motor evoked potentials measure the conduction of impulses through
the motor portion of the spinal cord. The cortex of the
brain is stimulated electrically, through the scalp, and then
nerve action potentials are recorded from motor nerves in the
extremities or from mechanical activity in the muscles.
Like somatosensory evoked potentials (ssep's), they may be helpful
in protecting the function of the spinal cord when the
neurosurgeon is operating in or around the cord.