The Sense of Touch: Hardly Noticed, But Key To Our Survival
Sense of touch is a bit different than the other 4 senses. Unlike the other senses, which are located at specific body parts, touch is a sense that is all over your body. Almost any part of the skin is able to sense touch. And although most of us take the sense of touch for granted, without it we would be in big trouble.
Sense neurons are located on the bottom skin layer called the dermis. Here there are nerve endings called sensory neurons. These neurons carry signals to the brain which are quickly processed into useful information then the body reacts if it needs to. Reaction involves signals from the brain traveling to the appropriate muscle neurons where the action will be taken, e.g. tightening your hand around a glass.
There are about 20 different types of sensory neurons. Some of them might sense cold, heat, pain, pleasure, etc. Pain and heat receptors are probably the most important. Without these you could suffer severe injuries if you didn't pull away from e.g. severe heat. In fact, this is so important that the body has developed a mechanism called the arch reflex, where signals don't even need to go to the brain for processing.
For example, if you touch something very hot the signal from the sensory neuron will travel only to the spinal cord. From there another signal will travel to the muscle neurons to cause you to pull your hand away. Arch reflexes almost always involve flexion of muscles, meaning the extremity is pulled closer to the body. This process is so well developed so that the brain does not need to get involved. Involving the brain would take more time and would lead to further injury.
Some areas of the body are more sensitive than others. For example, the corner of your elbow is not sensitive at all. Go ahead, pinch it and notice how it doesn't hurt. Where other parts can be more sensitive. Finger tips can be so sensitive so that the blind can read braille. The tongue is also very sensitive. If you have ever bitten your tongue you'll notice that the pain is extreme. However, the tongue is not very sensitive to heat or cold which is why many times you burn your tongue with something hot. The lips are much more sensitive to heat and cold so we test liquids first with our lips.
Touch is also vital for our health from a different perspective. As humans we need touch. Babies who do not receive enough touch may not live, or may develop psychological problems. Babies with more touch will grow to be healthier both physically and psychologically.