When the brain receives the message that the environment around the body is very cold, the temperature signal begins in neurons of the

Skin

The thermo-receptor neurons, which is found in the skin is responsible in sending signals to the brain that the outside environment is very cold. This information will undergo processing in the hypothalamus of the brain that produce different responses so the body can cope with the changes in body’s temperature. 

When it is cold, the body response by vasoconstriction where the arterioles gets smaller to reduce blood from going to the skin, keeping the core warm. Moreover, rapid contraction and relaxing of skeletal muscles through shivering will produce heat by respiration. Then, hairs on skin stand up and body will curl up to make surface area smaller allowing the body to keep warm.

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