Nerve activates contraction - Woodland Hills School District

Nerve activates contraction - Woodland Hills School District

6 The Muscular System PART B PowerPoint Lecture Slide Presentation by Jerry L. Cook, Sam Houston University ESSENTIALS OF HUMAN ANATOMY & PHYSIOLOGY EIGHTH EDITION

ELAINE N. MARIEB Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Sliding Filament Theory Figure 6.8 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Contraction of a Skeletal Muscle 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 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Types of Graded Responses Twitch Single, brief contraction Not a normal muscle function

Figure 6.9ab Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Types of Graded Responses 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 6.9ab Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Types of Graded Responses Unfused (incomplete) tetanus Some relaxation occurs between contractions The results are summed Figure 6.9cd

Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Types of Graded Responses Fused (complete) tetanus No evidence of relaxation before the following contractions The result is a sustained muscle contraction Figure 6.9cd Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Muscle Response to Strong Stimuli 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 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction 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 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction 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 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Energy for Muscle Contraction 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 6.10b Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction 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 6.10c Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction Anaerobic glycolysis (continued) This reaction is not as efficient, but is fast Huge amounts of glucose are needed Lactic acid produces

muscle fatigue Figure 6.10c Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Fatigue and Oxygen Debt 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 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Types of Muscle Contractions 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 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Tone 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

Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscles and Body Movements Movement is attained due to a muscle moving an attached bone Figure 6.12 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Muscles and Body Movements Muscles are attached to bone (or other connective tissue structures) by at least two points Origin the stationary, immoveable, or less movable attachment Insertion the movable attachment

Figure 6.12 Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings Effects of Exercise on Muscle Results of increased muscle use Increase in muscle size Increase in muscle strength Increase in muscle efficiency Muscle becomes more fatigue resistant Copyright 2006 Pearson Education, Inc., publishing as Benjamin Cummings

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