How does the nervous system get information about the external environment, the organs and the tissues?
Information about the conditions of the external and internal environments, like temperature, pressure, touch, spatial position, pH, metabolite levels (oxygen, carbon dioxide, etc.), light, sounds, etc., are collected by exact neural structures (each for each type of information) called sensory receptors. Sensory receptors are distributed throughout the tissues according to their exact roles. The receptors get that information and transmit them by their own axons or through dendrites of neurons that connect to them. The information reaches the central nervous system that interprets and uses it to control and control the body.