Kayleejarv24
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hi, I am stuck on a question it needs to be 450 word my question is explain how a nerve impulse is transmitted, including the transmission across the junction between one neurone and the next.
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username4933904
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(Original post by Kayleejarv24)
hi, I am stuck on a question it needs to be 450 word my question is explain how a nerve impulse is transmitted, including the transmission across the junction between one neurone and the next.
you want someone to write the answer for you?
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Kayleejarv24
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(Original post by HumblyBumbly)
you want someone to write the answer for you?
no course, not I'm not a cheat lol, just a bit of help with the question I know a little bit but not much to write 450 words.
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macpatgh-Sheldon
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Hi Kayleigh [hope you are well - it's a while],

In a way, Bubbly is right, but he/she is not aware of your major problems including changing nappies () and the family tragedy, so I will try to help you out.

I shall try to give you some keywords to look up (actually 450 words is far too short to cover the detail properly).

I would start with explaining the basic structure of a neurone and the creation of the resting potential (including the Na+, K+ - ATPase pump) then define pre-synaptic and post-synaptic neurones, and talk about the synapse.

Then go through the concepts of All-or-none phenomenon, threshold and action potential; describe nodes of Ranvier [and how they enable saltatory conduction] and the production of the myelin sheath by Schwann cells plus function of myelin.

You can mention the main categories of neurones based on the speed of conduction [which depends on their cross-sectional diameter (A fibres, A-alpha, etc.]

Then go through neurotransmitters (acetylcholine, noradrenaline [norepinephrine in US], dopamine, glycine, GABA) and their diffusion across the synapse, plus action on receptors (muscarinic, nicotinic, adrenoceptors (alpha and beta) and the importance of calcium ions in the process of generation of the EPSP or IPSP.

Google the words in bold.

Good luck!

M.

PS I shall try to upload some beautiful pics for u in a sec.
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macpatgh-Sheldon
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Kayleejarv24
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Thank you very much I really appreciate it I have done it. But not sure if I have covered the question in what I have written just hope I have lol👍
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Amanda *M*
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Hi, I’m doing the same sort of thing. Can I ask - how does repolarisation return the membrane potential to negative? Because all of the potassium ions are out of the cell? I get the depolarisation bit, but the definition of repolarisation doesn’t make sense to me?

thanks
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macpatgh-Sheldon
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Hi Amanda good morning (wakie wakie!)
btw you must be my boss (Sheldon is not my only alias - also known as 007! )

Let me explain: firstly, the fundamental idea to understand.is that the negative resting potential at rest and the changes during the action potential are ALL RELATIVE i.e. inside compared to outside the neurolemma, so try NOT to think in terms of "all K+ ions out of cell".

OK now to your actual Q:- Repolarization occurs mainly due to opening of voltage-gated K+ channels, which means there is K+ efflux [movement of K+ out of the neurone], leaving the inside RELATIVELY negative once again. If you are aiming for A* (everyone should be as ALL my private students do [and succeed]!), then it might be worth knowing that repolarization is also partly contributed to by the fact that the gradient for Na+ at this point in time is reducing, simply because of the fact that Na+ has rushed in during the upstroke of the action potential, so that Na+ entry is slowing down considerably (ONCE AGAIN, remember all this is relative).

Just one extra point (not part of your Q): K+ channels opening is a much slower process than that of Na+ channels so that:
a) the repolarization downstroke is less steep than the depolarization upstroke.
b) this explains hyperpolarization in that the slow return of K+ channels to the closed state that concludes repolarization, results in the potential overshooting the normal resting value of -70 mV.

I am going to upload a lovely pic in a sec for you.

M
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macpatgh-Sheldon
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Amanda *M*
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(Original post by macpatgh-Sheldon)
Hi Amanda good morning (wakie wakie!)
btw you must be my boss (Sheldon is not my only alias - also known as 007! )

Let me explain: firstly, the fundamental idea to understand.is that the negative resting potential at rest and the changes during the action potential are ALL RELATIVE i.e. inside compared to outside the neurolemma, so try NOT to think in terms of "all K+ ions out of cell".

OK now to your actual Q:- Repolarization occurs mainly due to opening of voltage-gated K+ channels, which means there is K+ efflux [movement of K+ out of the neurone], leaving the inside RELATIVELY negative once again. If you are aiming for A* (everyone should be as ALL my private students do [and succeed]!), then it might be worth knowing that repolarization is also partly contributed to by the fact that the gradient for Na+ at this point in time is reducing, simply because of the fact that Na+ has rushed in during the upstroke of the action potential, so that Na+ entry is slowing down considerably (ONCE AGAIN, remember all this is relative).

Just one extra point (not part of your Q): K+ channels opening is a much slower process than that of Na+ channels so that:
a) the repolarization downstroke is less steep than the depolarization upstroke.
b) this explains hyperpolarization in that the slow return of K+ channels to the closed state that concludes repolarization, results in the potential overshooting the normal resting value of -70 mV.

I am going to upload a lovely pic in a sec for you.

M
Thanks - i get it a bit better now.

after hyper polarisation - do the sodium ions go back to where they were before? (mostly outside the cell), and the potassium go back inside the cell?

Thanks
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macpatgh-Sheldon
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Hi glad that I was of help. I would not worry too much about the fate of the ions after an action potential cos out of the large pool of extracellular Na+ ions and intracellular K+ ions, extremely few move to change the internal potential of a neurone e.g. it is estimated that 1 in 100,000 K+ ions are extruded to change the action potential of a neurone from +30 mV [peak of action potential] to -70 mV [back to resting potential].
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