7 The Muscular System

Muscle Performance (7-7) Measured in force The maximum amount of tension produced by a muscle or muscle group Measured in endurance The amount of time a particular activity can be performed Two keys to performance Types of fibers in muscle Physical conditioning or training © 2013 Pearson Education, Inc.

Fast Fibers (7-7) The majority of muscle fibers in the body Large in diameter Large glycogen reserves Few mitochondria Rely on glycolysis Are rapidly fatigued © 2013 Pearson Education, Inc.

Slow Fibers (7-7) About half the diameter of, and three times slower than, fast fibers Are fatigue resistant because of three factors Oxygen supply is greater due to more perfusion Myoglobin stores oxygen in the fibers Oxygen use is efficient due to large numbers of mitochondria © 2013 Pearson Education, Inc.

Percentages of Muscle Types Vary (7-7) Fast fibers appear pale and are called white muscles Extensive vasculature and myoglobin in slow fibers cause them to appear reddish and are called red muscles Human muscles are a mixture of fiber types and appear pink © 2013 Pearson Education, Inc.

Muscle Conditioning and Performance (7-7) Physical conditioning and training Can increase power and endurance Anaerobic endurance Is increased by brief, intense workouts Hypertrophy of muscles results Aerobic endurance Is increased by sustained, low levels of activity © 2013 Pearson Education, Inc.

Cardiac Muscle Tissue (7-8) Found only in heart Cardiac muscle cells Relatively small with usually only one central nucleus Striated and branched Intercalated discs, which connect cells to other cells Communicate through gap junctions, allowing all the fibers to work together © 2013 Pearson Education, Inc.

Cardiac Pacemaker Cells (7-8) Exhibit automaticity Make up only 1 percent of myocardium Establish rate of contraction © 2013 Pearson Education, Inc.

Cardiac Contractile Cells (7-8) 99 percent of myocardium Contract for longer period than skeletal muscle fibers Unique sarcolemmas make tetanus impossible Are permeable to calcium Rely on aerobic metabolism © 2013 Pearson Education, Inc.

Smooth Muscle Tissue (7-8) Thick filaments are scattered throughout sarcoplasm Thin filaments are anchored to the sarcolemma Causing contraction to be like a twisting corkscrew Cells are bound together Resulting in forces being transmitted throughout the tissue © 2013 Pearson Education, Inc.

Smooth Muscle Tissue (7-8) Different from other muscle types Calcium ions from the extracellular fluid are needed to trigger a contraction mechanism that is different from other muscle tissues Function involuntarily Can respond to hormones or pacesetter cells © 2013 Pearson Education, Inc.

Figure 7-10 Cardiac and Smooth Muscle Tissues. muscle cell Intercalated discs Cardiac muscle tissue LM x 575 A light micrograph of cardiac muscle tissue. Circular muscle layer T Longitudinal muscle layer L Smooth muscle tissue LM x 100 Many visceral organs contain several layers of smooth muscle tissue oriented in different directions. Here, a single sectional view shows smooth muscle cells in both longitudinal (L) and transverse (T) sections. © 2013 Pearson Education, Inc.

Foldable: Muscle Types and Functions Skeletal Muscle Fiber size: Function: Nuclei: Control: Calcium Ion Source: Contraction Speed: Stamina: Energy Source: Cardiac Muscle Fiber size: Function: Nuclei: Control: Calcium Ion Source: Contraction Speed: Stamina: Energy Source: Smooth Muscle Fiber size: Function: Nuclei: Control: Calcium Ion Source: Contraction Speed: Stamina: Energy Source: © 2013 Pearson Education, Inc.

Smooth Muscle Tissue (7-8) Found in the walls of most organs, in the form of sheets, bundles, or sheaths Lacks myofibrils, sarcomeres, or striations Smooth muscle cells Also smaller than skeletal fibers Spindle-shaped and have a single nucleus © 2013 Pearson Education, Inc.

Table 7-2 A Comparison of Skeletal, Cardiac, and Smooth Muscle Tissues © 2013 Pearson Education, Inc.