Human Body Temp Control -cold exposure

Let us consider the situation where the body is exposed to cold surroundings and the temperature of the core starts to fall below 37°C. The central sensor nerve cells now decrease the rate of nerve impulse generation. As a result of this, the brain sends messages to various muscles of the body causing them to shiver. Shivering is a rapid alternate contraction and relaxation of muscles and this generates heat. The heat is added to the core. In this situation, the muscles are acting like the heater in the room.

The brain also controls the amount of blood coming to the skin. This is done by constricting the blood vessels that penetrate the insulating fat layer and come to the surface of the body. When less blood reaches the skin the amount of heat lost from the core is reduced. Click on the "Low" button in the diagram below and watch what happens to blood flow and heat loss.

Another way in which the brain controls the loss of heat from the core is by causing the hairs on the skin to stand on end. The brain achieves this by activating tiny muscles at the roots of the hairs. The air which is trapped by the hairs becomes another layer of insulation. This mechanism is important in animals with a lot of fur.
However, in humans, it only produces "goose bumps" because they do not have much body hair.

Click on the "Low" button and watch what happens.

If the exposure to cold is prolonged, another slower process occurs. The brain increases the output of thyroid hormone into the blood stream from the thyroid gland in the neck. The thyroid hormone reaches all the cells of the body and increases their metabolic activity which increases heat production.