Muscular+System+NLL

//**Muscular System Chapter 12 pp 227-236 (New Unit called Move it)**//

1. What are the three types of muscles in the body and what is the function of each? Humans have three types of muscle tissue: smooth, cardiac, and skeletal. These tissues are called muscle fibers. Smooth muscle fibers are spindle-shaped cells, each with a single nucleus. Cardiac muscles form the heart wall. Its fibers are generally uninucleated, striated, tubular, and branched, which allows the fibers to interlock at intercalated disks. Skeletal muscle fibers are tubular, multinucleated and striated. They make up the skeletal muscles attached to the skeleton.

2. How do skeletal muscles work together to cause the bones to move? Skeletal muscles make bones move. Muscle contraction accounts not only for the movement of arms and legs but also for movements of the eyes, facial expressions, and breathing. The contraction of muscles at death, observed by Jason in the opening story, is called rigor mortis.

3. Insert an image of the major muscles in the body like the one on page 231.


 * Pectoralis major:** brings arm forward and across chest. Located in the chest.
 * Deltoid:** brings arm away from the side of the body; moves arm up and down in front. Located just below the shoulder.
 * Trapezius:** raises scapula, as when shrugging shoulders; pulls head backward. Located in the upper back.
 * Biceps brachii:** bends forearm at elbow. Located in the forearm.
 * Triceps brachii:** straightens forearm at elbow. Located in the forearm.
 * External oblique**: compresses abdomen; rotation of trunk. Located just above the hip.
 * Latissimus dorsi:** brings arm down and backward behind the body. Located in the back.
 * Gluteus maximums:** extends thigh back. Located in the butt.
 * Quadriceps femoris:** straightens leg at knee; raises thigh. Located in the thigh
 * Gastrocnemius:** turns foot downward, as when standing on toes; bends leg at knee. Located in the calve muscles.

4. Define myofibrils, sarcomeres, myosin, and actin Myofibrils are cylindrical in shape and run the length of the muscle fiber. Myofibrils are each about 1 um in diameter, which are the contractile portions of the muscle fibers. Any other organelles, such as mitochondria are located in the sarcoplasm between the myofibrils.

5. Describe the structure of a sarcomere's thick and thin filaments. A thick filament is composed of several hundred molecules of the protein myosin. Each myosin molecule is shaped like a golf club, with the straight portion of the molecule ending in a globular head, or cross-bridge. The cross-bridges occur on each side of a sacromere but not in the middle. A thin filament consist of two intertwining strands of protein actin. Two other proteins, called tropomyosin and troponin, also play a role.

6. Describe the sliding filament model and insert image (How does the sarcomere contract?) Muscles are stimulated, impulses travel down a T tubule, and calcium is released from the sarcoplasmic reticulum. Now the muscle fiber contracts as the sarcomeres, within the myofibrils, shorten. When a sarcomere shortens, the actin (thin) filaments slide past the myosin filaments and approach one another. This causes the I band to shorten, the Z line to move inward, and the H zone to almost or completely disappear. The movement of actin filaments in relation to myosin filaments is called the sliding filament model of muscle contraction. During the sliding process, the sarcomere shortens, even though the filaments themselves remain the same length. ATP supplies the energy for muscle contraction. Although the actin filaments slide past the myosin filaments, it is the myosin filaments that do the work. Myosin filaments break down ATP, and their cross-bridges pull the actin filaments toward the center of sacromere.