TetraSens electrode array has two proximal stimulating electrodes, one recording electrode and one reference electrode. The application is easy and quick. TetraSens electrode array is for single-patient use in order to avoid cross contamination. The electrodes can be applied on either hand, with the stimulation electrodes over the ulnar nerve at the wrist and the evoked response recorded from any of the hand muscles; typically, either the muscle at the base of the little finger (abductor digiti minimi muscle), or, more commonly, from the muscle at the base of the thumb, adductor pollicis muscle.