 You may think that watching this video requires very little energy, but in reality your body is buzzing with activity. Your eyes and ears are sending signals to your brain that it processes so you can see and hear everything on the screen. At the same time, you are creating new memories, allowing you to remember what you are learning. But how does your body do this so quickly you barely know what's happening? The answer is through the action of billions of cells called neurons that work together to form your nervous system. The study of how neurons function and interact so we can see, hear, smell, taste, feel, think, and move is called neurobiology. Let's start with the basics. In 1888, a neuroscientist named Santiago Ramon y Cajal visualized one of the first neurons ever seen through a microscope and documented what he saw in several famous drawings. These pictures led to the classification and naming of the three main parts of the neuron, the cell body, the dendrites, and the axon. You can think of the dendrites as the inbox of the neuron, the cell body as the person reading the email and formulating a response, and the axon as the outbox. The dendrites are branch-like projections extending from the cell body through which the neuron gathers information from its environment, including other cells. The cell body houses the nucleus and many of the cellular organs known as organelles, which aid in processing incoming messages from the dendrites and regulating the production of outputs like proteins or other molecules. Lastly, the axon is a longer, less branched projection from the cell body from which the neuron sends outgoing signals to other cells. But how exactly does a signal received by dendrites travel all the way down a long axon so fast? The answer is electricity. Neurons are able to generate electrical signals that can rapidly travel through the cell, sometimes up to 120 meters per second, which is over 260 miles per hour. These signals are created by the movement of ions, a type of atom that carries an electrical charge across the cell membrane. This movement changes the electrical charge on the inside of the cell versus the outside of the cell, resulting in an electrical signal called an action potential. When an action potential reaches the end of an axon, it triggers the activation of electrically sensitive proteins. These proteins then facilitate the release of neurotransmitters, small molecules that neurons use to communicate with each other, into the tiny space where two cells meet, also known as synapse. Here, the neurotransmitters are detected by membrane proteins on the receiving cell, which initiates a specific action, the generation or cessation of an action potential. Through this process, billions of cells are able to talk to each other and form the complex network of interconnected neurons that make up the nervous system. The cells that make up the brain and spinal cord are collectively called the central nervous system, or CNS. The CNS is responsible for both sending information from and processing information sent back to the brain. All of the neurons outside of the central nervous system make up the peripheral nervous system, which is responsible for carrying out commands from the CNS, as well as sending information from the rest of the body and the environment to the CNS. So next time you watch a video, while all may seem simple and routine from the outside, you now know that a flurry of complex and well coordinated activity on the inside is responsible for all you see, hear, understand, and remember, including the colors, sounds, and the story you've just experienced.