The patient controls the degree of stimulation by turning a knob on a small switch box. When the stimulation is turned off, the numbness goes away immediately. Anesthesia works in a number of ways. Some anesthetic drugs block certain receptors. Others inhibit biochemicals that increase the nerve's likelihood of firing.
Some anesthetics have side effects.
Student Activity Test different methods to numb your sense of touch. Because pain and touch receptors on nerves are closely related, an area of skin more sensitive to touch will often be more sensitive to pain. More sensitive areas of skin will be able to tell one from two, even when the two are very close together. Less sensitive areas will require that the objects be widely spaced. A numbed area should become less sensitive.