1. Skeletal Muscle Fibers
Skeletal Muscle Contraction
Sliding filament theory
Thin filaments of sarcomere slide toward M line, alongside thick filaments
The width of A zone stays the same
Z lines move closer together

2. Skeletal Muscle Fibers
Figure 10–8a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

3. Skeletal Muscle Fibers
Figure 10–8b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

4. Skeletal Muscle Fibers
Skeletal Muscle Contraction
The process of contraction
Neural stimulation of sarcolemma:
causes excitation–contraction coupling
Cisternae of SR release Ca2+:
which triggers interaction of thick and thin filaments
consuming ATP and producing tension

5. Skeletal Muscle Fibers
Figure 10–9 An Overview of Skeletal Muscle Contraction.

6. The Neuromuscular Junction
Is the location of neural stimulation
Action potential (electrical signal)
Travels along nerve axon
Ends at synaptic terminal
Synaptic terminal:
releases neurotransmitter (acetylcholine or ACh)
into the synaptic cleft (gap between synaptic terminal and motor end plate)

7. The Neuromuscular Junction
Figure 10–10a, b Skeletal Muscle Innervation.

8. The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.

9. The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.

10. The Neuromuscular Junction
The Neurotransmitter
Acetylcholine or ACh
Travels across the synaptic cleft
Binds to membrane receptors on sarcolemma (motor end plate)
Causes sodium–ion rush into sarcoplasm
Is quickly broken down by enzyme (acetylcholinesterase or AChE)

11. The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.

12. The Neuromuscular Junction
Action Potential
Generated by increase in sodium ions in sarcolemma
Travels along the T tubules
Leads to excitation–contraction coupling
Excitation–contraction coupling:
action potential reaches a triad:
releasing Ca2+
triggering contraction
requires myosin heads to be in “cocked” position:
loaded by ATP energy

13. The Neuromuscular Junction
Figure 10–11 The Exposure of Active Sites.

14. The Contraction Cycle Five Steps of the Contraction Cycle
Exposure of active sites
Formation of cross-bridges
Pivoting of myosin heads
Detachment of cross-bridges
Reactivation of myosin

15. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

16. The Contraction Cycle [INSERT FIG. 10.12, step 1]
Figure 10–12 The Contraction Cycle.

17. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

18. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

19. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

20. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

21. The Contraction Cycle Fiber Shortening Contraction Duration
As sarcomeres shorten, muscle pulls together, producing tension
Contraction Duration
Depends on
Duration of neural stimulus
Number of free calcium ions in sarcoplasm
Availability of ATP

22. The Contraction Cycle
Figure 10–13 Shortening during a Contraction.

23. The Contraction Cycle Relaxation Rigor Mortis Ca2+ concentrations fall
Ca2+ detaches from troponin
Active sites are re-covered by tropomyosin
Sarcomeres remain contracted
Rigor Mortis
A fixed muscular contraction after death
Caused when
Ion pumps cease to function; ran out of ATP
Calcium builds up in the sarcoplasm

24. The Contraction Cycle
Skeletal muscle fibers shorten as thin filaments slide between thick filaments
Free Ca2+ in the sarcoplasm triggers contraction
SR releases Ca2+ when a motor neuron stimulates the muscle fiber
Contraction is an active process
Relaxation and return to resting length are passive

25. The Contraction Cycle

26. ATP and Muscle Contraction
Sustained muscle contraction uses a lot of ATP energy
Muscles store enough energy to start contraction
Muscle fibers must manufacture more ATP as needed

27. ATP and Muscle Contraction
ATP and CP Reserves
Adenosine triphosphate (ATP)
The active energy molecule
Creatine phosphate (CP)
The storage molecule for excess ATP energy in resting muscle
Energy recharges ADP to ATP
Using the enzyme creatine phosphokinase (CPK or CK)
When CP is used up, other mechanisms generate ATP

28. ATP and Muscle Contraction
ATP Generation
Cells produce ATP in two ways
Aerobic metabolism of fatty acids in the mitochondria
Anaerobic glycolysis in the cytoplasm

29. ATP and Muscle Contraction
ATP Generation
Aerobic metabolism
Is the primary energy source of resting muscles
Breaks down fatty acids
Produces 34 ATP molecules per glucose molecule
Anaerobic glycolysis
Is the primary energy source for peak muscular activity
Produces two ATP molecules per molecule of glucose
Breaks down glucose from glycogen stored in skeletal muscles

30. ATP and Muscle Contraction

31. ATP and Muscle Contraction
Energy Use and Muscle Activity
At peak exertion
Muscles lack oxygen to support mitochondria
Muscles rely on glycolysis for ATP
Pyruvic acid builds up, is converted to lactic acid

32. ATP and Muscle Contraction
Figure 10–20 Muscle Metabolism.

33. ATP and Muscle Contraction
Figure 10–20a Muscle Metabolism.

34. ATP and Muscle Contraction
Figure 10–20b Muscle Metabolism.

35. ATP and Muscle Contraction
Figure 10–20c Muscle Metabolism.