1. Skeletal muscle contraction
Contraction, force and tension
Sliding Filament Theory of Contraction
Contraction cycle
Regulation of the contraction cycle

2. Muscle contraction Movement or resist a load (force)
Load is the weight or force that opposes the contraction of a muscle
Tension is the force created by a muscle
Need ATP to generate tension

3. Observations during muscle contraction
Muscle shortens when
it moves a load.
(When muscle contracts, it does not always shorten)

4. Observations during muscle contraction:
A band does not shorten during contraction.

5. How about force without movement?
Sliding filament theory of contraction: movement and force
Resting length
How about force without movement?

6. During contraction Z discs move closer together Sarcomere shortens
A band same length
I band reduced
H band reduced

7. What pushes the actin filaments into the myosin?
Cross-bridges link myosin to actin
Power stroke: myosin head binds to actin  myosin head release actin. Repeated many times.
Myosin molecules are flexible
ATP causes movement of myosin molecules

8. Myosin
A motor protein
Converts chemical bond energy of ATP to mechanical energy of motion
Each myosin as ATPase
Energy from ATP hydrolysis is stored as potential energy in the myosin molecule, and is used to create the power stroke.

10. Why don’t actin and myosin continuously bind together?
ATP is usually available
Actin’s binding site for myosin is revealed only during cross-bridge (binding).
During relaxation, actin’s binding site for myosin is concealed