Skeletal Muscles- Contraction

1. Skeletal Muscles- Contraction Prof. K. Sivapalan

2. Actin Filament • It is made up of actin, tropomyosin and troponin. • Troponin I is bound to actin and tropomyosin and covers the myosin binding site • Ca++ binds to Troponin C • This causes exposure of Myosin binding site. Skeletal Muscle Contraction

3. Skeletal Muscle Contraction

4. Myosin Filament • Myosin has a head and a tail • Each filament may have 200 or more myosin molicules • The tails are bundled as the body while the heads hang outwards on a small arm – cross bridge • The head has ATPase activity • The cross bridge is flexible at hinges Skeletal Muscle Contraction

5. Contraction Skeletal Muscle Contraction

6. Sliding of Actin on Myosin • At rest ATP binds to the head of the myosin, converted to ADP, the energy stored in the head. • At this state, the head is perpendicular to the filament. • When binding site of the actin is exposed, actin – myosin binding occurs. • This binding changes the conformation of the cross bridge and causes ‘power stroke’ with energy stored as a ‘cocked spring’ • the stroke results in detachment of the cross bridge, release of ADP and attachment of another ATP Skeletal Muscle Contraction

7. Muscle Twitch- Experimental Design Skeletal Muscle Contraction

8. Muscle Twitch • When one single stimulus is given, the muscle contracts and relaxes after a latency • The latency is the time taken for excitation- contraction coupling Skeletal Muscle Contraction

9. Staircase Phenomenon Skeletal Muscle Contraction

10. Summation Skeletal Muscle Contraction

11. Tetanization Skeletal Muscle Contraction

12. Length – Strength • The force developed by the muscle depends on the length of the muscle. • It increases to maximum and then decreases. Skeletal Muscle Contraction

13. Actin-Myosin Overlap and Tension Developed • When muscle shortened, action myosin linkages are less. • When the length increases, more and more linkages become possible • When over stretched, again linkages are less Skeletal Muscle Contraction

14. Motor Units and Strength • Muscle fibers innervated by one axon constitute one motor unit. • The size of the motor unit is the number of muscle fibers in it. • The tension developed will depend on the number of myofibriles in each fiber and the size of the motor unit. Skeletal Muscle Contraction

15. Fast and Slow Fibers • Muscle fibers vary in myosin ATPase activity, contractile speed and other properties • The muscles can contain a mixture of three fiber types: • type I (or SO for slow-oxidative); • type IIA (FOG for fast-oxidative-glycolytic) • type IIB (FG for fast glycolytic). Skeletal Muscle Contraction

16. Muscle Type and Response Skeletal Muscle Contraction

17. Fiber Types Skeletal Muscle Contraction

18. Metabolism in Muscle • Glucose and free fatty acids • Oxygen debt mechanism • Importance of glycogen and myoglobin • Depends on the muscle type • Genetic suitability to type of sports • Alcohol and muscle performance Skeletal Muscle Contraction

19. Electromyography- EMG Skeletal Muscle Contraction

20. Skeletal Muscle Contraction

21. Effects of Denervation • Atrophy – less myofibrils • Fibrillations- receptor hypersensitivity • Fasciculation – motor unit function Skeletal Muscle Contraction