Chapter 27.5 Daniela Torres

Concept check 27.5
1. Explain how muscles work in pairs in moving limbs.

Muscles work in pairs when moving limbs. As a muscle contracts, it pulls on the attached bone. When a skeletal muscle is contracting, there is an opposing muscle-one that is relaxed, but can still contract and pull the bone back in the opposite direction.

2. Identify the structures that make up a skeletal muscle. Include these terms: muscle fiber, fascicle, myofibrils, actin, myosin, sarcomere.
An skeletal muscle is made up of a bundle of parallel muscle fibers (a fascicle), along with a supply of nerves and blood vessels. Each muscle fiber is an elongated (long) cylindrical muscle cell that contains many nuclei. Inside each muscle fiber there are bundles of smaller units called myofibrils.Each myofybril is made up of repeating units called sarcomeres. Each sarcomere is made up of two kinds of filaments: actin and myosin.

Actin is the thin rope like structure rapped around the thick filament that is myosin. Both of these filaments work together and are responsible for muscle contraction.


3. Identify at least 3 organ systems involved in a handshake. Describe WHAT each system contributes to the handshake.
1. First, all the main coordination occurs in the brain when the eyes sense the presence of another person and sends signal to brain.
2. Later on, the information on the brain decides to initiate the handshake.
3. The other brain regions send out messages along the nerves to an array of muscles.
4.After the response consists of a series of relaxation and contraction of various muscles from the back, forearm, shoulder, wrist, and upper arm.
5. Finally many muscles amnipulate the 27 bones in the hand.
During this whole process the nervous system contributes by sending the signals to the brain of what is happening, how, and when and how to perform the response to the signal taken.
The circulatory system contributes to this process by providing a constant supply of oxygen and nutrients through the blood vessels to make the muscles move.
Finally, the intergumentary system senses the response(the final handshake) and sends this response to the brain. plus, it protects the inner strucutres of the hand needed to perform the hand shake initiallly.

4. Explain how actin and myosin interact as a muscle cell contracts.
Actin and myosin interact as a muscle cell contracts in the following way:
1. First myosin heads bind to thin filaments.
2. Later the myosin heads bends pulling the thin filaments towards the sarcomere.
3. Later on, ATP binds to each myosin head freeing it from the thin filament.
4. By this the myosin is free to attach to a new spot and further pull the thin filament along.
5.Filaments dont get shorter; they simply just overlap each other.
6. Consequently the sarcomere shortens.
7. This process continues until sarcomere contracts.
8.As the sarcomeres of many muscle fibers shorten, the muscle contracts.