and 12 ma at myotome locations ml 1 ml 2 ml 3 mr 1 mr 2 and mr 3 respectively as can be seen twice the intensity of current was required to produce a neuro muscular response at mr 2 as was required to produce a neuro muscular response at mr 3 since u201c 24 u201d ma is twice as big as u201c 12 u201d ma thus the nerve pathway to mr 3 is more u201c sensitive u201d than to mr 2 since mr 3 is able to exhibit a neuro muscular response at u00bd of the current intensity required to exhibit a neuro muscular response at mr 2 consequently during nerve detection when electrode 21 or 23 positioned on the distal end of tool probe 20 or 22 is positioned adjacent the nerve root affiliated with mr 3 twice the current stimulation intensity was required to produce an emg response in contrast when electrode 21 or 23 on the distal end of tool probe 20 or 22 was positioned adjacent to the nerve root affiliated with mr 2 the same level of stimulation that produced a response at mr 3 would not produce a response at mr 2 in accordance with preferred aspects of the present invention the sensitivities of the various spinal nerve pathways to their associated myotomes are incorporated into the nerve detection function of the invention by incorporating the various neuro muscular response onset values as follows a decision is made that either of electrodes 21 or 23.