Muscle contraction Flashcards
What are muscles made up
Bundles of muscle fibres packed together
What are myofibrils made up of
many sarcomeres which are made up of partly overlapping myosin and actin filaments
Which are thicker myosin or actin filament
myosin is thicker and actin is thinner
Explain the banding pattern seen under and electron microscope
I band = light bands that contain only thick actin filaments
A band = Dark bands that contain thick myosin filaments and some overlapping actin
What happens in muscle contraction
The myosin head slides along the myosin causing the sarcomere to contract
Simultaneous contraction of lots of sarcomeres causes myofibrils and muscle fibers to contract when sarcomeres shorten.
- H zones shorter
- I bands shorter
- A band same
- Z lines closer
Myofibril contraction Step 1 and 2
An action potential spreads down along the T tubule causing the release of calcium ions from the sarcoplasmic reticulum which diffuse into the sarcoplasm to the myofibril.
Calcium ions bind to the tropomyosin causing it to change shape exposing the myosin binding site to the actin.
Myofibril contraction step 3 and 4
Myosin heads with ADP attach to the binding sites and from an actin-myosin cross bridge.
Myosin head moves actin along myosin ( power stroke ATP required)
Myosin contraction step 5 and 6
ATP binds to the myosin head causing it to detach from the actin-binding site the cross-bridge is broken.
The Hydrolysis of ATP by ATPase releases energy for myosin heads to move back to the original position.
Myosin contraction step 7
Myosin reattaches to a different binding site further along the actin
Explain the properties of a slow twitch muscle fibre
- specialised for slow contractions
- maintain posture / long-distance running
- Located in muscles that give posture and long-distance runners.
- Aerobic respiration produces ATP to release energy slowly
- High levels of myoglobin ( red colour that stores ocygen
