Nervous system plays a vital role in communication with the external and internal environment. The sensory receptors take stimuli and send it to the brain by the sensory nerve. Respective part of brain analyses this, and motor nerve carry the instruction to the muscle. For example, when we touch a hot plate, we pull back our hand because the thermoreceptors present on our skin sends a signal of pain to the brain. This was an example of communicating with the external environment. Another example is maintaining body temperature. During fever, the temperature of our body increases due to the release of certain pyrogenes.