As warm-blooded creatures, we use our own internal thermostat to keep us at a fairly even 37°C. That thermostat is located in an area of the brain called the hypothalamus and it constantly receives feedback from different areas of the body, with temperature updates.
When the hypothalamus is alerted of a drop in temperature it may first cause the hairs on our arms to stand up, trapping little pockets of air close to the skin. This process is called piloerection and is sometimes enough to insulate the body and bring the core body temperature back in line.
If these measures are not enough, the hypothalamus induces a more rigorous response, sending signals to skeletal muscles, causing them to contract and relax rapidly.
For our muscles to contract and relax in this way, they need to burn up some of the body’s energy reserves and this process releases heat, helping to warm the body back up again. Shivering acts a bit like a micro-workout for the body, an interesting analogy, as a recent study investigated if there is a correlation between the level of fitness and efficiency of shivering.
Preliminary results suggest that there is; the fitter you are the better you may be at shivering.
Our core body temperature is roughly 37°C (with small fluctuations depending on physical activity, time of day or even the way in which the temperature is measured).
Why is the body so keen to keep this particular temperature? It may be all down to fungi.
All living creatures are susceptible to infection by a number of different organisms, including fungi. It seems that we are less likely to be infected by a number of different fungal species, simply by being warm-blooded.
Research has shown that the number of fungal species that thrive on, and infect, an animal, decreases by 6% with every 1°C rise in temperature. Setting our thermostat to 37°C will keep those fungi away.
Of course, we don’t only shiver in response to the cold, there are other things that give us the shakes, such as fever or nerves. It seems a bit counterproductive to shiver when our body temperature soars with a fever but it is due to an adjustment in the body’s internal thermostat.
An infection in the body can reset our thermostat to a higher temperature.
Although our temperature is higher than normal, the body thinks it is low and the shivering response is set into action to bring our core temperature back up.
And 37°C is an ideal replication temperature for many microorganisms, but increasing the temperature of the body by just a degree or two can significantly impact their growth. That’s why our body’s response is to turn up the heat.
Why do we shake when nervous? This response is not triggered by temperature. Stress can induce a fight-flight or freeze response in the body.
The shivering we experience is a response to high levels of adrenalin, triggering rapid contraction of our muscles, priming them in preparation to fight, freeze or flee.