As an organ the skin has the following simplified functions:
- Passive and active protection
- Temperature regulation
- Sense organ for touch, temperature and pain
- Some respiratory functions
- Organ of expression
- Secretion of sweat
We are interested in the secretion of sweat at the palms of the hands. The structure of the skin is roughly as follows:
- Epidermis (cuticle) This layer is seen on the surface of the skin. It is made up of cells which are stacked on top of each other. They develop at the bottom and rise to the top, where they are shed from the surface as dead cells. So this layer is constantly renewing itself, the live cells changing into dead, hard, flattened cells. It contributes to almost all of the skin conductance.
- Dermis (sclera) The dermis consists mostly of connective tissue and is much thicker than the epidermis. It is responsible for the skin's pliability and mechanical resistance and is also involved in the regulation of the body temperature. The dermis supplies the epidermis with nutrients. It contains sense organs for touch, pressure, pain and temperature, as well as blood vessels, nerve fibres, sebaceous and sweat glands and hair follicles.
- Subcutis The subcutaneous layer below the dermis consists of loose connective tissue and much fat. It acts as a protective cushion and helps to insulate the body by monitoring heat gain and heat loss.
The top epidermis layer contributes the most (99.9%) to skin conductance compared to dermis and subcutan layer.
Sweat glands are found in almost every part of the skin, forming tiny coiled tubes embedded in the dermis or subcutaneous fat. The eccrine glands produce sweat - a mixture of water and salts which conducts current well. Sweat plays an important part in regulating the temperature of the body by cooling it by evaporation of water from the skin. It also provides a useful natural method of removing waste products (toxins) from the body. The tiny ducts of the eccrine glands pass through the dermis and epidermis and empty directly on to the skin.
On the inside of the palms and the soles of the feet we have about 3,000 glands per square inch, about 15 times more than on the rest of the body, roughly 2 to 3 million over all. The density on the palms and soles is one reason that only there we can get a good signal.
The other reason why only the activity of the glands in the palms and soles of the feet creates a good signal is that it is an expression of activity of the vagus nerve and as such an expression of psychological or mental activation. Sweat glands on the rest of the body are more controlled by temperature regulation instead of mental activity. In the context of an office, activation of the hand sweat glands is usually an expression of stress. |
