Biology question on synapses! Watch

Cheeese589
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Hey

I need help.... with synapses, the arrival of an action potential at the synaptic knob causes calcium channels to open and calcium ions to enter the synaptic knob, is this by diffusion? the book is vague :/ im guessing yes?

Similarly does the acetlycholine diffuse across the synaptic cleft? im guessing yes also, but i need someone to confirm it,

thanks alot !
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Clumsy_Chemist
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I'm too tired to reach across to my biology book, but as far as I know yes it's diffusion if it's using an embedded channel protein then I think it's "facilitated diffusion". If it were active transport instead they'd be talking about "pumps" not "channels"
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Revd. Mike
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(Original post by Cheeese589)
Hey

I need help.... with synapses, the arrival of an action potential at the synaptic knob causes calcium channels to open and calcium ions to enter the synaptic knob, is this by diffusion? the book is vague :/ im guessing yes?

Similarly does the acetlycholine diffuse across the synaptic cleft? im guessing yes also, but i need someone to confirm it,

thanks alot !
Ca2+ concentration outside the cell (and within intracellular stores) is around 1000uM/1mM, whereas within the cytosol it's as little as 100nM; this provides a huge concentration gradient. When the depolarization arrives at the synaptic knob it opens the Ca2+ channels, allowing Ca2+ rapid entry.
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Clumsy_Chemist
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(Original post by Revd. Mike)
Ca2+ concentration outside the cell (and within intracellular stores) is around 1000uM/1mM, whereas within the cytosol it's as little as 100nM; this provides a huge concentration gradient. When the depolarization arrives at the synaptic knob it opens the Ca2+ channels, allowing Ca2+ rapid entry.
The question was whether this is diffusion, is it?
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Bslforever
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(Original post by Clumsy_Chemist)
The question was whether this is diffusion, is it?
Lol, what the good Revd. was trying to say in plain english was yes.

Yes it is.
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Revd. Mike
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(Original post by Clumsy_Chemist)
The question was whether this is diffusion, is it?
Via calcium channels.
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Vib-Rib
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Its a combination of diffusion (facilitated diffusion) and electrostatic repulsion. I think it's too simple at A level too say it's just diffusion you have to understand that the positively charged Ca is forced away from other positively charged ions.
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Revd. Mike
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(Original post by Vib-Rib)
Its a combination of diffusion (facilitated diffusion) and electrostatic repulsion. I think it's too simple at A level too say it's just diffusion you have to understand that the positively charged Ca is forced away from other positively charged ions.
Entry of Ca2+ into the cell isn't terribly complicated once the channels have opened. There's an overwhelming electrochemical gradient across the membrane.
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Rainbow249
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Both are diffusions, yes.
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John Locke
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(Original post by Vib-Rib)
Its a combination of diffusion (facilitated diffusion) and electrostatic repulsion. I think it's too simple at A level too say it's just diffusion you have to understand that the positively charged Ca is forced away from other positively charged ions.
where is there facilitated diffusion? its predominantly the opening of Cav2.2 channels carrying an N-type current that allows movement of calcium from its high extracellular concentration into the low concentration in the bouton.
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Vib-Rib
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(Original post by John Locke)
where is there facilitated diffusion? its predominantly the opening of Cav2.2 channels carrying an N-type current that allows movement of calcium from its high extracellular concentration into the low concentration in the bouton.
Ummmmm big words......

Isn't facilitated diffusion when something diffuses through a protein channel in the cell membrane and when the protein channel only lets one type of molecule, ion etc. through?

Is that not what happens during an action potential?
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John Locke
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(Original post by Vib-Rib)
Ummmmm big words......

Isn't facilitated diffusion when something diffuses through a protein channel in the cell membrane and when the protein channel only lets one type of molecule, ion etc. through?

Is that not what happens during an action potential?
reviewing my own definition of facilitated diffusion (FD) i suppose it is, i normally only really think of it being FD when conformational changes are involved but channels are count i guess. Once you get past A level nobody ever really talks about those kinds of definitions. not too sure about the single ion/molecule definition though, for example muscle subtype inotropic acetylcholine receptors (the main type involved in excitation-contraction coupling at the neuromuscular junction) are only cation selective not specific to say Na+. yet those are protein channels and so would be considered in the same category as a Ca++ channel?
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