The source of all those 1s and 0s is, of course, the brain's billions of neurons. When a neuron gets an incoming stimulus at one end--for example, photons strike the retina, which sends that visual information to a nearby neuron--an electric pulse travels the neuron's length. Depending on the
signals it receives, a neuron can crackle with hundreds of these impulses every second. When each impulse reaches the far end of the neuron, it triggers the cell to dump neurotransmitters that can spark a new impulse in a neighboring neuron. In this way, the signal gets passed around the brain like a baton in a footrace. Ultimately, this rapid-fire code gives rise to electrical impulses that travel along nerves that lead out of the brain and spread through the body, causing muscles to contract and relax in all sorts of different patterns, letting us blink, speak, walk, or play the sousaphone.