Muscular+System+HW1+MC

Muscular System SCI Human Biology - 1 Assigned: 9/29 Due: 9/30 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? There is smooth muscle, cardiac muscle, and skeletal muscle. Smooth muscle sustains prolonged contractions and does not fatigue easily. Cardiac muscles form the heart wall and allow fibers to interlock at intercalated disks. It relaxes completely between contractions, which prevents fatigue. Skeletal muscles support the body, help maintain a constant body temperature, assist movement in the cardiovascular and lymphatic vessels, and help protect internal organs and stabilize joints. 2. How do skeletal muscles work together to cause the bones to move? When a muscle contracts, it pulls on the tendons at its insertion, and the bone moves. They function in groups to make a particular movement. Muscles can only pull, they cannot push. Muscles work in opposite pairs. 3. Insert an image of the major muscles in the body like the one on page 231.

You will need to know the location and function of the following (write the function next to the name -- see page 231)

-Pectoralis major= brings the arm forward and across the chest - Deltoid= brings arm away form the side of body; moves arm up and down in front - Trapezius= raises scapula, as when shrugging shoulders; pulls head backwards. - Biceps Brachii= bends forearm at elbow - Triceps Brachii= straightens forearm at elbow -External oblique= compresses abdomen; rotation of trunk - Lattisimus Dorsi= brings arm down and backward behind the body - Gluteus Maximus= extends thigh back - Quadriceps femoris= straightens leg at knee; raises thigh - Gastrocnemius= turns foot downward, as when standing on toes; bends leg at knee.

4. Define myofibrils, sarcomeres, myosin, actin. Myofibril is a contractile portion of muscle cells hat contains a linear arrangement of sarcomeres and shortens to produce muscle contraction. A sarcomere is one of many units, arranged linearly within a myofibril, whose contraction produces muscle contraction. Myosin is one of two major proteins of muscle; makes up thick filaments in myofibrils of muscle fibers. Actin is also one of two major proteins of muscle; makes up thin filaments in myofibrils of muscle fibers. 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 sarcomere but not in the middle. Primarily, a thin filament consists of two intertwining strands of the 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?) The sliding filament model is the movement of actin filaments in relation to myosin filaments. During the sliding process, the sarcomeres shorten, even though the filaments themselves remain the same length. ATP supplies energy for muscle contraction. It’s the myosin filaments that do the work. Myosin filaments break down ATP, and their cross-bridges pull the actin filaments toward the center of the sarcomere.