Touch is the sense that gives us notice of contact with an object. It also is called the tactile sense. We learn the shape and hardness of objects through this sense. Touching an object can give rise to feelings of warmth, cold, pain, and pressure. Free nerve endings in the tissue give the sense of pain. Touch, warmth, cold, and pain also are called cutaneous senses.
There are several kinds of touch organs, called tactile corpuscles, in the skin and the mucous membranes. One kind of touch organ is found near hairs, another kind in hairless areas, and still another kind in deeper tissues. The sensation occurs when an object comes in contact with the sense organs and presses them out of shape, or touches a nearby hair. Nerves from the organs then carry nerve impulses to the brain.
Touch is more sensitive in some parts of the body than in others. This difference is due to the fact that the end organs for touch are not scattered evenly over the body, but are arranged in clusters. The feeling of pressure is keenest where there are the greatest number of end organs. It is most highly developed on the tip of the tongue, and is poorest on the back of the shoulders. The tips of the fingers and the end of the nose are other sensitive areas.
The end organs for warmth, cold, and pain also are distributed unevenly. This can be discovered by running a pointed metal instrument over the skin. The instrument is colder than the skin, but it feels cold only at some points. At other points, the instrument is felt simply as pressure.
