1. Explain how muscles work in pairs in moving limbs.
Muscle and with other muscle have to work in pairs to be able of working. When one contracts the other relaxes and then they change.
Tendons makes the muscle impossible to move back to their original position.

2.Identify the structures that make up skeletal muscle
Muscle fiber: contains nuclei and is a long cylindrical muscle cell.
Bundle of tissue made of Myofibrils that are found inside the muscle fibers
microfibris are made from Sarcomere which is the unit that contracts in the muscle and has two kinds of filaments
Myosin: composed of proteins and have bump like projections. Thick
Acting: have a twisted structure and are composed of protein. Thin


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

First your eyes send signal to your brain, to what they are seen might happen
Second your brain sends signals to all the muscles for the movement of the arm.
And finally they start shaking, this includes the contradiction of the brain to shake while saying hi, the hand movement, the hand moves the shoulder, and many more .


4. Explain how actin and myosin interact as a muscle cell contracts.
Myosin heads attach to the actin, they get aligned together in the center called the sacromere. This causes the muscle to contract while the other muscle relaxes, means that the myosin release from the actin of ATP.