1. The Muscular System 1

2. Muscles are responsible for all types of body movement
Three basic muscle types are found in the body

3. Characteristics of Muscles
Muscle cells are elongated (all muscle cells are called muscle fibers)
All muscles share some terminology
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh

4. Skeletal Muscle Characteristics
Cells are multinucleate
Striated – have visible banding
Cells are surrounded and bundled by connective tissue

6. Connective Tissue Wrappings of Skeletal Muscle
Endomysium – around single muscle fiber
Perimysium – around a fascicle (bundle) of fibers
Fascia – on the outside of the epimysium

7. Skeletal Muscle Attachments
Epimysium blends into a connective tissue attachment
Tendon – cord-like structure
Aponeuroses – sheet-like structure
Sites of muscle attachment

8. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Found mainly in the walls of hollow organs

9. Cardiac Muscle Characteristics
Has striations
Usually has a single nucleus
Joined to another muscle cell at an intercalated disc

10. Function of Muscles

11. Microscopic Anatomy of Skeletal Muscle
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum
Figure 6.3a

12. Myofibril Microscopic Anatomy of Skeletal Muscle
Bundles of myofilaments
Myofibrils are aligned to give distrinct bands
Figure 6.3b

13. Microscopic Anatomy of Skeletal Muscle
Sarcomere

14. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thick filaments = myosin filaments

15. Organization of the sarcomere
Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere

16. Myosin and actin overlap somewhat
Microscopic Anatomy of Skeletal Muscle
Myosin and actin overlap somewhat

17. Sarcoplasmic reticulum (SR) – for storage of calcium
Microscopic Anatomy of Skeletal Muscle
Sarcoplasmic reticulum (SR) – for storage of calcium
Figure 6.3d

18. Nerve Stimulus to Muscles
Skeletal muscles must be stimulated by a nerve to contract
Motor unit

19. Motor units
Definition: A motor neuron and all the muscle fibers it contacts
Motor neuron activation causes contraction of all associated muscle fibers

21. Nerve Stimulus to Muscles
Neuromuscular junctions

22. Nerve Stimulus to Muscles
Synaptic cleft –
Nerve and muscle do not make contact
Area between nerve and muscle is filled with interstitial fluid
Figure 6.5b

23. 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+)

24. Transmission of Nerve Impulse to Muscle
Sodium rushing into the cell generates an action potential

25. Myosin heads then bind to the next site of the thin filament
The Sliding Filament Theory of Muscle Contraction
Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament
Myosin heads then bind to the next site of the thin filament

26. This continued action causes a sliding of the myosin along the actin
The Sliding Filament Theory of Muscle Contraction
This continued action causes a sliding of the myosin along the actin
Figure 6.7
Slide 6.17b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

27. The Sliding Filament Theory

28. 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

29. Muscle Response to Strong Stimuli
More fibers contracting results in greater muscle tension
Muscles can continue to contract unless they run out of energy