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6.3 Muscles - Coggle Diagram
6.3 Muscles
Sliding Filament Theory
Evidence: When a muscle is contracting
H-bands narrow
I-bands narrow
A-bands remain the same width
Z-lines get closer (sarcomere shortens)
Muscle Relaxation
Calcium ions are actively transported back into the sarcoplasmic reticulum
Tropomyosin moves back to block actin-binding sites on the actin filaments
An action potential arrives at the neuromusclar junction
Calcium ions are released from the SR
Calcium ions bind to tropomyosin, stimulating them to change shape
This causes troponin and tropomoyosin proteins to change position on the actin filaments
Myosin binding sites are exposed on the actin molecules
The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament
The formation of the cross-bridges causes the myosin heads to spontaneously bend (releasing ADP +Pi)
This pulls the actin filaments towards the centre of the sarcomere and causing the muscle to contract a very small distance
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