Neuromuscular junction

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(Created page with 'A neuromuscular junction is a type of synapse, a gap between a neurone and the muscle end plate. At a neuromuscular junction an [[action potential|action potenti…')
 
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A neuromuscular junction is a type of [[Synapse|synapse]], a gap between a neurone and the muscle end plate. At a neuromuscular junction an [[action potential|action potential]] passes from the presynaptic membrane to the postsynaptic membrane on the muscle end plate. This is to allow information to pass from neurone to muscle end plate which will result in the relaxation or the contraction of the muscle.
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A neuromuscular junction is a type of [[Synapse|synapse]], a gap between a [[Neurone|neurone]] and the [[Muscle end plate|muscle end plate]]. At a neuromuscular junction an [[Action potential|action potential]] passes from the [[Presynaptic membrane|presynaptic membrane]] to the [[Postsynaptic membrane|postsynaptic membrane]] on the muscle end plate. This is to allow information to pass from neurone to muscle end plate which will result in the relaxation or the contraction of the muscle.  
  
In order for this action potential to be passed on to the postsynaptic membrane several steps occur:
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In order for this action potential to be passed on to the [[Postsynaptic membrane|postsynaptic membrane]] several steps occur:  
  
1. An action potential (generated by a [[Graded_potentials|graded potential]]) arrives at the axon terminal. This causes the [[depolarisation|depolarisation ]]of the presynaptic membrane which is important for the opening of the voltage-gated calcium channels.
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#An [[Action potential|action potential]] (generated by a [[Graded potentials|graded potential]]) arrives at the [[Axon|axon]] terminal. This causes the [[Depolarisation|depolarisation]] of the presynaptic membrane which is important for the opening of the voltage-gated calcium channels.  
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#[[Calcium|Calcium]] [[Ions|ions]] move down their concentration gradient into the presynaptic membrane causing [[Vesicle|vesicles]] containing the [[Neurotransmitter|neurotransmitter]] [[Acetylcholine|acetylcholine]] (the most common [[Neurotransmitter|neurotransmitter]]) to fuse with the presynaptic membrane.
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#The neurotransmitter [[Acetylcholine|acetylcholine]], then diffuses across the [[Synaptic cleft|synaptic cleft]] and binds to the specific receptor [[Proteins|proteins]] on the postsynaptic membrance, the muscle end plate.
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#When this happens, it causes the [[Ligand|ligand]]-gated sodium channels to open.
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#[[Sodium|Sodium]] [[Ions|ions]] diffuse down their concentration gradient into the postsynaptic membrane. This causes the depolarisation to be passed on to the muscle end plate, and the action potential continues.
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#To close the [[Ligand-gated sodium channels|ligand-gated sodium channels]] and stop the depolarisation of the muscle end plate, an enzyme called [[Acetylcholinesterase|acetylcholinesterase]] binds to [[Acetylcholine|acetylcholine]] and breaks it down into [[Choline|choline]] and [[Acetate|acetate]]. These are then recycled back into the presynaptic membrane to be used again.<br>
  
2. Calcium ions move down their concentration gradient into the presynaptic membrane causing [[vesicle|vesicles]] containing the neurotransmitter acetylcholine (the most common neurotransmitter) to fuse with the presynaptic membrane.
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These are the steps that occur at a Neuromuscular Junction&nbsp;<ref>Alberts, Johnson, Lewis, Raff, Roberts, Walter; Molecular Biology of the cell, fifth edition; page 687-688, Garland Science</ref>&nbsp;<ref>Boyle and Senior, Biology, Collins Advanced Science, second edition, pages 354-357</ref>.
  
3. The neurotransmitter. acetylcholine, then diffuses across the synaptic cleft and binds to the specific receptor proteins on the postsynaptic membrance, the muscle end plate.
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=== References ===
  
4. When this happens, it causes the [[Ligand|ligand]]-gated sodium channels to open.
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<references />
 
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5. Sodium&nbsp;ions diffuse down their concentration gradient into the postsynaptic membrane. This causes the depolarisation to be passed on to the muscle end plate, and the action potential continues.
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6. To close the ligand-gated sodium channels and stop the depolarisation of the muscle end plate, an enzyme called acetylcholinesterase binds to acetylcholine and breaks it down into choline and acetate. These are then recycled back into the presynaptic membrane to be used again.
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These are the steps that occur at a Neuromuscular Junction.
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<ref>Alberts, Johnson, Lewis, Raff, Roberts, Walter; Molecular Biology of the cell, fifth edition; page 687-688, Garland Science</ref>
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<ref>Boyle and Senior, Biology, Collins Advanced Science, second edition, pages 354-357</ref>
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Revision as of 17:41, 21 November 2010

A neuromuscular junction is a type of synapse, a gap between a neurone and the muscle end plate. At a neuromuscular junction an action potential passes from the presynaptic membrane to the postsynaptic membrane on the muscle end plate. This is to allow information to pass from neurone to muscle end plate which will result in the relaxation or the contraction of the muscle.

In order for this action potential to be passed on to the postsynaptic membrane several steps occur:

  1. An action potential (generated by a graded potential) arrives at the axon terminal. This causes the depolarisation of the presynaptic membrane which is important for the opening of the voltage-gated calcium channels.
  2. Calcium ions move down their concentration gradient into the presynaptic membrane causing vesicles containing the neurotransmitter acetylcholine (the most common neurotransmitter) to fuse with the presynaptic membrane.
  3. The neurotransmitter acetylcholine, then diffuses across the synaptic cleft and binds to the specific receptor proteins on the postsynaptic membrance, the muscle end plate.
  4. When this happens, it causes the ligand-gated sodium channels to open.
  5. Sodium ions diffuse down their concentration gradient into the postsynaptic membrane. This causes the depolarisation to be passed on to the muscle end plate, and the action potential continues.
  6. To close the ligand-gated sodium channels and stop the depolarisation of the muscle end plate, an enzyme called acetylcholinesterase binds to acetylcholine and breaks it down into choline and acetate. These are then recycled back into the presynaptic membrane to be used again.

These are the steps that occur at a Neuromuscular Junction [1] [2].

References

  1. Alberts, Johnson, Lewis, Raff, Roberts, Walter; Molecular Biology of the cell, fifth edition; page 687-688, Garland Science
  2. Boyle and Senior, Biology, Collins Advanced Science, second edition, pages 354-357
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