How does the body's arrangement of nerve receptors for touch make the braille system possible

Human fingers are so sensitive because they are highly innervated with sensory receptors. The body is arranged so that areas requiring discriminative touch have more nerve receptors.

Human fingers have glabrous skin or skin without hair. Within glabrous skin, there are specific receptors that may differ from hairy skin. The specific receptor in the finger tips that allows for discriminative touch are called Meissner's Corpuscles.

Braille is a system of raised dots that can be read with the fingers by people who are blind and they can recognize the dots by their fingers which have touch receptors.

Sensory receptors perform various functions in our bodies. During vision, photo receptors respond to light intensity and color, but those people who are blind do not have functional photo receptors that is why they use their touch sense to recognize letters and words for reading. The technique is called braille system. Braille symbols are formed within units of space known as braille cells. A full braille cell consists of six raised dots arranged in two parallel rows each having three dots. These dots are touched by fingers and  touch sensors in fingers take signals to the brain which takes no time to respond and hence the letters are recognized by the reader.