Thin Filaments - Skeletal muscle(and cardiac muscle are...

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Thin Filaments Actin forms the thin filaments of myofilaments. Actin filaments are two strands of the filamentous form of actin twined around each other. This creates a groove that binds to tropomyosin proteins. When bound to actin, tropomyosin blocks the active sites on actin, thus preventing the myosin heads from binding to actin. Tropomyosin is bound to a troponin protein. In response to stimulation, calcium enters the sarcoplasm of the myofiber and binds to troponin. This action causes tropomyosin and troponin to move off of the actin strand and enables the myosin heads to bind to actin. Striations
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Unformatted text preview: Skeletal muscle (and cardiac muscle) are called striated because when viewed in a microscope, there is a distinct pattern of light and dark bands. The dark bands are called A Bands while the light colored bands are I Bands. The A Band is a region where the thick and thin filaments overlap. Within the A Band, there is a lighter, central H Band that contains no thin filaments but only thick filaments (and mostly only myosin tails). The I Band is a region that contains only thin filament proteins and is bisected by a Z Disc. A sarcomere extends from one Z Disc to another....
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