Several types of primary afferent nociceptors exist, all of which normally respond maximally only to noxious stimuli (see Chapter 1). This response, known as nociception, consists of the emission of pain signals to the central nervous system, that is, to the brain and spinal cord. The reaction to the stimulus is processed as pain by the cortex, just like chemical and thermal responses. They respond to a specific stimulus. Some types of mechanoreceptors fire action potentials when their membranes are physically stretched. sensory receptor – a nerve ending that sends signals to the central nervous system when it is stimulated Sensory Receptors Chemoreceptors respond to chemicals in taste and smell and in internal changes. Chemoreceptors detect the presence of chemicals. Stimulation of nociceptors causes the sensation of pain.