Muscular+System+MV

Molly Vaughn 29 September 2008 Human Biology

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? - The three types of muscles in the body are the smooth muscle, the cardiac muscle, and the skeletal muscle. The smooth muscle fibers are spindle-shaped cells, each with a single nucleus. The cells are usually arranged in parallel lines, forming sheets. Striations are seen in the cardiac and skeletal muscle but not in the smooth muscle. Smooth muscle is located in the walls of hollow internal organs, and it causes these walls to contract. Contraction of smooth muscle is involuntary, occurring without conscious control. Although smooth muscle is slower to contract than skeletal muscle, it can sustain prolonged contractions and does not fatigue easily. Cardiac muscle forms the heart wall. Its fibers generally uninucleated, striated, tubular, and branched, which allows the fibers to interlock at intercalated disks. The plasma membranes at intercalated disks contain gap junctions that permit contractions to spread quickly throughout the heart wall. Cardiac fibers relax completely between contractions, which prevents fatigue. Contraction of cardiac muscle is rhythmical; it occurs without outside nervous stimulation and without conscious control. Thus, cardiac muscle contraction is involuntary. Skeletal muscle fibers are tubular, multinucleated, and striated. They make up the skeletal muscles attached to the skeleton. They run the length of the muscle and can be quite long. Skeletal muscle is voluntary because we can decide to move a particular part of the body, such as the arms and legs.

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 expression, and breathing. The contraction of muscles at death is called rigor mortis.

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: The pectoralis major is located in the chest and it brings the arm forward and across the chest. Deltoid: The deltoid is located in the upper arm and it brings the arm away from the side of the body; moves arm up and down in front.

Trapezius: The trapezius is located in the shoulder and it raises scapula, as when shrugging shoulders; pulls head backward.

Biceps brachii: The biceps brachii are located in the arm and it bends forearm at elbow.

Triceps brachii: The triceps brachii are located in the arm and it straightens forearm at elbow.

External oblique: The external oblique is located in the abdomen and it compresses the abdomen; rotation of the trunk.

Latissimus dorsi: The latissimus dorsi is located in the back and it brings arm down and backward behind the body.

Gluteus maximus: The gluteus maximus is located on the butt and it extends thigh back.

Quadriceps femoris: The quadriceps femoris are located in the leg and they straighten the leg at the knee; raise the thigh.

Gastrocnemius: The gastrocnemius is located in the leg and it turns the foot downward, as when standing on toes and bends the leg at the knee.

4. Define myofibrils, sarcomeres, myosin, and actin - Myofibrils: Contractile portion of muscle cells that contains a linear arrangement of sarcomeres and shortens to produce muscle contraction. - Sarcomeres: One of many units, arranged linearly within a myofibril, whose contraction produces muscle contraction. - Myosin: One of two major proteins of muscle; makes up thick filaments in myofibrils of muscle fibers.

5. Describe the structure of a sarcomere's thick and thin filaments. - Thick filaments: A thick filament is composed of several hundred molecules of the protein myosin. Each myosin molecule is shaped like a gold club, with the straight portion of the molecule ending in a globular head, or cross bride. The cross bridges occur on each side of a sarcomere but not in the middle. - Think filaments: Primarily, a think filament consists of the 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?) - Sliding filament model: An explanation for muscle contraction based on the movement of actin filaments in relation to myosin filaments.