1. Muscle Physiology
Chapter 1

2. Objectives Describe the micro and macrostructure of muscle
Describe the sliding filament theory
Differentiate types of muscle actions
Discuss factors that affect force production

3. Huxley?

4. KEY POINT
The muscular system is the organ system responsible for movement. Muscles develop tension, causing bones to act as levers and rotate around an axis.

6. Neuromuscular Components
Neuromuscular junction- the point where a motor neuron joins muscle fibers, the motor end plate
Motor unit- a motor neuron and all the muscle fibers it innervates
All or none law- all the muscle fibers in a motor unit contract, or none contract

10. Structure of a Muscle Cell
Sarcoplasm- the cytoplasm of a muscle fiber, contains mitochondria, sarcoplasmic reticulum
Sarcomere- smallest contractile unit of muscle tissue
Sarcoplasmic Reticulum – contains calcium.

16. Structure of a Muscle Cell
Myofibrils- long fibers in the sarcoplasm of muscle cells
Actin (thin)
Myosin (thick)
Crossbridges- globular heads on the myosin molecules

18. Structure of Skeletal Muscle
Contractile proteins- actin and myosin
Myofibril- muscle fiber, one muscle cell
Regulatory proteins- troponin and tropomyosin
Sarcomere- Z-line to Z-line
Sarcoplasmic reticulum/T-tubules- “communications” system in the muscle cell

20. Sliding Filament Theory of Muscle Contraction
1. Resting phase- calcium is segregated in the sarcoplasmic reticulum (SR), few crossbridges are attached, the muscle cell is “at rest”

21. Sliding Filament Theory of Muscle Contraction
2. Excitation phase- contraction coupling phase- calcium ions are released from the SR, troponin and tropomyosin undergo a conformational change, allowing actin to bind to myosin, causing flexion of the myosin head

22. Sliding Filament Theory of Muscle Contraction
3. Contraction phase- ATP causes myosin heads to detach from actin, ATP is hydrolized which “cocks” the myosin head, the myosin head attaches to the next active site

23. Sliding Filament Theory of Muscle Contraction
4. Recharge phase- as long as ATP is present to break the attraction of actin to myosin, and calcium is present, the cycle continues causing tension to develop in the muscle

24. Sliding Filament Theory of Muscle Contraction
5. Relaxation phase- stimulation from the motor nerve stops, calcium is re-segregated into the sarcoplasmic reticulum, troponin and tropomyosin return to their original shape and block the attraction of actin and myosin, the muscle returns to the resting unbound state

25. Cycle Time

26. Sliding Filament Animation

31. Summary of Muscle Contraction
Acetylcholine (ACH) released from terminal portion of motor neuron
ACH crosses the gap at the neuromuscular junction
Muscle fiber membrane depolarizes through transverse tubules to the sarcoplasmic reticulum

32. Next Class
Finish Chapter 1