How Does the Sense of Touch Work?
“Your skin contains more than 4 million sensory receptors [mechanoreceptors] that are especially concentrated in the fingers, tongue, and lips. These nerve endings are sensitive to touch, pressure, temperature [thermoreceptors], and pain [pain receptors]. They gather sensory information and relay it through specific nerve bundles back to the central nervous system for processing and possible reaction. For instance, when you accidentally touch something hot, sensory responses in your fingertips travel quickly back to the brain, which immediately coordinates the protective response that makes you withdraw your hand in a hurry!” (source http://kidshealth.org/…/…us_system_p4.
Touch is actually a grab bag of various somatic senses, including the sensations of temperature, pressure, and pain, kinesthetic senses which give us a conception of our body in space (proprioception), and visceral senses such as stomach aches or nausea. Touch information is processed in the postcentral gyrus, corresponding roughly to the top middle area of the brain. The postcentral gyrus, or parts of it, are often referred to as the primary somatosensory cortex. This area gets more direct sensory input information than any other in the brain. Touch is one of the most primitive and universal of sensory apparatuses in the kingdom of life, alongside that of smelling. Almost all animals use touch to navigate complex environments, appraise their immediate surroundings, and detect the presence of food. In humans, much of the somatosensory cortex is devoted to processing touch signals from the hands and face – about 90%. Our touch senses in these “sensory hot spots” is correspondingly sensi
While your other four senses (sight, hearing, smell, and taste) are located in specific parts of the body, your sense of touch is found all over. This is because your sense of touch originates in the bottom layer of your skin called the dermis. The dermis is filled with many tiny nerve endings which give you information about the things with which your body comes in contact. They do this by carrying the information to the spinal cord, which sends messages to the brain where the feeling is registered. The nerve endings in your skin can tell you if something is hot or cold. They can also feel if something is hurting you. Your body has about twenty different types of nerve endings that all send messages to your brain. However, the most common receptors are heat, cold, pain, and pressure or touch receptors. Pain receptors are probably the most important for your safety because they can protect you by warning your brain that your body is hurt! Some areas of the body are more sensitive than
The body has a number of receptors that monitor outside and inside conditions. One of those receptors is a pressure receptor, sensitive to touch. They are not distributed uniformly on your skin. They are most dense on your fingers and lips, least dense on your back. In addition, since there are more receptors than skin nerves that go to the brain, a number of these touch receptors feed into a single sensory nerve. The area that the sensory nerve gets its input from is called a receptive field. Thus pressure from a pencil point on the skin will cause the same sensation within a single receptive field. If you want to see how this works, get a person, apply a pencil point on their skin (let’s say on one finger) while they are not looking, and then ask them to point out the spot you placed the pencil. Do that for a spot above their elbow as well. You will see quite an error in trying to locate the elbow spot, but some accuracy with the finger placement.