What division of the human nervous system is responsible for maintaining body temperature?

The hypothalamus in the brain plays a primary role in regulating body temperature. When a person is exposed to a cold environment, the hypothalamus senses such a change, causing the body to undergo changes that conserve heat (blood vessels constrict, muscle cells contract involuntarily, a process referred to as shivering). Conversely, when one is exposes to excess heat, the hypothalamus also senses such an environmental change, and triggers physiological processes such as sweating and the dilation of blood vessels.

In fact it is not just nuclear fusion and fission that  can  transform  matter  (or mass)into energy. any time  energy  is produced, some small amount of  matter  or mass isconverted into energy.