1. Essentials of Anatomy and Physiology
Fifth edition
Seeley, Stephens and Tate
Chapter 7: Muscular System
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Slide 2.1
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2. The Muscular System Muscles are responsible for body movement
Three types are found in the body
Skeletal muscle**
Cardiac muscle
Smooth muscle
Slide 6.1
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3. Types of Muscle
Skeletal
Cardiac
Smooth
Three types of muscle

4. Functions of Skeletal Muscles
Make up “flesh” of the body
Maintain Posture
Voluntary movement
Aid in breathing, eating, speech
Provide facial expression
Generate reflexes
Produce body heat
Slide 6.1
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5. Characteristics of Skeletal Muscles
Muscle cells are elongated (muscle cell = muscle fiber)
Muscles are specialized to contract
Terminology:
Prefix myo, mys refer to muscle
Prefix sarco refers to flesh
Slide 6.2
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6. Characteristics of Skeletal Muscles
Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Muscles and their fibers are wrapped by connective tissue
Slide 6.3
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7. Connective Tissue Wrappings of Skeletal Muscle
Endomysium – around single muscle fiber
Perimysium – around a fascicle (bundle) of fibers
Figure 6.1
Slide 6.4a
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8. Connective Tissue Wrappings of Skeletal Muscle
Epimysium – covers the entire skeletal muscle
Fascia – on the outside of the epimysium
Figure 6.1
Slide 6.4b
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9. Skeletal Muscle Attachments
Epimysium blends into a connective tissue attachment
Tendon – cord-like structure
Aponeurosis – sheet-like structure
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10. Skeletal Muscle Attachments
Sites of muscle attachment
Bones
Cartilages
C. T. coverings
i.e., aponeuroses
Slide 6.5
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11. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are deep to the sarcolemma
Figure 6.3a
Slide 6.9a
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12. Microscopic Anatomy Sarcolemma – specialized plasma membrane
Sarcoplasmic reticulum – specialized smooth E.R.
Stores Ca++
Required for contraction
Figure 6.3a
Slide 6.9b
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13. Microscopic Anatomy Myofibril: organelle unique to muscle
Bundles of myofilaments
Myofibrils alignment produces distinct bands
I band = light band
A band = dark band
Slide 6.10a
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14. Microscopic Anatomy
Banding Pattern depends on arrangement of proteins in myofibrils
Actin: thin
A and I bands
Myosin: thick
A bands
I-band
A-band
Figure 6.3b
Slide 6.10a
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15. Microscopic Anatomy Sarcomere Contractile subunit of a muscle fiber
From “Z to Z”
One A band +
Two “half” I bands
Figure 6.3b
Slide 6.10b
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16. Microscopic Anatomy Organization of the sarcomere
Thick filaments = myosin filaments
Composed of the protein myosin
Has ATP-ase enzymes
Figure 6.3c
Slide 6.11a
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17. Microscopic Anatomy Organization of the sarcomere, con’t…
Thin filaments = actin filaments
Composed of the protein actin
Figure 6.3c
Slide 6.11b
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18. Microscopic Anatomy
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap
Figure 6.3d
Slide 6.12a
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19. Microscopic Anatomy
At rest, there is a bare [“H”] zone that lacks actin filaments
Figure 6.3d
Slide 6.12b
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20. Properties of Skeletal Muscle
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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21. Nerve Stimulus to Muscles
Skeletal muscles require innervation
Motor unit
One motor neuron +
Muscle cells innervated by that neuron
Figure 6.4a
Slide 6.14
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22. Neuromuscular Junction
Nerve Stimulus to Muscles
Neuromuscular junction:
communication site between a motor neuron and a muscle fiber
Motor Neuron
Neuromuscular Junction
Figure 6.5b
Slide 6.15a
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23. Nerve Stimulus to Muscles
Synaptic cleft : gap between nerve and muscle
Nerve and muscle do not make direct contact
Figure 6.5b
Slide 6.15b
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24. Transmission of Nerve Impulse to Muscle
Neurotransmitter – chemical released by motor nerve
initiates contraction
Causes sarcolemma to depolarize
For skeletal muscle: acetylcholine (Ach)
Slide 6.16a
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25. Transmission of Nerve Impulse to Muscle
Slide 6.16a
Action of Neurotransmitter
Crosses synaptic cleft
Attaches to receptors on the sarcolemma
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26. Muscle Contraction An electrochemical event
Ach is the chemical
Before contraction can occur, sarcolemma must be polarized
A polarized membrane is more “+” outside and more “-” inside
Movement of ions creates “action potential”
The ability to do work
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27. Muscle Contraction Ach attaches to receptor sites
Sarcolemma becomes permeable to sodium (Na+)
Sodium rushes into the cell
Initiates “sliding filament” process
Slide 6.16b
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28. Muscle Contraction Membrane of sarcoplasmic reticulum also depolarizes
Ca++ ions are released
Bind to sites on actin
Open attachment sites for myosin
Slide 6.16b
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29. The Sliding Filament Theory of Muscle Contraction
Depolarization allows myosin heads to attach to binding sites on actin
called crossbridges
ATP required
Figure 6.7
Slide 6.17a
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30. The Sliding Filament Theory of Muscle Contraction
Actin is pulled past myosin by movement of heads
ATP required
Myosin heads detach
Then bind to the next site on actin
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31. The Sliding Filament Theory of Muscle Contraction
This continued action causes a sliding of the actin along the myosin
I band narrows
H zone narrows
A band stays the same
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32. The Sliding Filament Theory of Muscle Contraction
Actin slides past myosin
Results in shortening of the sarcomere
Muscle fiber has thousands of sarcomeres
All shorten at one time
Muscle contracts
Figure 6.7
Slide 6.17b
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