I was told by a physician today that UMNs stop at about the T7 level, and below that all motor neurons are LMN, so if you had any spinal pathology below that level you would only see LMN signs. I don't remember that, and am having a hard time finding it in my limited book collection. I thought UMNs went down to all levels, and synapsed with LMNs in the anterior horn (at any level before the spinal cord terminates). Can anyone shed some light on this for me?
UMN/LMN Question
- Thread starter hoddemic
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I think that there was a mistake somewhere in this communication. You are correct that upper motor neurons ultimately synapse with lower motor neurons in the anterior horn, where the lower motor neuron cell bodies are. What may have been meant was that the spinal cord ends in the bony spine above the level that the nerves are exiting. This is most dramatic in the lower thoracic and lumbar regions, where the end of the cord sits near the L1 or L2 vertebrae in adults, with only a collection of the nerve roots traveling through the lumbar spinal canal below that point. Lack of this knowledge results in some poor imaging choices by practitioners who attempt to image the lumbar bony spine when looking for evidence of an UMN lesion, when the pathology must lie in the thoracic region or higher.
