Essentials of Human Anatomy & Physiology Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slides 6.18 – 6.31 Seventh Edition Elaine N. Marieb Chapter 6 The Muscular System Lecture Slides in PowerPoint by Jerry L. Cook

Contraction of a Skeletal Muscle Slide 6.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Graded response – different degrees of skeletal muscle shortening due to d ifferent combinations of muscle fiber contractions. Muscle fiber contraction is “all or none” BUT Not all fibers in a muscle are stimulated at same time

Types of Graded Responses Slide 6.20a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Twitch  Single, brief contraction  Not a normal muscle function Figure 6.9a, b

Types of Graded Responses Slide 6.20b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Tetanus (summing of contractions)  One contraction is immediately followed by another  The muscle does not completely return to a resting state  The effects are added Figure 6.9a, b

Types of Graded Responses Slide 6.21a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Unfused (incomplete) tetanus  Some relaxation occurs between contractions  The results are summed Figure 6.9a, b Figure 6.9c,d

Types of Graded Responses Slide 6.21b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Fused (complete) tetanus  No evidence of relaxation before the following contractions  The result is a sustained muscle contraction Figure 6.9a, b Figure 6.9c,d

Muscle Tone Slide 6.29 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Some fibers are contracted even in a relaxed muscle  Different fibers contract at different times to provide muscle tone  The process of stimulating various fibers is under involuntary control

Types of Muscle Contractions Slide 6.28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Isotonic contractions  Myofilaments are able to slide past each other during contractions  The muscle shortens  Isometric contractions  Tension in the muscles increases  The muscle is unable to shorten

Muscle Response to Strong Stimuli Slide 6.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Muscle force depends upon the number of fibers stimulated  More fibers contracting results in greater muscle tension  Muscles can continue to contract unless they run out of energy

Energy for Muscle Contraction Slide 6.23  Initially, muscles used stored ATP for energy  Bonds of ATP are broken to release energy  Only 4-6 seconds worth of ATP is stored by muscles  After this initial time, other pathways must be utilized to produce ATP

Direct phosphorylation Muscle cells contain creatine phosphate Aerobic Respiration Anaerobic glycolysis produces muscle fatigue Huge amnts needed

Muscle Fatigue and Oxygen Debt Slide 6.27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  When a muscle is fatigued, it is unable to contract  The common reason for muscle fatigue is oxygen debt  Oxygen must be “repaid” to tissue to remove oxygen debt  Oxygen is required to get rid of accumulated lactic acid  Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

Effects of Exercise on Muscle Slide 6.31 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Results of increased muscle use  Increase in muscle size (added myofilaments)  Increase in muscle strength  Increase in muscle efficiency  Muscle becomes more fatigue resistant

The Sliding Filament Theory Slide 6.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.8