Posterior column-medial lemniscus pathway
624265
223435525
2008-07-04T01:54:03Z
Gold Dragon
91439
/* Second neuron */ refer specifically to the sensory decussation
{{Infobox Anatomy |
Name = {{PAGENAME}} |
Image = Spinal nerve.svg |
Caption = The formation of the spinal nerve from the dorsal and ventral roots. |
Image2 = Gray759.png |
Caption2 = Originating in peripheral [[sensory receptor]]s, the posterior column-medial lemniscus pathway transmits fine touch and conscious [[proprioception|proprioceptive]] information to the brain. |
System = [[Somatosensory system]]|
Precursor = [[Neural tube]] and [[neural crest|crest]] |
}}
The '''posterior column-medial lemniscus pathway''' is the [[sense|sensory]] pathway responsible for transmitting ''[[touch|fine touch]]'', ''[[vibration]]'' and ''[[proprioception|conscious proprioceptive]]'' information from the body to the [[cerebral cortex]].<ref>{{GeorgiaPhysiology|8/8ch5/s8ch5_22}}</ref>
The name comes from the two structures that the sensation travels up: the [[Posterior columns|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).
==Journey==
Discriminative sensation is well developed in the fingers of [[human]]s, and allows us to feel fine textures and determine what an unknown object in our hands is without looking at it ([[stereognosis]]).
===First neuron===
This fine sensation is detected by [[Meissner's corpuscle]]s that lie in the [[dermis]] of the [[skin]] close to the [[epidermis (skin)|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 neuron===
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 (anatomy)|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 neuron===
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.
==References==
<references/>
==External links==
* http://www.ualberta.ca/~neuro/OnlineIntro/SysSensorySomatic.htm#Paths
{{Spinal cord}}
{{Neural tracts}}
[[Category: Perception]]
[[Category:Central nervous system pathways]]
[[fr:Voie lemniscale]]
[[pl:Droga sznurów grzbietowych]]