Your body is amazing. Did you know you have more than 200 bones and 600 muscles? Your nerves carry messages from your brain to make those muscles cooperate so you can stand up and move around. Your blood vessels could stretch all the way around the planet! White blood cells stand guard like soldiers waiting to attack any invader. Your heart, lungs, stomach, and other organs are at work 24 hours a day for your entire life. There are too many parts inside you to count, but they all work together to keep you alive. No machine is as complex as you are.
Take a deep breath. Feel how your chest swells. Lungs inside your body are filling up with air. Every time you breathe in, or inhale, your lungs fill up with air. When you breathe out, or exhale, your lungs empty out. You probably breathe about 20 times every minute. If you are running or playing hard, you might take 80 breaths a minute. What happens to all this air?
It goes to your lungs. Your lungs are like two big sponges inside your chest. Lungs are the body organs you use for breathing. All mammals, birds, reptiles, most amphibians, and even some fish have lungs.
Is memory important to you? How often do you think you use yours? Actually, you use it every moment of every day. You remember who you are, where you live, and what you are doing. Without memory, you could not survive!
There are three kinds of memory: sense memory, working memory, and long-term memory. Think of them as three connected rooms in which you store different kinds of memories.
The first kind of memory is sense memory. Everything you are sensing right now is stored here. Perhaps you feel the Sun on your face or smell the aroma of food.
Do you ever visit the doctor? Sometimes people visit doctors because they are not feeling very well. Sometimes people visit doctors for a physical examination, or checkup. Visits to doctors are part of medical care. Many other people also contribute to medical care.
WHAT DO DOCTORS DO?
Doctors try to diagnose, or figure out, what makes people sick. If you have a sore throat or a bad cough, the doctor examines you with a stethoscope. The doctor uses the stethoscope to listen to your heartbeat and to the sound your lungs make when you breathe.
How strong are you? Can your legs run fast? Can your arms lift heavy books? Your muscles make your legs run fast. Your muscles let your arms lift heavy books. Without muscles, you wouldn’t be able to move at all!
HOW DO MUSCLES WORK?
Muscles work by tightening and loosening. Tightening is called contraction. Loosening is called relaxing. Your nerves tell muscles when to contract.
Suppose you see a cookie on a table. You want to pick up that cookie and eat it. Your brain sends out a signal. Nerves carry the signal from your brain to your arm and hand muscles. The signal tells muscles in your arm to contract.