Sensations in the skin are measured by tiny receptors at the ends of nerve fibers. There are several different types of receptor. Each type can detect only one kind of sensation, such a pain, temperature, pressure, touch and so on. These receptors are grouped together according to the importance of their function. There are large numbers in the hands and lips, for example, where the sensation of touch is very important. Your back, however, is far less sensitive as there are fewer receptors in that area of your body.