Sense of touch: Skin is the sensory organ for touch and is also the largest sense organ. Our sense of touch allows us to feel light sensation like the touch of a feather as well as a heavy sensation like a stone falling on the toe. These sensations come from millions of microscopic simple sensory receptors located all over the skin and associated with the general sensations of contact or pressure, heat, cold, and pain. The receptors are located at different levels within the skin and distributed unevenly. Some parts of the body have a large number of these such as the finger tips, making them more sensitive. Structurally, these touch receptors are either free dendritic endings or encapsulated dendritic endings present in the skin (and other parts of the body). When stimulated, these transmit the sensation to the brain.
Given below is a list of some of these receptors present in the skin:
(i) Free or bare dendritic nerve endings are present throughout the epidermis taking an extensive branching or "zigzag" form. These respond chiefly to pain and temperature but some respond to pressure as well. The root hair plexuses, network of free nerve endings that surround hair follicles, are light touch receptors that detect bending of hairs.
(ii) Meissner's corpuscles are located in the papillary layer of the dermis just below the epidermis, which respond to touch our skin.
(iii) Pacinian corpuscles are scattered deep in the dermis and in the subcutaneous tissue of the skin. These are stimulated by deep pressure. These receptors are best suited to monitor vibrations, on-off pressure.
(iv) Ruffini's corpuscles respond to heat.
(v) Krause's corpuscles are excited by cold and are found in large numbers in the face and hands.
