Why do we shake in cold?

Answer 1

Shivering is a bodily function in response to early hypothermia in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by expending energy. Shivering can also be a response to a fever as a person may feel cold, though their core temperature is already elevated.

Located in the dorsomedial portion of the hypothalamus near the wall of the third ventricle is an area called the primary motor center for shivering. This area is normally inhibited by signals from the heat center in the anterior hypothalamic-preoptic area but is excited by cold signals from the skin and spinal cord. Therefore, this center becomes activated when the body temperature falls even a fraction of a degree below a critical temperature level.

Answer 2

It is the bodys way of attempting to warm itself. The motion generates heat, tho not enough to really be effective. I much prefer a hot bath and a good glass of wine to warm me up ;-)

Answer 3

It is an involuntary action to create heat in the muscles.