Explain how muscles work in pairs in moving limbs.

As one muscle contract the other muscle relaxes. Since muscles cannot push, only pull, and opposing motion is needed to return the bone to its original position.

2. Identify the structures that make up a skeletal muscle. Include these terms:
muscle fiber, fascicle, myofibrils, actin, myosin, sarcomere.

Muscle fiber: Long muscle cell that contains many nuclei.
Myofibrils: unit of muscle fiber made up of smaller units that contract (sarcomeres)
Sarcomere: unit of contraction in a muscle fiber Has 2 type of filaments, thin and thick.
Actin. Twisted thin filament in a muscle fiber.
Myosin: The thick filament of a sacromere. Has bump- like projections. called myosin heads.

3. Identify at least 3 organ systems involved in a handshake. Describe WHAT each system contributes to the handshake.

First your eyes sense a person near and sends a message to your brain. The thinking part of your brain decides to initiate the handshake. The other regions of the brain sends a message though your nerves to the muscles. The response are coordinated contractions and relaxations in the muscles of the back, shoulder, forearms, upperarm and wrist. These muscles lift and extend the right bones in the correct sequence to extend the hand. At the end many muscles manipulate the 27 bones in your hand into place.

4. Explain how actin and myosin interact as a muscle cell contracts.

Myosin heads with the thin filaments interact to make muscle contraction. IN a mini contraction myosin heads first bind to thin filaments, then the myosin head bend pulling the thin filaments to the center of the sacromere, the ATP binds to each myosin head relicing it from the filament.