The Medial Lemniscus-Dorsal Column pathway is an ascending spinal tract, carrying sensory information to the brain. It is typically depicted as a chain of three neurons: first-, second-, and third-order neurons.
This pathway mediates:
- Conscious proprioception (most clinically relevant)
- Sensation of tactile discrimination
- Vibration sense
- Form recognition
First order neurons
The first-order neurons in the pathway are located in the dorsal root ganglia at all spinal levels, giving rise to the fasciculus gracilis tract in the lower extremity and the fasciculus cuneatus tract in the upper extremity. The axons comprising these funiculi ascend ipsilaterally to the medulla, where they synapse with the second-order neurons.
Second order neurons
The second-order neurons are located in the cadual medulla, and their cell bodies form the gracile and cuneate nuclei. Their axons, referred to as internal arcuate fibers, decussate to form the medial lemniscus, which ascends the contralateral brainstem to project to the ventral posterolateral (VPL) nucleus of the thalamus.
Third order neurons
The third-order VPL neurons send axons through the posterior limb of the internal capsule to the somatosensory cortex (areas 3, 1, 2)
Spinal cord lesions affecting the dorsal column (e.g., vitamin B12 neuropathy, tabes dorsalis) result in ipsilateral sensory deficits below the lesion, because the pathway does not decussate until it is at the level of the medulla.
I love this. I think I probably love you too, for succintly describing and doing a lovely little doodle of the DCML. Big love.
My neuro biology professor confused me today… This has saved me… Thank you for making it simple!
Hey guys, I am glad to hear that my sketch has been useful in your studies! I will be making more guest doodles on Sketchy Medicine in the future, on many different topics (but I do love neuro quite a bit). Medicine rocks!
Thank you for the simplistic summary!!!! :)
Awesome! Thank you!
I learned about the nervous system 2 years ago this made relearning everything so much easier and simpler! Thank you !
Hey this is great! Really helps a lot. But why the arrows go down instead of go up in ascending pathway?
Sorry for the confusion, they are actually supposed to represent synapses :)
Why does it have ipsilateral effects if the fibers decussate?
It depends where the fibers decussate and how distal the lesion is. Ipsilateral spinal fibers in this tract stay ipsilateral until the medulla, where they cross over and continue the rest of the way to the cortex contralaterally.
A lesion above that decussation would definitely cause a contralateral lesion. (L medial lemniscus lesion -> R proprioception impairment)
A lesion in the spine would affect the ipsilateral side because the fibers would not have crossed over yet. (L dorsal column lesion -> L proprioception loss)
Hope that helps! (It’s been a few years since I last reviewed this so I hope I got it right!)
Thank you so much for your simple pathway.