Neurology question: Signals moving along nerve cells.

[unapologetic]

Neurology question: Signals moving along nerve cells.
(if this is the wrong forum, please point me to a better one)

First, I would like to clear-up my own understanding.
(a) Within nerve cells - As I understand it, signals move from one end of the cell to the other via electric pulses.
Is that correct?
(b) between nerve cells - As I understand it, Molecules of neurochemicals carry the signal across the gap between cells.
Is that correct?

Neurology question: Signals part 2
What happens to these molecules of neurochemicals, after they have carried their signal across the gap between nerve cells?
Are the neurochemicals absorbed by the receiving cell?
Are they retained by the receiving cell? Do they build-up?
Do they dissolve, or break-down, or get washed away?
Do they return to the originating cell?
Do they get re-used? Return to the original cell when a signal goes back the other way?

I have never heard an explanation of what happens next, to the neurochemicals. As if they've done their job, forget about em.
I think that is a mistake.
I'll explain why, after I improve my own understanding.

Thank you for your help.

 

[Jokodo]

https://en.m.wikipedia.org/wiki/Neurotransmitter#Elimination might be a good start.

Or you could type something like "neurotransmitter life cycle" into Google Scholar. Don't be discouraged if the first couple of results are paywalled, you will find something freely available.

 

[Jokodo]

I have never heard an explanation of what happens next, to the neurochemicals. As if they've done their job, forget about em.

Have you looked?

I think that is a mistake.

What is? Not looking and assuming no-one cares?

 

[Politesse]

I have never heard an explanation of what happens next, to the neurochemicals. As if they've done their job, forget about em.

Have you looked?

I think that is a mistake.

What is? Not looking and assuming no-one cares?

That's a surprisingly aggressive way to admit you don't know the answer.

 

[Politesse]

What happens to these molecules of neurochemicals, after they have carried their signal across the gap between nerve cells?
Are the neurochemicals absorbed by the receiving cell

So, they must be eliminated in short order, otherwise they'd continue affecting everything around them. But a couple of things can happen to them as the synaptic cleft is vacated, so the answer is really all of the above. Some just diffuse away, blurped into the mass of astrocyte glial cells that themselves activate where there is a lot of neuronal activity. Some are actively broken down by enzymes, some of which are aimed at specific neurotransmitters. And some do in fact get re-absorbed into the parent axon and stored for reuse, a process called "reuptake". Many anti-depressives work by specifically targeting re-uptake. Reuptake is the R in SSRI, for instance. So no, I'm afraid you haven't made a groundbreaking discovery, but the good news is that we already have many practical benefits from the study of this issue.

 

[Jarhyn]

Yeah, the dendrites that spit the signal to the axon terminal recapture the neurotransmitters. Their own surfaces have electromagnetic affinity to the transmitters they release, and any functional ones that remain get up-taken and all the broken ones either get up-taken and metabolized or destroyed by proteins that hunt free radicals like that. See also "reuptake".

Another element is that neurons have a temporal function as well, insofar as that when one activates the reuptake and reset time is an important part of the function because it allows things like "what you get when you dig deeper than the surface" sorts of concepts being perceived as qualia from the action of such a mechanism.

Neurons have a number of different aspects in which they achieve computational action and this is actually a very important one.

 

[Jokodo]

I have never heard an explanation of what happens next, to the neurochemicals. As if they've done their job, forget about em.

Have you looked?

I think that is a mistake.

What is? Not looking and assuming no-one cares?

That's a surprisingly aggressive way to admit you don't know the answer.

I'm no expert in neurochemistry. But asking a question that quick look at the Wikipedia page on neurotrsnsmitters will answer while insinuating that the experts aren't asking the right questions and I can set them straight seemed rather preposterous. Apologies if I'm misinterpreting @unapologetic , but that's the vibe I picked up.

 

[unapologetic]

I have never heard an explanation of what happens next, to the neurochemicals. As if they've done their job, forget about em.

Have you looked?

I think that is a mistake.

What is? Not looking and assuming no-one cares?

I am looking here cus I don't know where.

 

[unapologetic]

I'm afraid you haven't made a groundbreaking discovery,

Don't accuse me of that. I haven't claimed ANYTHING. I'm asking questions.

 

[unapologetic]

"insinuating that the experts aren't asking the right questions"
My apologies, I'm suggesting that publicly available documentaries never EXPLAIN it to my satisfaction. They stop with just the transmission and ignore the reuptake.
"... and I can set them straight" I never said any such thing. You are being far too sensitive, to mere questions.

 

[Jokodo]

I'm not familiar with what documentaries (which is I assume videos) do or do not tell about neurotransmitters. When I want to learn about a topic I'm unfamiliar with, I go for written sources. To someone with my approach, asking a question that Wikipedia answers accessibly right under "neurotransmitter" does smell of not having looked.

I am sorry if you feel misrepresented. I still wonder what that mistake is about?

 

[Jarhyn]

So, to your prior statements, I am not personally one who studies the molecular structures of the proteins. I do know a rather close friend who I could deliver your questions to who is, and they would probably tell you about as much as I'm going to tell you now:

The outer layer of the nation is composed of a lipid outer layer, and in the dendrite is an organelle of the cell that contains a high concentration of neurotransmitters.

When this organelle receives a signal from the sodium ion channel (essentially a tiny electrolytic wire), it causes the surface to yeet* the neurotransmitters out.

Some of them will break when being launched, some will probably stick to their attached protein (assuming that's how it works). They're tiny mole ular trebuchets.

These are rotated onto the cellular surface or have companion proteins that are such that when the axon terminal is done with the protein, it will yeet it back at the dendrite. The dendrite's surface then has the neurotransmitters get caught by the surface proteins, and the system gets reset.

In this process some will snap or twist funny, some will burn up in the oxygen-rich environment, and some will end up getting shot into the cell and not surviving the trip. Once they are there, the ATP of the cell has to take a moment to reset the triggers, and if it fires again too soon on that dendrite, it won't actually achieve a full launch and some of the process that does the launch will waste energy.

Some proteins likely exist that deliver wayward neurotransmitters back to places they belong, or they may have digestion proteins made to break up the lost neurotransmitters. This is in fact a part of the process whose effects are responsible for creating the signal of hunger from from the gut, and for tweaking our emotions in ways associated with the gut hormone and neurotransmitter serotonin via availability of it's precursor. The result is a particular signal that can be heard by the brain to trigger eating, accomplished through the limited halflife of serotonin and the availability of it's precursors.

I'm sure there are many important gut hormones and molecular signals that double up in this way, as a way of regulating resources.

The body is full of all sorts of interesting molecular contraptions. The ones involved here are much like the protein fuzz on the outside of a y cell that identifies, captures, and pulls in useful molecules through the cell wall, just specialized to do this very quickly with fairly fragile chemicals.

When too much activity happens, you can end up damaging the system long term; serotonin receptor agonists, such as MDMA, can cause long term damage to the neurotransmitters through overuse and this in turn causes detection via proteins and down-regulation of the process.

Essentially think of it as a game of catch where one side always throws back fairly promptly. They are called receptors, but they will get charged with ATP and as soon as the potential goes, they will send the neurotransmitters back pretty firmly, and there will be an electromagnetically active configuration on it that draws it promptly onto the dendritic terminal.

You can imagine it as a pair of really small, very weird trebuchets on walls playing catch.

*throw, launch, send, for any of the older folks here

 

[bilby]

(a) Within nerve cells - As I understand it, signals move from one end of the cell to the other via electric pulses.
Is that correct?

Yes. But no. But also, yes.

It would be a serious oversimplification to think of an axon as just:

essentially a tiny electrolytic wire

As always in biology, the reality is more complex than that. An axon transmits signals as a wave of ionisation reversal across its membrane. This is mediated by proteins embedded in the membrane, which act as 'gated channels' for potassium or sodium ions. The electrical potential difference across the membrane dictates when these channels are open, and the flow of these ions creates a change in electrical potential, which dictates when the channels open, which creates a change in potential... .

The result is a 'wave' of reversed electrical polarity across the membrane, which travels down the axon. The polarity reversal triggers polarity reversal, so at the front of the impulse, the positive charge outside the membrane and negative charge inside swap places; And at the back of the impulse, they swap back again.

This process can be stimulated by applying an electric charge to the axon, so neurosurgeons can use electricity to make nerve cells 'fire', but the signal isn't like in a wire, where loosely bound electrons are flowing through a metallic substrate to carry charge along the length of the wire; Rather the charges flow into and out of the "wire" at right angles to the direction in which the signal propogates.

Having said which, you should still remember that, as always in biology, the reality is more complex than that.

 

[unapologetic]

OK thanks guys, nuf said.

 

[BSprite]

Belated addition, despite the OP saying "done."

I don't have an "answer" because the questions in the OP are broad. However, there are two subject areas which provide some insight into signal transmission and homeostasis that I recommend glancing at. First, the interplay between dopamine and adrenaline/epinephrine in the acute stress response is an elegant model for neurotransmitters guiding biology. Second, there's some interesting work coming out of Northwestern looking at "valence assignment" in the amygdala being driven by neurotensin. Without getting into the substance of the work, it basically describes how neurotransmitters assign positive or negative value to memories. Unfortunately, the latter example doesn't get into turnover, spatial expression, or maintenance. The work does raise interesting questions along those lines.