Medial lemniscus

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Medial lemniscus
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The sensory tract. (Medial lemniscus labeled at top right.)
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Coronal section through mid-brain. ("e" is Portion of medial lemniscus, which runs to the lentiform nucleus and insula. "a’" is also the medial lemniscus.)
Details
Identifiers
Latin lemniscus medialis
NeuroLex ID birnlex_887
TA98 A14.1.04.111
A14.1.08.672
A14.1.06.207
TA2 5861
FMA 83675
Anatomical terms of neuroanatomy

In neuroanatomy, the medial lemniscus, also known as Reil's band or Reil's ribbon (for German anatomist Johann Christian Reil), is a large ascending bundle of heavily myelinated axons that decussate (cross) in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally.

Contents

The medial lemniscus is part of the dorsal column–medial lemniscus pathway, which ascends from the skin to the thalamus, [1] which is important for somatosensation from the skin and joints, therefore, lesion of the medial lemnisci causes an impairment of vibratory and touch-pressure sense.

Etymology

Lemniscus means "ribbon", so named because the medial lemniscus "spirals" or "turns" as it ascends.

Path

After neurons carrying proprioceptive or fine touch information synapse at the gracile and cuneate nuclei, axons from secondary neurons decussate at the level of the medulla and travel up the brainstem as the medial lemniscus on the contralateral (opposite) side. It is part of the posterior column-medial lemniscus pathway, which transmits touch, vibration sense, as well as the pathway for proprioception.

The medial lemniscus carries axons from most of the body and synapses in the ventral posterolateral nucleus of the thalamus, at the level of the mamillary bodies. Sensory axons transmitting information from the head and neck via the trigeminal nerve synapse at the ventral posteromedial nucleus of the thalamus.

Location through the brainstem

[2]

See also

Additional images

Related Research Articles

Medulla oblongata Structure of the brain stem

The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involuntary) functions, ranging from vomiting to sneezing. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers, and therefore deals with the autonomic functions of breathing, heart rate and blood pressure as well as the sleep wake cycle.

Pronator quadratus is a square-shaped muscle on the distal forearm that acts to pronate the hand.

Brainstem Posterior part of the brain, adjoining and structurally continuous

The brainstem 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 continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

Trigeminal nerve Cranial nerve responsible for the faces senses and motor functions

In neuroanatomy, the trigeminal nerve, also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name ("trigeminal", from Latin tri- 'three', and -geminus 'twin') derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.

Internal capsule White matter structure situated in the inferomedial part of each cerebral hemisphere of the brain

The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus. The internal capsule contains both ascending and descending axons, going to and coming from the cerebral cortex. It also separates the caudate nucleus and the putamen in the dorsal striatum, a brain region involved in motor and reward pathways.

Neural pathway

A neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable a signal to be sent from one region of the nervous system to another. Neurons are connected by a single axon, or by a bundle of axons known as a nerve tract, or fasciculus. Shorter neural pathways are found within grey matter in the brain, whereas longer projections, made up of myelinated axons, constitute white matter.

Spinothalamic tract Sensory pathway from the skin to the thalamus

The spinothalamic tract is a part of the anterolateral system or the ventrolateral system, a sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.

Dorsal column–medial lemniscus pathway Sensory spinal pathway

The dorsal column–medial lemniscus pathway (DCML) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints. It transmits information from the body to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain. The pathway receives information from sensory receptors throughout the body, and carries this in nerve tracts in the white matter of the dorsal column of the spinal cord to the medulla, where it is continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex. The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.

Lateral lemniscus

The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain. Three distinct, primarily inhibitory, cellular groups are located interspersed within these fibers, and are thus named the nuclei of the lateral lemniscus.

Spinocerebellar tract

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.

Facial motor nucleus

The facial motor nucleus is a collection of neurons in the brainstem that belong to the facial nerve. These lower motor neurons innervate the muscles of facial expression and the stapedius.

Cochlear nucleus Two cranial nerve nuclei of the human brainstem

The cochlear nuclear (CN) complex comprises two cranial nerve nuclei in the human brainstem, the ventral cochlear nucleus (VCN) and the dorsal cochlear nucleus (DCN). The ventral cochlear nucleus is unlayered whereas the dorsal cochlear nucleus is layered. Auditory nerve fibers, fibers that travel through the auditory nerve carry information from the inner ear, the cochlea, on the same side of the head, to the nerve root in the ventral cochlear nucleus. At the nerve root the fibers branch to innervate the ventral cochlear nucleus and the deep layer of the dorsal cochlear nucleus. All acoustic information thus enters the brain through the cochlear nuclei, where the processing of acoustic information begins. The outputs from the cochlear nuclei are received in higher regions of the auditory brainstem.

Cerebellar peduncle Structure connecting the cerebellum to the brainstem

Cerebellar peduncles connect the cerebellum to the brain stem. There are six cerebellar peduncles in total, three on each side:

Dorsal column nuclei Nuclei in the dorsal column of the brainstem

In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the bottom of the medulla oblongata. Both nuclei contain second-order neurons of the dorsal column–medial lemniscus pathway, which carries fine touch and proprioceptive information from the body to the brain. Fibres reach the thalamus.

Sensory decussation Crossing of axons between the gracile and cuneate nuclei of the brain

In neuroanatomy, the sensory decussation or decussation of the lemnisci is a decussation of axons from the gracile nucleus and cuneate nucleus, which are responsible for fine touch, vibration, proprioception and two-point discrimination of the body. The fibres of this decussation are called the internal arcuate fibres and are found at the superior aspect of the closed medulla superior to the motor decussation. It is part of the second neuron in the posterior column–medial lemniscus pathway.

The ventral trigeminal tract, ventral trigeminothalamic tract, anterior trigeminal tract, or anterior trigeminothalamic tract, is a tract composed of second order neuronal axons. These fibers carry sensory information about discriminative and crude touch, conscious proprioception, pain, and temperature from the head, face, and oral cavity. The ventral trigeminal tract connects the two major components of the brainstem trigeminal complex – the principal, or main sensory nucleus and the spinal trigeminal nucleus, to the ventral posteromedial nucleus of the thalamus.

The trigeminal lemniscus, also called the trigeminothalamic tract, is composed of the ventral trigeminal tract, and the dorsal trigeminal tract – nerve tracts that convey tactile, pain, and temperature impulses from the skin of the face, the mucous membranes of the nasal and oral cavities, and the eye, as well as proprioceptive information from the facial and masticatory muscles.

The dorsal trigeminal tract, dorsal trigeminothalamic tract, or posterior trigeminothalamic tract, is composed of second-order neuronal axons. These fibers carry sensory information about discriminative touch and conscious proprioception in the oral cavity from the principal nucleus of the trigeminal nerve to the ventral posteromedial (VPM) nucleus of the thalamus.

Spinal cord Long, tubular central nervous system structure in the vertebral column

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 spinal cord, which contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone, passing through the foramen magnum and then enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) long in adult men and around 43 cm (17 in) long in adult women. The diameter of the spinal cord ranges from 13 mm in the cervical and lumbar regions to 6.4 mm in the thoracic area.

References

  1. Kamali A, Kramer LA, Butler IJ, Hasan KM. Diffusion tensor tractography of the somatosensory system in the human brainstem: initial findings using high isotropic spatial resolution at 3.0 T. Eur Radiol. 2009 19:1480-8. doi : 10.1007/s00330-009-1305-x.
  2. Purves et al, Neuroscience 5th edition, Sinauer Massachusetts, p. 198