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Posterior column-medial lemniscus pathway

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Posterior column-medial lemniscus pathway
Spinal nerve
The formation of the spinal nerve from the dorsal and ventral roots.
Latin {{{Latin}}}
[[List of subjects in Gray's Anatomy:{{{GraySubject}}}#Gray.27s_page_.23|Gray's]] subject #{{{GraySubject}}}
System Somatosensory system
MeSH {{{MeshNumber}}}
Gray759
Originating in peripheral sensory receptors, the posterior column-medial lemniscus pathway transmits fine touch and conscious proprioceptive information to the brain.

The posterior column-medial lemniscus pathway is the sensory pathway responsible for transmitting fine touch, vibration and conscious proprioceptive information from the body to the cerebral cortex.[1]

The name comes from the two structures that the sensation travels up: the posterior (or dorsal) columns of the spinal cord, and the medial lemniscus in the brainstem. Because the posterior columns are also called dorsal columns, the pathway is often called the dorsal column-medial lemniscus system, or DCML for short. (Also called posterior column-medial lemniscus or PCML pathway).

JourneyEdit

Discriminative sensation is well developed in the fingers of humans, and allows us to feel fine textures and determine what an unknown object in our hands is without looking at it (stereognosis).

First neuronEdit

This fine sensation is detected by Meissner's corpuscles that lie in the dermis of the skin close to the epidermis. When these structures are stimulated by slight pressure, an action potential is started. Alternatively, proprioceptive muscle spindles and other skin surface touch receptors such as merkel cells, Ruffini endings, Pacinian corpuscles, and hair follicle receptors may involve the first neuron in this pathway.

The action potential travels up an axon (the cell body of the neuron will be in a dorsal root ganglion). (The neurons are classified as pseudo-unipolar, so they are regarded as having just one long process, which includes both a peripheral branch dendrite and central branch axon.) So the sensation travels from the skin, along the axon, past the neuronal cell body, and into the dorsal column of the spinal cord.

The axons continue inside the spinal cord, running up the posterior (dorsal) column. Axons from the lower body are most medial (closer to the midline), and run in the gracile tract of the spinal column. Sensory axons from the upper body enter the spinal cord later, so are more lateral and travel up the cuneate tract.

At the level of the closed medulla oblongata, these axons synapse with neurons in the gracile nucleus and cuneate nucleus.

Second neuronEdit

The secondary neurons (that start in the nuclei) cross over to the other side of the medulla (as internal arcuate fibres) to form the medial lemniscus. This crossing over is commonly referred to as the sensory decussation.

At the medulla, the medial lemniscus is orientated perpendicular to the way the fibres travelled in the posterior columns. For example, in the columns, lower limb is medial, upper limb is more lateral. At the medial leminiscus, axons from the leg are more ventral, arm fibres more dorsal. Fibres from the trigeminal nerve (supplying the head) come in dorsal to the arm fibres, and travel up the lemniscus too.

The medial lemniscus rotates 90 degrees at the pons. The secondary axons from neurons giving sensation to the head, stay at around the same place, while the leg axons move outwards.

The axons travel up the rest of the brainstem, and synapse at the thalamus (at the ventral posterolateral nucleus for sensation from the neck, trunk, and extremities, and at the ventral posteromedial nucleus for sensation from the head).

Third neuronEdit

Neurons starting in the thalamus travel up the posterior limb of the internal capsule, and again head and leg swap relative positions. The axons synapse in the primary sensory cortex, with lower body sensation most medial (e.g., the paracentral lobule) and upper body more lateral.

See alsoEdit

ReferencesEdit

  1. Physiology at MCG 8/8ch5/s8ch5_22

External linksEdit

Spinal cord

epidural space, dura mater, subdural space, arachnoid mater, subarachnoid space, pia mater, denticulate ligaments, conus medullaris, cauda equina, filum terminale, cervical enlargement, lumbar enlargement, anterior median fissure, dorsal root, dorsal root ganglion, dorsal ramus, ventral root, ventral ramus, sympathetic trunk, gray ramus communicans, white ramus communicans

grey matter: central canal, substantia gelatinosa of Rolando, reticular formation, substantia gelatinosa centralis, interneuron, anterior horn, lateral horn, posterior horn (column of Clarke, dorsal spinocerebellar tract)

white matter: anterior funiculus: descending (anterior corticospinal tract, vestibulospinal fasciculus, tectospinal tract), ascending (anterior spinothalamic tract, anterior proper fasciculus)

lateral funiculus: descending (lateral corticospinal tract, rubrospinal tract, olivospinal tract), ascending dorsal spinocerebellar tract, ventral spinocerebellar tract, spinothalamic tract, lateral spinothalamic tract, anterior spinothalamic tract, spinotectal tract, posterolateral tract, lateral proper fasciculus, medial longitudinal fasciculus

posterior funiculus: fasciculus gracilis, fasciculus cuneatus, posterior proper fasciculus


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