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Chapter 6 The Muscular System

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1 Chapter 6 The Muscular System
Essentials of Human Anatomy & Physiology Seventh Edition Elaine N. Marieb Chapter 6 The Muscular System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

2 The Muscular System Skeletal muscle Cardiac muscle Smooth muscle
Essential function is contraction (shorten) Muscles are responsible for all types of body movement Three basic muscle types are found in the body Skeletal muscle Cardiac muscle Smooth muscle Slide 6.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

3 Characteristics of Muscles
Muscle cells are elongated (muscle cell = muscle fiber) Contraction of muscles is due to the movement of microfilaments All muscles share some terminology Prefix myo refers to muscle Prefix mys refers to muscle Prefix sarco refers to flesh Slide 6.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

4 Role of Muscles in the Body
Produce movement Maintain posture Stabilize joints Generate heat Propel Substances Slide 6.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

5 Skeletal muscle Functions Form smooth contours of body
Locomotion and breathing Maintain posture Heat production Form smooth contours of body Vary in shape (spindle, fan or circle shape)

6 Skeletal Muscle Characteristics
Striated – have visible banding Cells are multinucleate Voluntary – subject to conscious control Attached to bones Slow to fast contraction Slide 6.3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

7 Skeletal Muscle Activity
Contract rapidly but tire easily Can exert much power without ripping Cells are surrounded by connective tissue Adds strength and support

8 Connective Tissue Wrappings of Skeletal Muscle
Endomysium – around single muscle fiber Perimysium – surrounds multiple fibers Figure 6.1 Slide 6.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

9 Connective Tissue Wrappings of Skeletal Muscle
Fascicle - bundle of fibers Epimysium – covers the entire skeletal muscle Figure 6.1 Slide 6.4b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

10 Skeletal Muscle Attachments
Epimysium blends into a connective tissue attachment Tendon – cord-like structure Aponeuroses – sheet-like structure Sites of muscle attachment Bones Cartilages Connective tissue coverings Slide 6.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

11 Smooth muscle Lines walls of hollow organs Ex stomach, bladder
Found in two layers Layers alternately contract Function: Propels substances along a tract

12 Smooth Muscle Characteristics
No no striations Single nucleus Involuntary – no conscious control Found mainly in the walls of hollow organs Slow contraction Figure 6.2a Slide 6.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

13 Cardiac muscle Pumping mass of heart
Arranged in spiral or figure 8 shape Heart muscle cell behave as one unit Heart muscle always contracts to it’s full extent

14 Cardiac Muscle Characteristics
Striations Single nucleus Involuntary Found only in the heart Contracts at slow, steady rate Slide 6.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

15 Cardiac Muscle Activity
Intercalated disks closely coordinate activity Own pacemaker controls contraction Can be stimulated by the nervous system Muscle contracts  chambers become smaller forcing blood into arteries

16 Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate Nuclei are just beneath the sarcolemma Figure 6.3a Slide 6.9a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

17 Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum Figure 6.3a Slide 6.9b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

19 Microscopic Anatomy of Skeletal Muscle
Sarcomere Contractile unit of a muscle fiber Figure 6.3b Slide 6.10b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

20 Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere Thick filaments = myosin filaments Composed of the protein myosin Has ATPase enzymes Figure 6.3c Slide 6.11a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

21 Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere Thin filaments = actin filaments Composed of the protein actin Figure 6.3c Slide 6.11b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

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

24 Nerve Stimulus to Muscles
Skeletal muscles must be stimulated by a nerve to contract (motor neruron) Motor unit One neuron Muscle cells stimulated by that neuron Figure 6.4a Slide 6.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

25 Nerve Stimulus to Muscles
Neuromuscular junctions – association site of nerve and muscle Figure 6.5b Slide 6.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

26 Nerve Stimulus to Muscles
Synaptic cleft – gap between nerve and muscle Nerve and muscle do not make contact Area between nerve and muscle is filled with interstitial fluid Figure 6.5b Slide 6.15b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

27 Transmission of Nerve Impulse to Muscle
Neurotransmitter – chemical released by nerve upon arrival of nerve impulse The neurotransmitter for skeletal muscle is acetylcholine Neurotransmitter attaches to receptors on the sarcolemma Sarcolemma becomes permeable to sodium (Na+) Slide 6.16a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

28 Transmission of Nerve Impulse to Muscle
Sodium rushing into the cell generates an action potential Once started, muscle contraction cannot be stopped Slide 6.16b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

29 Contraction of a Skeletal Muscle
Muscle fiber contraction is “all or none” Not all fibers may be stimulated at the same time Slide 6.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

30 Contraction of a Skeletal Muscle
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 Slide 6.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

31 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 Slide 6.27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

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

34 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 Slide 6.31 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

35 Types of Ordinary Body Movements
Flexion – decreases angle of joint and brings two bones closer together Extension- opposite of flexion Rotation- movement of a bone in longitudinal axis, shaking head “no” Abduction/Adduction (see slides) Circumduction (see slides) Slide 6.32 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

36 Body Movements Slide 6.33 Figure 6.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

37 Left: Abduction – moving the leg away from the midline
Right: Circumduction: cone-shaped movement, proximal end doesn’t move, while distal end moves in a circle. Above – Adduction- moving toward the midline

38 Disorders relating to the Muscular System
Muscular Dystrophy: inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy Duchenne MD: lacking a protein to maintain the sarcolemma Myasthemia Gravis: progressive weakness due to a shortage of acetylcholine receptors


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