Microanatomy of Muscles Ch. 6b

Microscopic Anatomy of Skeletal Muscle Slide 6.9a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Muscle Fibers are composed of bundles of myofibrils Figure 6.3a

Microscopic Anatomy of Skeletal Muscle Slide 6.10a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Myofibril  Made of bundles of myofilaments  Myofibrils are aligned to give distinct bands  I band = light band  A band = dark band Figure 6.3b

Quick Quiz A muscle fiber is made up of what?

Microscopic Anatomy of Skeletal Muscle Slide 6.10b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Sarcomere  Contractile unit of a muscle fiber  Makes muscles contract  Extends from the center of one I band to the center of the next I band Figure 6.3b

Microscopic Anatomy of Skeletal Muscle Slide 6.11a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Organization of the sarcomere  Thick filaments = myosin filaments  Thin filaments = actin filaments Figure 6.3c

Microscopic Anatomy of Skeletal Muscle Slide 6.12a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Myosin filaments have heads (extensions, or cross bridges)  Myosin and actin overlap somewhat Figure 6.3d

Quick Quiz 1 of 3 What are the names of the microfilaments responsible for muscle contraction?

Properties of Skeletal Muscle Activity Slide 6.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Irritability – ability to receive and respond to a stimulus  Contractility – ability to shorten when an adequate stimulus is received

Nerve Stimulus to Muscles Slide 6.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Skeletal muscles must be stimulated by a nerve to contract Figure 6.4a

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

Sliding Filament Animation

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 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

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

Quick Quiz 2 of 3 Stored _____ is used for initial energy in muscles, but only lasts a few seconds. Aerobic respiration provides ATP, but only in the presence of __________ ________ acid is a result of anaerobic glycolysis.

Muscle Fatigue Slide 6.27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  When a muscle is fatigued, it is unable to contract  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  Ex: Lifting a book  Isometric contractions  Tension in the muscles increases  The muscle is unable to shorten  Ex: Trying to lift a car

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

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

Quick Quiz 3 of 3 Why type of muscle contraction is at work when doing a wall sit? Give an example of an isotonic muscle contraction.

Assignment Draw, color, label a muscle & Myofibril