1. Muscular System
Chp. 6

2. The Muscular System is very complex:
Figure 6.2

3. Muscle Function: Produce Movement or Generate Tension
Principle function - produce movement or generate tension
Contraction: shorten distances between bones
Skeletal muscles function to move bones
Two major types muscle groups:
Synergistic muscles: groups work together
Antagonistic muscles: groups oppose each other

4. Muscle Structure:
Fascicles = bundles of muscle cells surrounded by sheath (connective tissue)
Muscle fibers = few doz.- 1,000’s muscle cells
Connective tissue surrounding
entire muscle, collectively, these connective tissues form tendons.
Figure 6.3

5. Skeletal Muscle Contractile Unit:
Single muscle cell contains many myofibrils:
ea myofibril is composed of sacromeres
actin filaments
myosin filaments
z-lines

6. Skeletal Muscle Contractile Unit:
Sarcomere - segment of single myofibril from one Z-line to the next Z-line
Actin - protein w/tropomyosin binding sites
Myosin - thick filament w/ myosin heads
Z Lines - attachment points for sarcomeres
Actin filaments linked with z-line
Myosin filaments located w/in scaromeres

7. Skeletal Muscle Contractile Unit (cont.)
Figure 6.5

8. Nerve Activation of Individual Muscle Cells:
Acetylcholine released from motor neuron at neuromuscular junction
Electrical impulse transmitted along T tubules
Calcium released from sarcoplasmic reticulum

9. Nerve Activation of Individual Muscle Cells (cont.)
Figure 6.6

10. Calcium Initiates the Sliding Filament Mechanism
Thick filaments: myosin
Thin filaments: strands of actin molecules
Contraction = formation of cross bridges between thin & thick filaments

11. Calcium Initiates the Sliding Filament Mechanism (cont.)
Figure 6.7

12. Mechanism of Muscle Contraction:
Calcium released from sarcoplasmic reticulum
Calcium binds to troponin
Troponin-tropomysin complex shifts position
Myosin binding site exposed
Myosin heads form cross-bridges with actin
Actin filaments pulled toward center of sarcomere

13. Mechanism of Muscle Contraction (cont.)
Figure 6.8

14. Muscle Relaxation Nerve activation ends, contraction ends
Calcium pumped back into sarcoplasmic reticulum
Calcium removed from troponin
Myosin-binding site covered
No calcium = no cross-bridges

15. Energy Required for Muscle Activity
Principle source of energy: ATP
ATP replenished by variety of means
Creatine phosphate
Stored glycogen
Aerobic metabolism of glucose, fatty acids, and other high-energy molecules

16. Activity of Muscles Can Vary
Isotonic contractions: muscle shortens, movement occurs
Isometric contractions: muscle doesn’t shorten, no movement
Degree of nerve activation influences force
Terms to know:
Motor unit
Muscle tension
All-or-none principle
Muscle tone

17. Muscle Contraction: Myogram
Latent period
Contraction
Relaxation
Summation vs. tetanus
Figure 6.10

18. Slow Twitch vs. Fast Twitch Fibers
Muscle Activity:
Slow Twitch vs. Fast Twitch Fibers
Slow twitch muscles: endurance, long duration contraction, contains myoglobin
E.g. Jogging, swimming, biking
Fast twitch: strength, white muscle, short duration contraction
E.g. Sprinting, weight lifting, tennis

19. Exercise Training: Strength training Aerobic training
Resistance training
Short, intense
Builds more fast-twitch myofibrils
Aerobic training
Builds endurance
Increases blood supply to muscle cells
Target heart rate at least 20 minutes, three times a week

20. Features of Cardiac & Smooth Muscles:
Activation of cardiac and smooth muscles
Involuntary
Specialized adaptations in each
Speed and sustainability of contractions
3. Arrangement of myosin and actin filaments

21. Diseases and Disorders of the Muscular System
Muscular dystrophy
Tetanus
Muscle cramps
Pulled muscles
Fasciitis