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
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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
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4. Role of Muscles in the Body
Produce movement
Maintain posture
Stabilize joints
Generate heat
Propel Substances
Slide 6.8
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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
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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
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9. Connective Tissue Wrappings of Skeletal Muscle
Fascicle - bundle of fibers
Epimysium – covers the entire skeletal muscle
Figure 6.1
Slide 6.4b
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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
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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
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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
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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
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17. Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum
Figure 6.3a
Slide 6.9b
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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
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19. Microscopic Anatomy of Skeletal Muscle
Sarcomere
Contractile unit of a muscle fiber
Figure 6.3b
Slide 6.10b
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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
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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
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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
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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
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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
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25. Nerve Stimulus to Muscles
Neuromuscular junctions – association site of nerve and muscle
Figure 6.5b
Slide 6.15a
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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
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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
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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
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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
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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
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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
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32. Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone
Figure 6.12
Slide 6.30a
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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
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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
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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
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36. Body Movements Slide 6.33 Figure 6.13
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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