarded as the most important German composer before Johann Sebastian Bach and often considered to be one of the most important composers of the 17th century along with Claudio Monteverdi...

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

Theodor Ziehen

Georg Theodor Ziehen was a German neurologist and psychiatrist born in Frankfurt am Main. He was the son of noted author, Eduard Ziehen ....

's nubecula dorsalis in 1913). But finally, it was Wilhelm His, Sr.

Wilhelm His, Sr.

Wilhelm His, Sr. was a Swiss anatomist and professor who invented the microtome...

 who changed the name to medial for the sake of the Basle nomenclature to end the confusion.

External links

- "Brainstem, Cranial Nerve Nuclei, Sagittal Section, Medial View"

• http://isc.temple.edu/neuroanatomy/lab/atlas/papc/