Thus, a physical input can be things like sound, touch, heat, or light. The inputs that activate sensory neurons can be physical or chemical, corresponding to all five of our senses. Sensory neurons are the nerve cells that are activated by sensory input from the environment - for example, when you touch a hot surface with your fingertips, the sensory neurons will be the ones firing and sending off signals to the rest of the nervous system about the information they have received. For the spinal cord though, we can say that there are three types of neurons: sensory, motor, and interneurons. So just how many types of neurons are there? And how do scientists decide on the categories? For neurons in the brain, at least, this isn’t an easy question to answer. Just from looking down a microscope, however, it becomes very clear that not all neurons are the same. They are the fundamental units that send and receive signals which allow us to move our muscles, feel the external world, think, form memories and much more. Neurons are the cells that make up the brain and the nervous system.
