CONCEPT CHECK 27.5

1. Explain how muscles work in pairs in moving limbs.
Muscles cannot push only pull, so it works together with a pair. When a muscle is contracting, its opposing muscle is relaxed. This muscle has to contract and pull, so that it moves to the opposite direction. Ex) Biceps and triceps. When Biceps are contracted, triceps are relaxed, And vice verse.

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. (cylindrical shape)
Myofibrils: Found inside a muscle fiber. Unit of muscle fiber made up of smaller units that contract (sarcomeres)
Sarcomere: A myofibril are repeating units called sarcomeres. Unit of contraction in a muscle fiber. Has 2 type of filaments, thin and thick.
Actin: The thin filament of sacromere. Composed of protein. Twisted thin filament in a muscle fiber.
Myosin: The thick filament of a sacromere. Composed of protein. 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.
1st. Your eyes see the person, and send a message to your brain. The thinking side initiates the handshake, and sends message to muscles. There are coordinated contraction and relaxation in muscles: your back, shoulder, upper arm, forearm, and wrist. The muscles manipulate the 27 bones in your hand into place.

4. Explain how actin and myosin interact as a muscle cell contracts.
Myosin heads first attach to the thin filaments. Myosin heads bend, and pulls thin fillament in sacromere. ATP releases myosin head from thin filament. Myosin head is now free to attach at a new spot and further pull the thin filament along.

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