What is the role of subcortical projections of the pyramidal pathway in motor evoked potentials (MEPs)?

Updated: Aug 20, 2019
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Selim R Benbadis, MD  more...
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Pyramidal fibers converge in the corona radiata, toward the posterior arm of the internal capsule. In the pons, they divide into multiple longitudinal pathways, which merge in the medulla oblongata to form the pyramidal tract after branching out efferences to motor nuclei of cranial nerves.

At the junction between the medulla oblongata and the spinal cord, 75-90% of the fibers cross through the midline to constitute the crossed (ie, indirect) pyramidal pathway. The remaining fibers make up the uncrossed (ie, direct) pyramidal pathway. A large part of direct pyramidal tract fibers actually cross the midline at the spinal cord level (ie, through the white anterior commissura), making the projections bilateral.

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