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Steps of muscle contraction - Liam Donnelly - Coggle Diagram
Steps of muscle contraction - Liam Donnelly
The first step to a muscle contracting is action potential arriving in a motor neuron and triggering the release of neurotransmitters.
The neurotransmitters diffuses across the synaptic cleft and binds to the sarcolemma.
The Ion exchange excites the muscle, sending a signal down T tubules to activate the contraction process.
The signal is sent to the sarcomere, which in response releases Calcium ions.
These calcium ions will then bind to the regulatory protein that prevents actin and myosin from reaching each other.
The regulatory proteins are Troponin and Tropomyosin. Tropomyosin blocks the active site on the actin while Troponin holds it to the area. When troponin moves, it also moves the tropomyosin.
The Calcium ions are able to temporarily remove the Tropomyosin from the active site by binding to Troponin. As stated above, Troponin hold Tropomyosin in place, but Troponin is a protein. Proteins have the ability to change shape whenever they bond with something, so when Calcium binds to Troponin it changes shape. The causes Troponin to relax the Tropomyosin, allowing a space on the active site for myosin to bond to.
Actin and myosin are two filaments of the sarcomere, and they allow the muscle to contact. They are attracted to each other in such a way that myosin is able to pull the actin towards a center area of the sarcomere called the M line. The only thing stopping this from forever happening non-stop is tropomyosin.
The muscle cell starts to contract.
Once Troponin has changed shape, and Tropomyosin has been moved off actin's active site, myosin head will cock back, push up to the active site, and push the actin forwards, before going back down and doing it again. This happens until the Calcium disconnects from Troponin and Tropomyosin blocks the active site once more.
The myosin gets the energy by turning ATP (adenine triphosphate) into ADP + P (adenine diphosphate plus a phosphate). This is an exergonic reaction, meaning it releases energy. This energy is taken up by the myosin heads and used to fuel to fuel most of the process. In order to push the actin forwards and relax, the myosin heads must release these components. They then perform an endergonic reaction (it takes in energy) outside of the myosin heads, and binds back into ATP. It is then taken back in by the myosin heads to repeat the process.
Acetylcholine specifically binds to transport proteins on the bumpy sarcolemma, and it opens them to allow an exchange of ions.
The ions exchanged create a positive charge by intaking more Na+ ions while releasing barely any K+ ions.
After this, an enzyme called acetylcholinesterase will break down the acetylcholine on the transport protein, stopping the increase of a positive charge.
It specifically arrives in the axon terminal. It triggers Calcium 2 positive ions to enter the axon terminal.
The Axon terminal is part of the axon, the part of a motor neuron that neurotransmitters go through to get to the muscle. The axon terminal is a part of it that branches off and reaches into the muscle.
This will then stimulate some synaptic vessels to release the neurotransmitters by fusing it with the cell membrane..
The specific neurotransmitter released is acetylcholine.
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