Question

Why isn't your skin's sensitivity proportional to the size of the corresponding body part?

Answer 1

The skin’s sensitivity is not proportional to the size of the corresponding body part. This is because the parts of the skin that need to be most sensitive, like the fingertips and your lips, have more receptor cells in them than other, less sensitive areas. The density of receptor cells in the area determine its sensitivity. For each of the areas, the somatosensory cortex in the brain has a 'sensory map', with more space devoted to some areas of your body than others.