A nociceptor (from Latin root 'nocere' that means to harm or hurt) is the sensory system apparatus that responds to harmful or potentially harmful chemicals or thermal stimuli. The harmful stimuli (for example, hot water on the skin or chili powder in the eyes) causes a 'threat' signal to be sent to the central nervous system (the brain and spinal cord). If the brain determines the threat to be valid it then responds with a pain signal to the specific body part so that the organism can attempt to eliminate the threat. This process is called nociception. There are two types of nociceptors - peptidergic and nonpeptidergic nociceptors.