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

Contraction of a Skeletal Muscle Slide 6.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Muscle fiber contraction is “all or none”  Within a skeletal muscle, not all fibers may be stimulated during the same interval  Different combinations of muscle fiber contractions may give differing responses  Graded responses – different degrees of skeletal muscle shortening

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 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Initially, muscles use 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

Energy for Muscle Contraction Slide 6.24 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Direct phosphorylation  Muscle cells contain creatine phosphate (CP)  CP is a high-energy molecule  After ATP is depleted, ADP is left  CP transfers energy to ADP, to regenerate ATP  CP supplies are exhausted in about 20 seconds Figure 6.10a

Energy for Muscle Contraction Slide 6.25 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Aerobic Respiration  Series of metabolic pathways that occur in the mitochondria  Glucose is broken down to carbon dioxide and water, releasing energy  This is a slower reaction that requires continuous oxygen Figure 6.10c

Energy for Muscle Contraction Slide 6.26a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Anaerobic glycolysis  Reaction that breaks down glucose without oxygen  Glucose is broken down to pyruvic acid to produce some ATP  Pyruvic acid is converted to lactic acid Figure 6.10b

Energy for Muscle Contraction Slide 6.26b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Anaerobic glycolysis (continued)  This reaction is not as efficient, but is fast  Huge amounts of glucose are needed  Lactic acid produces muscle fatigue Figure 6.10b

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

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 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

Muscles and Body Movements Slide 6.30a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Movement is attained due to a muscle moving an attached bone Figure 6.12

Muscles and Body Movements Slide 6.30b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Muscles are attached to at least two points  Origin – attachment to an immoveable bone  Insertion – attachment to a movable bone Figure 6.12

Skeletal Muscle Actions prime mover (agonist) – primarily responsible for movement synergists – assist prime mover antagonist – resist prime mover’s action and cause movement in the opposite direction

Body Movement Four Basic Components of Lever 1. rigid bar – bones 2. fulcrum – point on which bar moves; joint 3. object - moved against resistance; weight 4. force – supplies energy for movement; muscles

Levers and Movement

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  Increase in muscle strength  Increase in muscle efficiency  Muscle becomes more fatigue resistant

Types of Contractions isotonic – muscle contracts and changes length concentric – shortening contraction eccentric – lengthening contraction isometric – muscle contracts but does not change length

Fast and Slow Twitch Muscle Fibers Slow-twitch fibers (type I) always oxidative resistant to fatigue red fibers most myoglobin good blood supply Fast-twitch glycolytic fibers (type IIa) white fibers (less myoglobin) poorer blood supply susceptible to fatigue Fast-twitch fatigue- resistant fibers (type IIb) intermediate fibers oxidative intermediate amount of myoglobin pink to red in color resistant to fatigue

Life-Span Changes myoglobin, ATP, and creatine phosphate decline by age 80, half of muscle mass has atrophied adipose cells and connective tissues replace muscle tissue exercise helps to maintain muscle mass and function

Clinical Application Myasthenia Gravis autoimmune disorder receptors for ACh on muscle cells are attacked weak and easily fatigued muscles result difficulty swallowing and chewing ventilator needed if respiratory muscles are affected treatments include drugs that boost ACh removing thymus gland immunosuppressant drugs antibodies