The sense of touch
The five senses that we have are the sense of smell, sight, hearing, taste, and touch. It’s understandable that the apparatus for four of the senses are located close to our brain. Our nose for the sense of smell, eyes for the sense of vision, ears for the sense of hearing, and mouth for the sense of taste. However the apparatus for the sense of touch is skin, which is the largest organ on our body.
Average adult has about 22 square feet of skin which weighs about 10 pounds. The sense of touch is detected by nerve endings called mechanoreceptors. The touch receptors are spread throughout the body in different densities. The presence of more touch receptors makes the area more sensitive. On human body, the tongue, lips and fingertips are the most sensitive parts. Mid-back is the least sensitive part. For example, “Each fingertip has more than 3,000 touch receptors, many of which respond primarily to pressure. The entire trunk, by contrast, has about as many touch receptors as a single hand.” (The Handy Guide to Touch by Elise Hancock.)
Here is a simple test to measure the sensitivity of touch on different body parts. It’s called two-point discrimination:
Bend a paper clip into the shape of a U with the tips about 2 cm apart. Make sure the tips of the U are even with each other. Lightly touch the two ends of the paper clip to the back of the hand of your subject. Your subject should not look at the area of skin that is being tested. Do not press too hard! Make sure both tips touch the skin at the same time. Ask your subject if he or she felt one or two pressure points. If your subject reported one point, spread the tips of the clip a bit further apart, then touch the back of the subject’s hand again. If your subject reported 2 points, push the tips a bit closer together, and test again. Measure the distance at which the subject reports “I feel two points.”
Try this test on the palm and back of the hand, fingertips, forearm, upper arm, shoulder, back, neck, cheek, forehead, lips, nose, legs, tips of the toes, soles and upper parts of your feet. Here are the results (Source: http://io9.com/5926643/10-fundamental-limits-to-human-perception-++-and-how-they-shape-your-world):
The sense of touch is the very first sense that is developed inside the womb when the nervous system is developed at around 8 weeks. That’s when the embryo becomes fetus. Fetus uses the sense of touch to feel inside the womb. After the baby is born, the baby continues to develop the sense of touch from the loving touch of the parents and all the physical surroundings.
The sense of touch can be improved by using more. For example, “Blind people develop great sensitivity to outward occurrences through their skin, especially their fingertips. Some can even distinguish colors with their touch.” (The Power of Touch by Phyllis Davis.) Although I think the latter statement is more from their intuition but it’s still amazing.
By the way, besides sensing the touch, skin also senses heat, produces sweat to control the body temperature, produces oil to lubricate and waterproof the surface, and grows hair (except on the palms of our hands and soles of our feet). Our skin does a lot. Please show your love to your largest organ by caressing your skin today.