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.
How touch works
Touch receptors in the skin are nerve cells that inform the brain about tactile or touch sensations. There are two main types:
Thermoreceptors
These tell you about temperature. The two 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.
Nature of science
The Malpighian layer of the skin is named after Italian doctor Marcello Malpighi (1628–1694). He was a pioneer in using the microscope and has been described as a founder of microscopic anatomy. Most of his research from the universities of Pisa and Messina was published by the Royal Society of England. He became the first Italian to be recognised by this learned scientific society in 1668.
Activity ideas
Mystery box – using touch – students use only their sense of touch to put sandpaper samples in order from finest grade to coarsest grade.
Two-point discrimination – students explore how the receptors responsible for the sensation of light touch are distributed over the body.
Useful link
This article from the National Geographic website has interactives/animations and a video on the skin, skin stresses and the effects of ageing on the skin.
