Muscles & the Basis of Contraction in a Snap! Unlock the full A-level Biology course at [ Ссылка ] created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.
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The key points covered of this video include:
1. The Molecular Basis of Contraction
The Molecular Basis of Contraction
Sarcomeres contract when myosin interacts with actin to form a cross bridge - this happens in a sequence of steps: 1. An action potential travels into the muscle fibre via T tubules, which are in contact with the sarcoplasmic reticulum (muscle ER). 2. As the action potential reaches the sarcoplasmic reticulum, Ca2+ ion channels open and Ca2+ diffuses into the sarcoplasm. 3. The calcium ions released by the sarcoplasmic reticulum now bind to troponin. This causes the tropomyosin molecule to move, which exposes the myosin binding site on the actin filament. This allows myosin to attach to actin and form the actin-myosin cross-bridge. Once attached to actin, the myosin heads change shape, pulling the actin filaments along which releases a molecule of ADP. Then, a molecule of ATP attaches to the myosin head, causing it to change shape and detach from the actin filament. After this, ATPases are activated by the Ca2+ ions released by the sarcoplasmic reticulum. These ATPases breakdown the ATP attached to the myosin heads - this allows the myosin heads to return to its original position. The myosin heads are now detached and can attach to another binding site further down the actin filament and the process repeats. This process results in the actin filaments in one sarcomere being pulled in opposite directions, towards each other. As filaments slide past one another it causes the sarcomere to shorten - this process is known as Sliding Filament Model.
Summary
In order for muscles to contract, sarcomeres must shorten-this is known as the Sliding Filament Model
This process involves the transmission of an action potential deep into muscle fibre via T Tubules
This then causes a cascade of events that involve getting calcium ions to the tropomyosin and an actin myosin cross bridge forming
ATP and ADP play crucial roles in pulling the actin filament along and returning the shape of the myosin heads to normal respectively
This process then repeasts to facilitate sarcomere shortening and therefore muscle contraction
