Eli5: How can we move almost any muscle the time we want? How does the brain knows it’s that specific muscle that you want to move?

Question

Like, I can be there just sitting and think. “Now I’m gonna move my middle finger”, and just do it, no reason at all. How does the brain know what muscle is each, how does a signal is determined to make you move the finger you want? Does the brain have a “map” or something of every muscle in your body?

In: Biology

Answer 1

You are exactly right that there is a map in the brain. If you look up images of “motor cortex homunculus” you can see a diagram showing which parts of the brain control which areas of the body. The individual neurons in the brain connect like wires through other nerves in the spinal cord which eventually go out to several muscle cells right next to each other. When the neuron fires, it causes chemicals to release that cause the muscle cells connected to it to contract. If the brain fires off a signal in all the neurons going to, say, the biceps, then the entire biceps will contract