Video narration
How does seeing a cup turn into reaching for it? You see the cup, and messages from your senses travel through nerves to your brain. Your brain processes them and, with the rest of your nervous system, sends signals to your arm and hand muscles. But it doesn't send one command and stop. As your hand moves, fresh sensory messages help your brain adjust the reach. That's how you reach the cup: sensing, signaling muscles, adjusting as you move.