Background Paragraph: When you go to the dentist to get a tooth pulled, you really don’t want to feel any pain. The dentist injects an anesthetic into your gum and it eventually becomes numb. One theory as to why anesthetics work deals with the movement of ions across the cell membrane. The anesthetic gets into the membrane structure and causes shifts in how ions move across the membrane. If ion movement is disrupted, nerve impulses will not be transmitted and you will not sense pain – at least not until the anesthetic wears off. 
Story: Two men in the Vietnam War needed to have their arms amputated. Unfortunately, the men were not able to be knocked unconscious for the operation. The doctor asked each patient if they wanted anesthetic injected into their arm or not. Marco replied that he wanted some, and Luke declined any anesthetic.
Which person's arm will be numb? Which person's arm will not be numb? Which person's ions will be able to move across the cell membrane? Which person's ions will not be able to move across the cell membrane? Whose nerve impulses will be transmitted? Whose nerve impulses will not be transmitted?