As humans, we really like breathing oxygen. That's because the cells in our body will die if they don't get oxygen to function in a reasonable amount of time. This tutorials describes how we use the lungs to exchange gasses between our blood and the atmosphere and how the oxygen is then pumped through the body by way of blood and the circulatory system.
Neurons are the primary way that our bodies transmit signals from one part to another quickly. In this tutorial, we'll explore the anatomy of a neuron and the mechanism by which a signal is actually transmitted through one.
Without muscles, we wouldn't be able to do much of anything. This tutorial begins to explore what muscle cells are and how they contract in order to move our bodies (or do things like breath and pump blood).