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THE NERVOUS SYSTEM

Has a doctor ever tapped on your knee with a small rubber mallet or checked your eyes with a light? Doctors use these tools to check the nervous system. The nervous system is very important. None of the other body system could work without its help.

Your brain is the control center of your nervous system. There are billions of nerve cells in your brain. Signal from thebrain direct your body´s activities.

Your brain receives information from all parts of your body. Messages from your body travel along nerves to the spinal cord. The spinal cord is a bundle of nerve tissue that runs through your backbone to your brain. The brain acts on information it gets from the body. Then it sends messages back out through the spinal cord.

Messages to and from the braintravel along nerve cells, or neurons. Groups of neurons are called nerves.

Messages from the brain travel down the guitar player’s spinal cord. They are signals that direct fingers how to move.
Brain
Spinal cord
Nerve
SKELETAL SYSTEM
Have you ever seen a skeleton? A skeleton may look strange, but the bones of the human body work together to do some very important jobs. Bones support yourbody and give it shape. They help you move, and some bones make blood cells. They also protect the organs inside your body. Your skull, for example, protects your brain from injury. Your ribs protect your heart and lungs.
A bone is a hard organ made up of connective tissue. The outer part is a hard, smooth, and strong. This part helps your bones support your body. It gives your body its shape.The bone is lined with spongy bone tissue, which has many open spaces. The center of many bones has marrow, tissue that makes red blood cells.
A place where your bones meet is called a joint. At a joint, muscles and bones work together to move a part of your body. Some joints open and close, like the hinges of a door. Your knees work this way. Other joints move in different ways.
The hard outerpart of a bone gives it strength. The marrow inside the bone makes red blood cells.
Blood vessels
Marrow

Bones give your body support, help you move, protect your organs, and make blood cells.
Skull
Humerus
Radius
Ulna
Pelvis
Femur
Tibia
Fibula
THE MUSCULAR SYSTEM
Your muscular system is made up of muscles that work together to carry out many jobs. A muscle is a body partthat’s made up of bundles of long fibers. Many muscles work with bones to help you move. Other kinds of muscles do other work.
Cardiac muscle makes up the walls of your heart. Cardiac muscle contracts and relaxes to help pump blood from your heart to the rest of your body. You don’t have to think about this action-your heart muscle works on its own.
Smooth muscle is found in the walls of your body’sorgans. Like cardiac muscle, smooth muscle works even though you don’t “tell” it what to do. It contracts and relaxes, which helps your stomach, intestines, and blood vessels do their jobs.
Skeletal muscles help you move. They work by pulling on bones. Because skeletal muscles can only contract, they work in pairs to move bones back and forth.
Muscles connect the bone of the upper arm to the bonesof the lower arm.
Skeletal muscles are made up of long fibers. These fibers, which may be up to 30 centimeters (12 IN.) long, are bundled together.
Skeletal muscles Works in pairs. One muscle in a pair pulls a bone in one direction. The other muscle pulls it in the opposite direction.
Triceps
Biceps
Quadriceps
Hamstring
Calf muscle

JOINTS
You have more than 230 joints in your body.Most of these places where bones meet are movable. They let your body change position.
In most joints, ligaments -which are tough bands of tissue-connect bones to each other. The muscles are connected to the bones by tendons, another type of tough connective tissue.
Depending on their shape, bones can fit together in different ways. Some joints, like those in your knees and elbows, move like...