Grade by Grade
B. Life Systems · Human Organ Systems

The Nervous System: The Body's Control Centre

B2.1 B2.2 A1.2 A1.4About 45 minutes
Learning goals
  • I can name the parts of the nervous system and describe what each one does.
  • I can describe the jobs of three main parts of the brain.
  • I can explain how messages travel through nerves and what a reflex is.
  • I can measure my reaction time with a fair test.

Words to know

nervous system
The brain, spinal cord and nerves. It controls the body and senses the world.
neuron
A nerve cell. Neurons carry messages as tiny electrical signals.
nerve
A bundle of neurons that carries messages between the body and the brain or spinal cord.
spinal cord
A thick bundle of nerves that runs down your back, inside the backbone.
cerebrum
The largest part of the brain. It handles thinking, memory, the senses and movements you choose to make.
cerebellum
A part at the back of the brain that controls balance and coordination.
brain stem
The part that joins the brain to the spinal cord. It controls breathing and heartbeat.
reflex
A fast, automatic reaction that happens without you thinking about it.

Catch!

Someone tosses you a ball. In less than a second, your eyes see it, your brain figures out where it's going, and your arm and hand muscles move to catch it. All of that is controlled by your nervous system, your body's control centre.

A brown leather baseball glove with a baseball resting in its pocket, lying on green grass.
Catching a ball takes teamwork: your eyes send messages to your brain, and your brain sends instructions through nerves to your hand muscles. AI-generated image

Parts of the nervous system

  • Brain. Inside your skull. It receives messages, makes decisions and sends instructions.
  • Spinal cord. A thick cable of nerves that runs from the brain down your back. The bones of your backbone (vertebrae) protect it.
  • Nerves. They branch out from the brain and spinal cord to every part of your body, even your fingertips and toes.

Nerves are made of nerve cells called neurons. Neurons pass messages along as tiny electrical signals, very, very fast.

There are two main kinds of messages:

  • Sensory nerves carry messages to the brain from your senses (eyes, ears, nose, tongue, skin).
  • Motor nerves carry messages from the brain to your muscles, telling them to move.
brainspinal cordnervesnerves
The nervous system: brain, spinal cord and nerves reaching the whole body. (Simplified: real nerves branch much more.)
Part of the brainWhereMain jobs
cerebrumthe large top partthinking, learning, memory, the senses, movements you choose
cerebellumlower back of the brainbalance and coordination (smooth, steady movements)
brain stembottom, joins the spinal cordbreathing, heartbeat, and other things you don't think about
Three main parts of the brain.

Reflexes: faster than thinking

If you touch a hot pot, you pull your hand away before you even feel the pain. That is a reflex.

The sensory message from your hand goes to your spinal cord, and the spinal cord sends a message straight back to your arm muscles: "Pull away!" The message reaches your brain a moment later, and then you feel "Ouch!" Reflexes protect you from harm.

Other reflexes: blinking when something flies at your eye, sneezing, and your knee kicking when a doctor taps just below your kneecap.

hot potarmmusclebrainspinalcord1. sensory nerve: "HOT!"2. motor nerve: "Pull away!"3. "Ouch!"a momentlater
A reflex: (1) a sensory nerve carries the message from your hand to the spinal cord; (2) the spinal cord sends a message straight back along a motor nerve to your arm muscle; (3) the message reaches the brain a moment later, and then you feel "Ouch!"

Protect your control centre

Your skull protects your brain, but a hard hit can still cause a concussion, an injury to the brain (you learned about this in Grade 3 Health). Wear a properly fitted helmet when biking, skating, skiing or snowboarding, and sit out and tell an adult if you hit your head.

Worked example

Let's measure reaction time: the ruler drop

How quickly can Aiden catch a falling ruler?

  1. Set-up: Aiden rests his forearm on a table with his hand over the edge, thumb and pointer finger open about 3 cm apart. His sister holds a 30 cm ruler so the 0 mark is level with the top of his fingers.
  2. Test: without warning, she drops the ruler. Aiden catches it as fast as he can. He reads the number just above his thumb.
  3. Five trials: 12 cm, 10 cm, 11 cm, 9 cm, 8 cm.
  4. Average: add them: 12 + 10 + 11 + 9 + 8 = 50. Divide by the number of trials: 50 ÷ 5 = 10 cm.
  5. What it means: a smaller distance means a faster reaction. The message went eye → brain → spinal cord → nerves → hand muscles.

Aiden's average catch distance is 10 cm. Doing several trials and finding the average makes his result more reliable.

Just for fun

Why is a neuron invited to every party?

Because it has such great connections!

Hands-on activity

Reaction-time investigation

You need: a 30 cm ruler, a partner, paper and a pencil.

  1. Question: Is my reaction faster with my writing hand or my other hand?
  2. Predict which hand will be faster and why.
  3. Do the ruler drop 5 times with your writing hand. Record each distance.
  4. Do it 5 times with your other hand.
  5. Find the average for each hand.
  6. Keep it fair: the same person drops the ruler, the 0 mark always starts at the top of your fingers, you sit the same way each time, and the dropper doesn't warn you.
  7. Make a table and write a conclusion. Was your prediction supported?

Extra: try again after practising 10 times. Does practice change your reaction time?

Grown-up note: this is a safe activity; just make sure the ruler is dropped, not thrown.

Your turn

1

What are the three main parts of the nervous system?

2

What protects the spinal cord?

3

Which part of the brain controls your balance?

4

Which part of the brain controls breathing and heartbeat?

5

What is a reflex? Give an example.

6

Ruler drop trials: 14, 12, 13, 11, 10 cm. What is the average?

7

Do sensory nerves carry messages to the brain or from the brain?

More practice: warm-up

1

What is a nerve cell called?

2

What protects your brain?

3

What is the largest part of the brain?

4

In the ruler drop, does a smaller number mean a faster or slower reaction?

5

Which body system is the control centre?

More practice: on your own

1

Describe the path of messages when you see a ball and catch it.

2

Why is a reflex faster than a movement you think about?

3

Why should you do 5 trials of the ruler drop instead of 1?

4

Riding a bike needs balance. Which part of the brain is working hard?

5

Why should you wear a helmet when you skate or bike?

Challenge

1

Jada's average catch with her writing hand is 9 cm, and 13 cm with her other hand. What can she conclude? What else might affect the results?

2

A person's spinal cord is badly injured in the middle of their back. Why might they be unable to move their legs?

3

You are asleep, but you keep breathing and your heart keeps beating. Explain why.

Check your understanding

Quiz

1.

Which is not part of the nervous system?

2.

Which part of the brain controls balance and coordination?

3.

Motor nerves carry messages...

4.

Pulling your hand away from a hot stove before you feel pain is a...

5.

Ruler drop results: 8, 10, 12 cm. The average is...

6.

What protects the spinal cord?

For parents and teachers

Big idea: the nervous system (brain, spinal cord, nerves) senses, decides and controls. Neurons send electrical signals. Reflexes go through the spinal cord for speed.

How to help at home:

  • Be the ruler dropper. Don't give hints about when you'll let go.
  • Help your child add and divide to find the average (Grade 5 math).
  • Talk about helmet use for winter sports and biking.

Common difficulties:

  • Thinking a smaller ruler number means slower; it means faster.
  • Thinking the brain controls everything consciously. The brain stem works automatically, and reflexes use the spinal cord.