Final answer:
To cause a total loss of sensation, anesthesia must be applied to two consecutive spinal nerves because of overlapping sensory innervation regions.
Step-by-step explanation:
A total loss of sensation requires anesthesia of two consecutive spinal nerves. This means that to achieve a complete sensory loss in a given area, it is not enough to anesthetize just one spinal nerve due to the overlapping innervation from adjacent spinal nerves. As a result, blocking two adjacent nerves is necessary to ensure that all nerve fibers that might carry sensation from a particular area of the body are anesthetized.