Pathway and typical responses of the motor evoked potential

Motor evoked potentials (MEPs) are produced by stimulation of the motor cortex (arrow). The electrical activity descends following the corticospinal tract to the anterior horn of the spinal cord. After synapsing, the response then further descends to the peripheral nerve, traverses the neuromuscular junction, and produces a muscle response. The MEP can be measured in the epidural space as D- and I-waves or as a compound muscle action potential (CMAP).