What is the role of the pyramidal tract 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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Fibers of the corticospinal tract and corticobulbar tract originate from the sensorimotor cortex around the central sulcus. The human pyramidal tract contains more than 1 million fibers. Most fibers are myelinated and have a small diameter (1-4mm); only a small portion (3-5%) are large-diameter fibers (10-22mm) that originate in Betz cells from area 4.

In humans, only 5% of the fibers of the corticospinal tract originate from Betz cells in area 4. The concept of pyramidal pathways with fibers originating only from Betz cells in the primary motor cortex has been invalidated. Indeed, a large portion of the corticospinal neurons have nonmotor functions, especially those originating in sensory or associative areas.

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