neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defin ...

, the medial lemniscus, also known as Reil's band or Reil's ribbon (for German anatomist

Johann Christian Reil Johann Christian Reil (20 February 1759 – 22 November 1813) was a German physician, physiologist, anatomist, and psychiatrist. He coined the term psychiatry – ''Psychiatrie'' in German – in 1808. Medical conditions and anatomical featur ...

), is a large ascending bundle of heavily myelinated

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 that

decussate Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named aft ...

(cross) in 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 ...

, specifically in the

medulla oblongata 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 (involun ...

. The medial lemniscus is formed by the crossings of the

internal arcuate fibers In neuroanatomy, the internal arcuate fibers or internal arcuate tract are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata. These second-order neurons begin in the gracile and cunea ...

. The internal arcuate fibers are composed of axons of nucleus gracilis and

nucleus cuneatus 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 nu ...

. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally. The medial lemniscus is part of the

dorsal column–medial lemniscus pathway The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial lemniscus pathway, PCML) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discriminatio ...

, which ascends from the skin to the

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...

, 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 In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

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 Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to its head ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability The posterior probability is a type of conditional probability that r ...

, 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 The ventral posterolateral nucleus (VPL) is a nucleus of the thalamus. Together with the ventral posteromedial nucleus (VPM), ventral posterior inferior nucleus (VPI) and ventromedial posterior nucleus (VMpo), it constitutes the ventral posterior ...

of the

, at the level of the

mamillary bodies The mammillary bodies are a pair of small round bodies, located on the undersurface of the brain that, as part of the diencephalon, form part of the limbic system. They are located at the ends of the anterior arches of the fornix. They consis ...

. Sensory axons transmitting information from the head and neck via the

trigeminal nerve In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' 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 chewin ...

synapse at the

ventral posteromedial nucleus The ventral posteromedial nucleus (VPM) is a nucleus of the thalamus. Inputs and outputs The VPM contains synapses between second and third order neurons from the anterior (ventral) trigeminothalamic tract and posterior (dorsal) trigeminothalami ...

of the

Location through the brainstem

* The cuneate and gracile nuclei reside at the ''closed (lower)

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...

'', so the lemniscus is not formed at this level. Fibres from these nuclei will pass to the contralateral side of the brainstem, as the

internal arcuate fibres In neuroanatomy, the internal arcuate fibers or internal arcuate tract are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata. These second-order neurons begin in the gracile and cu ...

. * At the ''open medulla'' (further up the brainstem), the medial lemniscus contains axons from the

(which supplies the head region), as well as the arms and legs. It sits very close to the midline, at the same orientation of the midline, with head fibres more dorsal (closer to the back), towards the

fourth ventricle The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ve ...

. * By ''mid-

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Va ...

'', the medial lemniscus has rotated. Fibres from the head are medial, fibres from the leg are lateral. * The orientation in the ''

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

'' is similar to that in the pons. Purves et al, Neuroscience 5th edition, Sinauer Massachusetts, p. 198

Additional images

File:Gray685.png, Deep dissection of brain-stem. Lateral view. File:Gray690.png, Deep dissection of brain-stem. Ventral view. File:Gray701.png, Coronal section of the pons, at its upper part. File:Gray711.png, Transverse section of mid-brain at level of inferior colliculi. File:Gray713.png, Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red. File:Lower pons horizontal KB.svg, Horizontal section through the lower part of the pons. The medial lemniscus is labeled #17. File:Medial Lemniscus.jpg, Tractography showing medial lemniscus

References

External links