1. How Muscles and Bones Interact

2. Preview: Make the Connection
Nerves
Tendons
Blood Vessels
Opposing Muscles

3. Nerves
Nerves transmit information from the brain, telling muscles when to contract, extend, or relax. Nerves are sent from our brain and also allow our brain to respond to senses which we may touch, taste, smell, hear, or see. Have you ever quickly tensed your muscles because you were scared or surprised by something? This is an example of your nerves at work!
Nerves of the Upper Arm

4. Tendons
Tendons are a form of tough connective tissue which joins skeletal muscle to bone. They are attached in a precise way, which allows them to pull on bones like levers. The muscles provide the force to move the bone, but the tendon does the pulling! Flex your arm and you will see your tendons pulling your forearm up, while your muscles provide the needed supporting strength.

5. Blood Vessels
Blood vessels keep muscles oxygenated and remove waste. As blood circulates through the body, oxygen that we breathe in is carried to muscles and organs throughout the body. As the blood returns, it carries with it waste such as lactic acid. Did you feel the burn in your legs after the wall-sit competition? That is a result of blood circulation slowing and being unable to keep up with lactic acid removal.

6. Opposing Muscles
Opposing muscles work like a choreographed partnership to move your limbs back and forth. As one muscle contracts (tightens), the opposing muscle releases (stretches). Take a look at your arm again. Flex your arm and watch as your biceps tighten and your triceps simultaneously release.