01 force-length relation

Musclestructure

• muscle fascicle

• Muscle fiber

• Myofibril

• Sarcomere (Myosin, actin, titin, z-line)

• Cross bridge

ATP cross bridge cycle

1. Rigor state: Myosin head is strongly bound to actin; no ATP attached

2. ATP binding: ATP binds to myosin → myosin detaches from actin

3. ATP hydrolysis: ATP→ ADP + Pi , energy re-cocks the myosin head

4. Power stroke: Pi is released → myosin pulls actin; force is generated

5. ADP release: ADP leaves → myosin returns to the rigor state

6. Cycle repeats: A new ATP molecule binds and the cycle starts again

How does myosin move along actin

Through discrete, stepwise movements

How large is one myosin step

11nm

How much force does one myosin molecule generate

3-4pN per force transient

How many myosin molecules work at 300N

10^14 myosin molecules simultaneously

Force-length relationship

Relationship between muscle eight and the force it produces

Sarcomere structure

Force-length description

The active force generated by a sarcomere is a function of its length.

Force varies as the thick and thin filaments slide past each other. Force increases with length in the ascending limb of the curve, plateaus, and decreases with length in the descending limb. Force generation peaks when the maximum number of cross-bridges are formed. Adapted from Gordon et al. (1966).

What is the passive component of muscle force

Force produced when muscle is stretched without active contraction