Skeletal muscle contraction

1. Skeletal Muscle Contraction

2. Structure of each muscle fibre and organisation

3. SARCOTUBULAR SYSTEM

4. Structure and Arrangement of Myosin Molecules
Within Thick Filament

5. STRUCTURE OF SARCOMERE

6. STRUCTURE OF THICK AND THIN FILAMENTS

7. Banding pattern of skeletal muscle under
microscope

9. Changes in Banding Pattern During Shortening

10. Excitation contraction coupling
T Tubules and Sarcoplasmic Reticulum

12. MOLECULAR BASIS OF SKELETAL MUSCLE
CONTRACTION
1. Excitation – Contraction Coupling
2. Actin – Myosin Interaction-Cross Bridge Formation
& Cross – Bridge Cycling – Sarcomere Shortening
3. Relaxation

13. Excitation Contraction Coupling
• The process by which depolarization of a muscle
fibre initiates contraction is called excitation-
contraction coupling.
• There has to be cross bridge activity in the muscle
fibre following AP in the plasma membrane of
muscle fibre.

14. Skeletal Muscle Contraction: EXCITATION CONTRACTION
COUPLING
Figure 12-11a: Excitation-contraction coupling

15. Figure 12-11b: Excitation-contraction coupling

16. Role of Calcium in Cross-Bridge
Formation
• During relaxed state

17. Role of Calcium in Cross-Bridge
Formation
• Excited

18. Sliding Filament Mechanism
• Cross-bridge interaction between actin and myosin brings
about muscle contraction by means of the sliding filament
mechanism.
• Increase in Ca2+ starts filament sliding
• Decrease in Ca2+ turns off sliding process
• Thin filaments on each side of sarcomere slide inward over
stationary thick filaments toward center of A band during
contraction
• As thin filaments slide inward, they pull Z lines closer
together
• Sarcomere shortens
• All sarcomeres throughout muscle fiber’s length shorten
simultaneously
• Contraction is accomplished by thin filaments from opposite
sides of each sarcomere sliding closer together between thick
filaments.

19. Changes in Banding Pattern During Shortening

20. Power Stroke
• Activated cross bridge bends toward center of thick
filament, “rowing” in thin filament to which it is
attached
– Sarcoplasmic reticulum releases Ca2+
– Myosin heads bind to actin
– Hydrolysis of ATP transfers energy to myosin head and
reorients it
– Myosin heads swivel toward center of sarcomere (power
stroke)
– ATP binds to myosin head and detaches it from actin

23. CROSS-BRIDGE CYCLE

24. &2
SKELETAL MUSCLE CONTRACTION

25. SKELETAL MUSCLE CONTRACTION

26. SKELETAL MUSCLE CONTRACTION

27. Cross Bridge Formation

29. RELAXATION OF SKELETAL
MUSCLES

30. ROLE OF ATP
3 ROLES
1. Provides the energy of the power stroke
2. Causes detachment of myosin head from actin.
3. Causes relaxation of muscle by supplying the
energy for pumping back calcium into the
terminal cistern

31. Difference between cardiac muscle and
skeletal muscle contraction
Cardiac muscle
• Single nucleus
• Gap junction-syncitium
• Diameter of cell-greater
• T tubules-large and lie at
the level of Z line
• Release of Ca - Ca
dependent Ca release
Skeletal muscle
• Multinucleated
• No such
• Lesser
• T-tubule s lie at the
junction of A-I
• Release of Ca-
mechanical interaction
between DHPR & RYR