No matter what you feel like you've accomplished (or not) today, your body has been working really hard. Even if you've spent the day lying on the sofa, your body has been directing, overseeing, and facilitating hundreds of complicated functions, keeping you safe, comfortable, and making split-second decisions that benefit you without you giving them a conscious thought.
These automated bodily functions are the work of your nervous system—a network of neurons that transmit signals all around your body, telling your organs exactly what they should be doing and when. Most of these neurons—around 100 billion—are in your brain, and each of the thousands of types of neuron serves a specific purpose. Together, those specific purposes contribute to one overall objective: keeping your body safe, well, and comfortable. Here's an introduction to how your body manages to support itself automatically.