Receptors are the cells that detect the changes in chemical and physical conditions of external and internal environment of an animal. Main categories of sensory receptors include mechanoreceptors, thermoreceptors, pain receptors, chemoreceptors and photoreceptors. Stimulation of sensory receptors generates a nerve impulse that travels through the CNS (brain/spinal cord) where integration and interpretation of sensory information take place. This is followed by a relay of motor impulses from CNS to effector organ to generate the response according to the stimulus. If receptors are not working properly, the external stimulus won’t be able to stimulate receptors and no nerve impulse is generated. The result is that the body would not respond to changes in the surroundings.