Touch
Skin, used as the sense organ of touch, forms a barrier between this world and you.
Image: Human skin
Our sense of touch allows us to receive information about our internal and external environments, making it important for sensory perception.
The first sense to develop in a human foetus is touch. At 8 weeks, a foetus responds to touch of the lips and cheeks, with other body parts responding by 14 weeks. Infants use touch to learn about the world around them and to bond with others – positive touch assists an infant’s healthy development.
Our skin
The skin is the largest organ in the human body and houses receptors that sense touch. The skin of an average adult, spread out, takes up the same space as a single blanket!
The skin doesn’t just clothe your skeleton and organs. It has several other functions:
It forms a protective layer keeping bacteria and fungi out.
It stops the body drying out (dessication).
Exposure to sunlight turns the skin into a vitamin D-producing organ capable of making protective oils. (Vitamin D is also important for healthy bones.)
It produces temperature-regulating sweat, which also helps rid the body of unwanted chemicals like salt.
Diagram of the human skin structure.
Image: Diagram of human skin structure
Your skin is made of layers of flat, stacked cells laid down into thin sheets. The three layers of the skin are the epidermis, dermis and hypodermis. Skin constantly renews itself by new skin cells pushing upwards, causing older cells to fall off.
Skin also contains nerves, sensory receptors, sweat and oil glands and hair follicles.
How touch works
Cross-section of human skin.
Image: Skin cross-section
Touch receptors in the skin are nerve cells that inform the brain about tactile or touch sensations. There are 2 main types:
Thermoreceptors
These tell you about temperature. The 2 structures thought to be used for temperature detection are:
end bulb of Krause, which detects cold
Ruffini’s end organ, which detects heat.
Mechanoreceptors
These tell your body about pushing/pulling forces and body movement and are responsible for translating these physical forces into nerve impulses. Included in this receptor group are:
Pacinian corpuscles, which detect deep-pressure touch and high-frequency vibrations
Meissner’s corpuscles, which are responsible for the detection of light touch and are found in the skin of the fingertips, lips, body orifices and nipples
Merkel’s discs, which provide information relating to pressure and texture and are found in areas like fingertip ridges.
The receptors change chemical, thermal or mechanical responses into electrical signals. The signals travel along axons (the extensions of nerve cells or neurons), which form pathways along which messages travel to areas of the brain that receive and interpret them. In the brain, we interpret sensations using our previous experiences and the properties of the receptors.