How Does My Brain Send Messages to My Body?

Your brain sends many different kinds of messages to your body. Some you need to “think” about – like messages to move your fingers when you tie your shoes, or messages to pump your legs faster when you speed up your bike. These are called “conscious” commands or messages. They come from your brain’s cerebral cortex (the upper surface of your brain that’s covered with twisting lines – just like they show in the horror movies.)

Your cerebral cortex is made of millions of cells, called neurons, that “talk” to one another by passing on electrical and chemical messages. Neurons are so small that you need a microscope to see them, but they have branches that can stretch out for several inches (some can even stretch out for several feet !) Branches of neurons can reach down from the surface of your brain, out the bottom of your skull, all the way to your spinal cord. Your spinal cord, which is also made of neurons and their branches, is the main communication line between your brain and other parts of your body.

In your spinal cord, long branches of neurons (that have stretched down from your brain) can pass messages to other neurons, called spinal neurons. These spinal neurons have long branches, too, and they reach out of your spinal cord to carry messages to the muscles of your body. A special chemical, called acetylcholine, passes from the branches of spinal nerves to your body’s muscle cells and makes them contract. This makes your muscles move.

Let’s follow a “movement” message from your brain to see how the message chain works.

Say, for example, that you want to bend your right arm. The message for this comes from the left side of your brain (since each side of your brain controls the opposite side of the body). In your brain, a special group of neurons gets “excited” and sends a tiny urge of living electricity down from your brain’s surface, out the bottom of your skull, and down your spinal cord. In your spinal cord (somewhere in our neck area) the electrical message passes to a spinal neuron. Branches of the excited spinal neuron then carry the message away from your neck area, past your shoulder, to the muscles of your right arm. Acetylcholine passes from the nerve branches to your muscle cells and makes them contract.

The message is received, and your right arm moves!

Now, what about the millions of brain messages that you don’t need to “think” about – messages to your lungs to keep them breathing, to your intestines to keep food passing through, to your muscles to keep you standing against the pull of gravity. Even to your whole body when it’s time to sleep. These “unconscious” messages come from deeper parts of your brain, not from its surface. They come from places like your hypothalamus, a very important part of your brain that’s found behind your eyes. Your hypothalamus has neurons that keep track of body temperature and blood pressure. Neurons in your hypothalamus can start a chain of messages to your skin to make you sweat (this cools your body). They can also send messages to your blood vessels to change your blood pressure.

Other unconscious messages come from groups of neurons found in your brain stem. Brain stem neurons control the rhythm of your breathing and the length of each breath. But what if you want to use the air in your lungs to talk or sing? Do you have to wait for your brain stem to give permission? Of course not! When you decide that you want to talk or sing, neurons in your brain’s “thinking” cortex take over control of breathing temporarily. Then, when you’re finished speaking or singing, breathing control returns to your brain stem centers – so you don’t need to “think” about every breath you take.

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