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The Brain Sends Messages Through Your Nerves · Sensing and Responding · 4-LS1-2 · nervous system

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The Brain Sends Messages Through Your Nerves

with Medi

Medi stands in a bright gymnasium, catching a bouncing ball mid-air and grinning, while glowing lines trace from her fingertips up her arm toward her brain to show signals traveling.

Explain how the brain sends signals through nerves to control body movements.
Identify the brain, spinal cord, and nerves as the three main parts of the nervous system.
Describe how a signal travels from the brain to a muscle to cause movement.
Compare how fast nerve signals travel compared to ordinary messages like a spoken word.
Predict what could happen if a nerve signal between the brain and a muscle were blocked.

Key terms

brain: the body part that thinks and decides
nerve: a tiny wire that carries body signals
spinal cord: the big nerve bundle in your back
signal: a fast message your body sends inside
nervous system: your brain, spinal cord, and all nerves

Your Body's Messengers

Your nervous system has three main parts. They are your brain, your spinal cord, and your nerves. The brain is the boss. The spinal cord is a thick bundle of nerves inside your backbone. Tiny nerves branch out everywhere, all the way to your fingers and toes. Together they carry fast messages around your whole body.

How Signals Move You

When you want to move, your brain sends a signal. The signal zooms down your spinal cord and along your nerves to a muscle. The muscle then squeezes and you move. These signals are super fast, racing about 100 meters every second. That is why you can catch a ball or wave hello in the blink of an eye.

Worked examples

How do you wave hello to a friend?

Your brain decides to wave hello.
Your brain sends a signal down your nerves.
Your arm muscles get the signal and squeeze.
Your hand lifts up and waves.

Answer: The brain sends a nerve signal to your arm muscles, and they wave.

Hey there! I'm Medi, and I want to show you something amazing happening inside you RIGHT NOW. Your body has a super-fast messaging system called the nervous system. It has three main parts: your brain, your spinal cord (the thick bundle of nerves inside your backbone), and billions of tiny nerves that branch out everywhere — all the way to your fingertips and toes. Here's how it works. Imagine you decide to pick up a cold ice cube sitting on the table. Your eyes send a signal — like a tiny electrical spark — up through your nerves to your brain. Your brain reads the message in a split second and sends a signal back down through your spinal cord and arm nerves that says: "Hand, grab that cube!" Your muscles squeeze and — got it! Nerve signals travel about 100 meters per second. That's faster than a race car! A spoken word travels through the air much slower than that. Your nervous system is one of the fastest communication systems on Earth. Every move you choose to make — blinking on purpose, waving hello, kicking a soccer ball — starts with a signal from your brain traveling through your nerves to your muscles. Even your feelings, like noticing something is hot or cold, are nerve signals rushing to your brain so you know what to do. Hint: Think of nerves like telephone wires connecting your brain to every part of your body. The brain is the boss sending the calls!

Activity

Put these steps in the correct order to show how your brain helps you pick up an ice cube.

Practice

What are the three main parts of the nervous system?

What carries fast messages from your brain to your muscles?

Common mistakes to avoid

Muscles move all by themselvesMuscles need a nerve signal from the brain before they can move.
Nerve messages are slowNerve signals are very fast and race through your body quickly.

Check your understanding

What is the job of the nerves in your body?

Maria sees a cold ice cube on the table and decides to pick it up. Which path does the nerve signal travel?

Your friend says that muscles move on their own without any message from the brain. Is your friend correct?

Nerve signals travel about 100 meters per second. How does that compare to a spoken word traveling through the air?

Recap

Your nervous system has a brain, a spinal cord, and lots of nerves. The brain sends fast signals through nerves to your muscles so you can move and feel.

Reflect

Think about a fast move you made today using nerves!