sliding filament theory

Folie 1

• The Sliding Filament Theory
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Folie 2

• It all begins with the Myofibril
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Folie 3

• Within the myofibril, there are sarcomeres. The sarcomeres are units that contract.
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• Bildunterschrift: There are many sarcomeres with the length of the myofibril

Folie 4

• The thick and thin protein filaments are what caused the striated appearance of the skeletal muscle.
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• Bildunterschrift: When the filaments slide past each other the muscle is contracting.

Folie 5

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• Bildunterschrift: The thick filaments are myosin
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• Bildunterschrift: The thin filaments are actin

Folie 6

• Even though the action between the filaments is referred to as "sliding", the myosin filament is actually pulling the actin filament.
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Folie 7

• The pulling/sliding of the filaments happens when the crossbridges of the myosin filaments attach to the actin filaments.
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Folie 8

• The muscle contraction begins when the ATP is broken down.
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• Bildunterschrift: The ATP is broken down when the myosin head reacts with Potassium

Folie 9

• While a lot of things have happened, they are all controlled by the actions of calcium.
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Folie 10

• Before you can understand calcium's role in muscle contraction, you have to understand the way actin filaments are structured.
• Actin filaments have the proteins troponin and tropomyosin.
• When the muscle is relaxed the tropomyosin blocks the binding sites on the actin. This prevents a crossbridge.
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Folie 11

• But, when the calcium levels are high enough and ATP is present, calcium ions bind to the troponin. This causes the tropomyosin to move.
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• Bildunterschrift: Here you can see the calcium ions binded to the tropomin

Folie 12

• When the tropomyosin moved, the binding site on the actin was exposed. This enabled myosin to attatch to the actin, and form a crossbridge.
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Folie 13

• This is why calcium ions flow to the myofibrils and how they initiate muscle contraction.
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Folie 14

• When the actin and myosin slide along each other the entire sacromere shortens.
• When the sacromere and myofibrils contract the entire muscle shortens.
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