I'm going to drop off all my neural questions that books have so far not given me answers for.

Two neural signaling questions, which, if I'm not mistaken, haven't seen application in neural networks as yet, and one fMRI scan question:

1) "5-HT is thought to be released from serotonergic varicosities into the extra neuronal space, in other words from swellings (varicosities) along the axon, rather than from synaptic terminal buttons (in the manner of classical neurotransmission). From here it is free to diffuse over a relatively large region of space (>20µm) and activate 5-HT receptors located on the dendrites, cell bodies and presynaptic terminals of adjacent neurons." Norepinephrine, or so I've read, also tends to find itself swimming in the extra neural space (cerebrospinal fluid I believe?) and seeking out appropriate receptors or means of metabolic degradation.

Is the extracellular diffusion of serotonin and norepinephrine (i.e. aim axon at neural cluster, spray) considered to be the functional systematic cause of sensitization, say, with animals in shock therapy sessions? I would assume serotonin's 2nd messenger signal cascade transcripts proteins from DNA to grow new synapses which add more noise into the neural network. This would smooth out over time via positive/negative feedback and prune the synapses within the grander systems of LTP/LTD, synaptic scaling and metaplasticity.

Any thoughts as to why we haven't seen this modeled in neural networks? And slaps on the wrist for my logic are also welcome.

2) Dendritic branching is what gets me the most.

..................D
.....B........../.
A...|....C.../..
..\ /......\ /....
...\......../.....
....|...../.......
[Cell Soma]
.......||.........
.......||.........
.......||.........
....../|\.........

A,B,C,D symbolize synapses.

Do signals decay as they travel afferently toward the soma?
i.e. if synapse D gets a weak signal (EPSP), if the signal is weak enough, can it decay before it reaches the Cell Soma?

Can signals that encounter branches on their afferent way down toward the soma travel efferently up the encountered branch?
i.e. if synapse A recieves an Action Potential, will it travel towards the Cell Soma AND up the branch it encounters along the way to fire synapse B?

When any signal, whether bona fide action potential or merely an EPSP/IPSP reaches the Cell Soma from one Dendrite Trunk (the trunk holding Synapses A and B ), will it travel down the axon AND up other Dendrite Trunks (the trunk holding Synapses C and D )?

If this actually happens, wouldn't that create an exponentially perpetuating signal? Well, assuming there were cautiously maintained and balanced excitation/inhibition currents, maybe not. If this isn't the case, then I guess the ratio of ~1000 dendrites per one axon helps keep the signals specialized and efficient.

Not to mention Dendrites rarely have transmitters to release. But rarely doesn't mean never: [Search Pubmed for PMID: 37984 - (sigh) that's annoying that I'm not allowed to post URL links in this forum]

3) And one last thing.

fMRI scans show us the vaso-constriction/dilation of blood vessles feeding astrocytes and the rest of the blood/brain barrier, ultimately transport nutrients (amino acids to make monoamine transmitters, electrolytes, etc.) to neurons.

Does anybody know where the signal comes from that decides to flood specific areas of the brain with blood and not others?

Is this a chicken or the egg question? Do action potentials attract blood flow around them (sucking up oxygen for ion channel pumps), or do vasoconstricting Hormones (like Vasopressin) that are already in the blood expand/contract blood vessels in areas of the brain first?

And all stressed/anxious/concentrative mental states (not to mention amphetaminically and entheogenically induced states) raise (and sometimes lower) blood pressure.

Does a raise in blood pressure primarily speed up cell metabolism and that can be considered the cause for the unusual feeling of "heightened senses" we find ourselves in when in a fight/flight situation or in a drugged state?

Or does a raise in blood pressure effectively make an fMRI scan generally more active. So that it's really the increase in Vessicle leakage into the synaptic cleft that accounts for the "heightened senses"?

look up dendritic spikes and back-propagating spikes.

I'm certainly not an expert, but let me take a stab at part three.

I believe fMRIs primarily measure the oxygenation of the blood. Oxygen is very electronegative, and creates a strong electron desheilding effect on neighboring hydrogen molecules that can easily be detected by an MRI as opposed to deoxygenated blood. Of course, blood volume (flow) can be deduced from this info.

When a neuron fires frequently, ATP is dephosphorylated into ADP to perform work. (Construction of transmitters, transport, NaK pump, etc)

Now, I'm not sure of the exact mechanism, but increased levels of ADP lead to more ATP production. Cells have very complex feedback regulation loops; the presence or absence of certain molecules often activates/deactivates other pathways

ATP production results from cellular respiration. As we know, this consumes O2 and produces CO2.

This, in turn, creates a concentration gradient across the cell favoring uptake of O2 and disposal CO2.

So, until equilibrium is restored, oxygenated blood will "rush" into the cell. I believe this is what the fMRI detects.

Do keep in mind that this process is not instantaneous. But it does happen very quickly.

The signal to increase blood flow comes from the action of firing itself.

Does that make sense?

And yes, the nervous system does control vasoconstriction as well. This is another factor in addition to the aforementioned one.

So, here's my answer:
Blood flow is determined by the parts of the brain firing. But, the brain can direct even more blood to specific areas if it so chooses.

Much thanks; I've since been googling and data mining those terms and confirming a lot of what I'd thought would have to be the case to explain those beautiful messes called dendrites. Not the sort of things that I've seen in any text books leading up to now. I imagine quite a good bit of routing logic and LTP owe their existence to this system.

On an unrelated note, do you know much about the phenominon of "neural oscillations"?

http://www.pnas.org/cgi/reprint/101/26/9849.pdf
http://www.bm-science.com/team/chapt3.pdf

The Fingelkurts brothers (2nd link) especially seem to be really heading down some fascinating paths for chipping away at the mysterious stone that is perception... or so I'd like to say and mean, but to be honest I'm having a tough time really visualizing what is meant by neural ensembles emitting oscillatory activity that synchs or desynchs.

Fantastic, this is just the detail I was lacking.

Now, don't ionotropic receptors do speedy ion-channel signaling without involving ATP/ADP and other metabotropic receptor functions? So wouldn't that mean fMRI scans detect the activity of only metabotropic signaling and not ionotropic signaling?

Are you suggesting that a neuron can fire with 100% efficiency? (i.e. no consumption or loss of energy)
I think a fundamental knowledge of physics can answer that question.

Don't forget that supporting cell functions consume energy as well (i.e. replenishing the supply of neurotransmitters and transporting them.)

Somewhere, somehow, ATP (or another energy source) will be consumed upon firing. This may directly involve the firing mechanism, or it may involve the cellular support functions.

Of course, there may be a difference in consumption between the two. But quite frankly, I can't give you a solid answer there.

My general point, though I do see now that I didn't word it properly, was that there would be a bias in the fMRI readings according to what I read into your definition of what the scan is picking up. Such that heavy processing areas of activity will be metabotropic and light processing areas would be ionotropic. So it may function as a better map as to where plasticity is having most of its fun at the moment than an EEG.

In truth, I have avoided physics classes, so I admit my capacity for problem solving is rather limited to basic logic and computer programming, and the bias I'm viewing the problem of neural networks with causes me to desire to condense the physiological into as neat a symbolic, mathematical package as I can. And maybe give it a nifty little Carmine ribbon too, with emerald lining. Yeah, that'd be nice.

Neural Oscillations? Simple, any electrical current will generate a frequency, the frequency is determined by the number of revolutions per second. Going into detail on how you generate an electromagnetic frequency in a non-conventional current is a time consuming process. I still have another 100 pages of Leonardos notebook to copy out by hand and then I have to see about translating a GIANT tome know as the Codex Altlantica written in 15th century Italian.

Neural Oscillating activity that syncs and de-syncs? Sigh* you need to learn more on electromagnetic theory and particle physics. Oscillations are when an electrical current moves throughout a circut. A freqeuency is how fast that current moves, the diffrence between a regular current and a neuroscience one is that the electrical current in the neurons doesnt vary... it always stays the same.

No the brain isnt a superconductor and yes it does have resistance, the reason it stays the same is because the neuron stores K+ and Na+, when it fires it opens 'gates' which allow the same amount of K+ and Na+ to be released every time. Think of it like you have a lot of tiny batteries and resistors in a circut, when an electrical signal passes the resistor and gets to the battery, the battery will release a certain amount of energy and send it to the next resistor.

Basically the K+ and Sa+ moving from one Axon to the Dendrite and then to the Cell Membrane. This causes that cell to fire and so the process continues. Remember K+ and Sa+ are positively charged ions (in case anyone doesnt know, ions occur when you have more or less electrons than in the atoms regular state).

Now I want you to think about this and post how you think all this comes together. I have no problem with people asking lots of questions, but I am going to show you how to solve these questions. If I just give you the answer, you wont learn anything, so instead im giving you the base of it and you can fill in the gaps.

Just start thinking in terms of electricity as well as neuroscience and youl be fine. Your problem is you are trying to fit neuroscience into a little box and it doesnt work that way. Everything affects the brain from biology to chemistry, physics to magnetic waves, if you try to use just neuroscience to understand how the brain works, you wont get anywhere. There are so many things to know like how magnetic waves form in the brain to how the brain releases diffrent chemicals based off of its psychological state. Oscillations deal with Physics - Electricity, go pick up a grade 12 physics book from the library and that should give you all the resources you need. It covers the bases and unless your taking physics or happen to be naturally good at physics, getting university text books on physics will probably just confuse you and waste your time.

Point taken. Now that you've kindly spelled that out to me, I can see how my questions have all been physics based. After all the time I've been pouring into cell physiology, genetic algorithm programming, and neural net concepts I've neglected the swords and shields of the neural quarrel settlers. Allow me to cast aside my stone based tools, my tail is firmly between my legs good sirs, and I retire back to my small tower perchance to emerge again when I give off fewer inferior pheromones. Good day.

+ .. Chinese Whispers?

Lol, exchange your stone tools for bronze ones

I look forward to your return, Good Luck.

neural oscillations are interesting because they are ubiquitous throughout the brain, though their functional significance is unclear. There have been suggestions that oscillations serve to synchronize neural activity, or that they are a type of carrier wave, but no-one knows for certain.