1. Contraction II
Department of Biology, WCU

2. Revision
Sarcomere
bands and zones, filaments (thick, thin)

3. Myosin
1. tail and heads
2. cross bridge
3. head pivots

4. Actin
Actin
2 strands
Tropomyosin
stiffen actin
block myosin head

5. Actin Troponin: 3 polypeptides Functions
inhibit actin and myosin binding
rotates actin to enable myosin binding
binds to Ca++

6. Sliding filament theory
Sarcomeres shorten
Filament length does not shorten
Filaments slide

7. Sliding filament theory
1. Cross bridge attachment
Ca++ influx
tropomyosin release
myosin attachment
ATP conversion

8. Sliding filament theory
2. Power stroke
myosin head pivots
disappearance of H zone and I band
ADP + Pi release

9. Sliding filament theory
3. Cross bridge detachment
detachment
binding of new ATP
low to high energy confirmation

10. Sliding filament theory
Cross bridge reattachment
ATP hydrolysis
reattachment

11. Sliding filament theory
One power stroke results in 1% shortening
Muscles shorten by 30%
Many attachments and detachments

12. Rigor mortis What is stimulus for myosin detachment? ATP availability
Extracellular Ca++
Muscle stiffening
3 - 4 hr < 12 hr > hr