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Of the three motions, the deltoid acts most powerfully in abduction. The C5 neurologic level supplies sensation to the lateral arm from the summit of the shoulder to the elbow. The purest patch of axillary nerve sensation, pictured here on the right, lies over the lateral portion of the deltoid muscles. This localized sensory area within the C5 dermatome is useful for indicating specific trauma to the axillary nerve, as well as general trauma to the C5 nerve root.