The document discusses the human muscular system. It notes that humans have approximately 700 muscles making up 40% of body weight. Muscles come in two types - voluntary muscles like those in the arms and legs which are controlled consciously, and involuntary muscles like the heart which are not under conscious control. Muscles contract and relax to enable movement, with tendons connecting muscles to bones. Muscles require nutrients like oxygen and glucose to function properly and can grow in size through weightlifting but also deteriorate without use over time.

1. The Muscular System

2. You are strong!
• If all your muscles were working together, you
could lift about 20 cars!

3. Your body has about 700 muscles
Muscles make up
about 40% of your
body weight.

4. Muscles weigh more than fat
Who will sink and who
will float?

5. Muscle fiber under a
microscope.

6. Voluntary and involuntary muscles
The heart has involuntary
muscle because we cannot
control it.
Muscles in our arms and
legs are voluntary and are
skeletal muscles.

7. Nerve cells called motor neurons
control muscles from signals from the
brain.

8. Massage
Massage is good
for your muscles
and body, and
can make you
feel relaxed and
happy.

9. Massage your pectoralis minor
If you type a lot on a
computer, or ride a
motorcycle a lot, this
muscle can get very
tight.

10. tendons
Tendons connect muscle to bone.

11. Your muscles need oxygen and glucose (sugar).

12. Why do our muscles “burn” when we
exercise a lot?
• Lactic acid in your muscles causes that pain.
“Hitting
the wall”
happens
when you
have no
glycogen.

13. Muscle cramps
Muscle cramps can have
many causes, such as
dehydration, not enough
blood flowing to the
muscle, or being tired.

14. Muscles move by contracting and
relaxing

15. To take one step, you use 200 muscles.

16. Muscles cannot push, they can only
pull.
When you push
something, it’s because
another muscle is
pulling.

17. The largest muscle in your body is your
gluteus maximus. Your butt!

18. When you’re cold, your muscles
contract involuntarily.
He is shivering.

19. You can make your muscles grow!
When you lift weights,
you tear your
muscles. When they
heal, they grow back
stronger and bigger.
It takes a long time to grow
muscles.

20. But they can shrink too. This is muscle
atrophy.
This woman broke her
leg, so she could not
use her right leg for a
long time.
Her right leg got
smaller.

21. Your muscles need protein

22. Muscles usually work together with
other muscles, not alone.

23. Muscular Dystrophy
A genetic disease
that causes muscles
to deteriorate.
Exercise and therapy
can help.

24. Questions
• What nutrient do we need to build muscle?
• What is an example of an involuntary muscle?
• What connects muscle to bone?
• About how many muscles do you have in your body?
• What kind of energy does your muscles need?
• What do your muscles do when you are really cold?
• What kind of exercise can make our muscles grow?
• What is the largest muscle in your body?
• What happens if you don’t use your muscles?