Why are there so many neurotransmittrs?

[Elrog]

I have yet to find an adequate explanation to this question: "Why are there so many neurotransmitters?". It makes sense to me to only use the neurotransmitter that transfers the signal the fastest.

I would also like to ask a few other brief questions just for clarity.
Can multiple different kinds of neurotransmitters be found within a single synaptic knob?
Can multiple different kinds of neurotransmitters be found within a single neuron?

Here is a very typical, common response: "Different kinds of neurotransmitters are used to transmit different types of information (i.e. touch, taste, sight)".
This does no good unless you can show how the information is distinguished from other information every step of the way. As information travels through the axon as an electrical signal, does it still have a specific identity? Does a specific neurotransmitter being released trigger the next neuron to release the same neurotransmitter? The only way that could be possible is if a single axon acted as if it contained multiple wires rather than just being a single wire. From my understanding, that is not the case.

Here is another common answer: "Different neurotransmitters are used to avoid getting mixed signals".
I also don't see why mixed signals would occur if since the process of one neuron signaling another takes place within the synapses. I will accept this as an answer if it can be shown that a sufficient number (in relation to the amount required to fire the neuron) of neurotransmitters actually do escape the synapse and wind up in another synapse.

Another answer I came across is that the body has a use for neurotransmitter that act slower. For example: sustaining moments of (insert a feeling) for longer periods of time.
Generally this role is given to hormones as they would accomplish this better, and even with that said, your actual experience only happens in hindsight. Whether an experience feels longer or not doesn't necessarily have to do with how instantaneously you experienced it, it has to do with how much information about that experience was committed to your memory.

So which is it, or is it something else entirely?

 

[jim mcnamara]

Hmm. Interesting point of view. However, similar questions have been asked: why do humans have five fingers?

Evolution works with what it has available; species of Homo differentiated from other hominins early on and later from each other over long periods of time. Our common ancestors have and some living relatives still do have five digits. For that matter canids have five digits - one, the dewclaw, has retreated almost into oblivion.

Primates and humans also "share" neurotransmitters why? Because that was what was available. Some features that were available way back then, went the way of the dewclaw.

Evolution is not a logical process, it is an emergent process.

 

[atyy]

Can multiple different kinds of neurotransmitters be found within a single neuron?

http://www.ncbi.nlm.nih.gov/pubmed/20081852
http://www.ncbi.nlm.nih.gov/pubmed/20554874
http://jgp.rupress.org/content/139/1/93.full

 

[atyy]

"Why are there so many neurotransmitters?"

There are some exceptions to the following (see the post above), but here is the rule of thumb.

For the "classical", "fast" neurotransmitters each neuron releases only one type. Glutamate, the most common excitatory neurotransmitter in the brain, excites the postsynaptic neuron. So we need at least one other type of neurotransmitter to silence neurons (so that we can have + and - in the computation). The inhibitory neurotransmitters in the brain are glycine and GABA.

There are also slow neurotransmitters. Usually, these are conceived as acting over a long time scale, and acting on a volume of brain containing many neurons. These have partially overlapping but also different functions. I find these very complicated (maybe madness has a better view, since I believe he studied the anterior cingulate). For example, dopamine is involved in Parkinson's where I usually think of its action as "motor", but we also believe dopamine acts as a "reward" or "reward prediction error".

The current framework for dopamine in reinforcement learning is very good although it undoubtedly has problems. An overview is given in http://www.princeton.edu/~yael/Publications/Niv2009.pdf.

Your can get an idea of the complexity of other slow neurotransmitters like serotonin by looking up the history of anti-depressants.

 

[atyy]

"Why are there so many neurotransmitters?"

To add to jim mcnamara's post, you can google "neurotransmitter evolution".

Perhaps it's a bit like asking why there are so many programming languages.

 

[Elrog]

Thank you for the replies. Things are starting to become clearer. I also came across the term neurohormones (I suspect this is what atyy was referring to). Just one more question, how many neurotransmitters are also neurohormones? Thanks in advance.

 

[atyy]

Thank you for the replies. Things are starting to become clearer. I also came across the term neurohormones (I suspect this is what atyy was referring to). Just one more question, how many neurotransmitters are also neurohormones? Thanks in advance.

Neurohormones and the "non-classical" neurotransmitters are different.

Examples of "classical" neurotransmitters are glutamate, glycine and GABA. These act very specifically in the synaptic cleft of the pre-synaptic neuron to the post-synaptic neuron.

Examples of "non-classical" neurotransmitters are dopamine, acetylcholine and serotonin. These are spewed all over a large area (compared to the classical neurotransmitters which act in a synaptic cleft) in the cerebrospinal fluid of the brain.

Neurohormones are typically different from the non-classical neurotransmitters in that they are released into the blood (as opposed to the cerebrospinal fluid in the brain).

Wikipedia https://en.wikipedia.org/wiki/Neurohormone notes that some of the neurohormones are also neurotransmitters because they are also released into the cerebrospinal fluid in the brain.

As usual, terminology may vary, so don't get too hung up if you see slightly different usages.

 

[fredreload]

This might be a bit of a broader question but, neurotransmitter is part of the chemical synapse. Is our consciousness made up of chemical synapse, electrical synapse, or both, based on the current finding?

 

[jim mcnamara]

human - a bag of way more than 100000 molecules and a large number of chemical reactions. So to answer your question - there is not really a best approximation. Right now. In other words you could very well argue either position. There is simply too much going on.

The reason biology has 'taken off' is the ability to quickly enumerate the base pair sequences in DNA, which is predictive. Anything predictive in Biology is a big plus for research - and utimately generating the big picture - the answer to your approximation question. So check back in about 10 years.

 

[atyy]

This might be a bit of a broader question but, neurotransmitter is part of the chemical synapse. Is our consciousness made up of chemical synapse, electrical synapse, or both, based on the current finding?

Unknown. Most models of cortical function ignore electrical synapses, and a lot can be explained without electrical synapses. But electrical synapses are important in the retina, eg. http://www.ncbi.nlm.nih.gov/pubmed/22399777. And there are some theories as to how they may be important in the brain, eg. http://www.ncbi.nlm.nih.gov/pubmed/23596411.

 

[fredreload]

My guess is the difference in speed, synaptic delay for electrical synapse is 10x faster than that of chemical synapse according Wikipedia. Hopefully something productive will be done in the next 10 years.

 

[Elrog]

It occurred to me that a slower acting neurotransmitter may be more efficient, which would explain its selective usage.

Another thing that came to mind is having a neurotransmitter be a hormone also could be more efficient because you only need to produce one type of molecule and you can use it for either a hormone or a neurotransmitter.

Is there any information out there linking different kinds of neurotransmitters to different levels of energy consumption?

 

[jim mcnamara]

Do you mean a bioenergetics approach to the selection of neurotransmitters - then consider glutamate. It is the salt of the amino acid glutamine. Animals routinely consume glutamate-bearing foods - so your neurotransmitter is simply the salt of a proteolysis product. Sort of a "free" byproduct energy-wise. Glutamate is the 'major excitatory neurotransmitter in the brain'. So in a sense this approach, bioenergetics, can be used to explain 'why glutamate?' And natural selection favored this molecule long, long ago.

http://neurotransporter.org/glutamate.html

 

[fredreload]

Well to understand consciousness we can first by examining the sense of touch to the central nervous system. From my perspective, the neurons work sort of like a transistor . Yes this should be how transistors add numbers, but in our case the central nervous system with the neurons would form logic gates good enough to sense touch, using OR and AND gates, based on how our central nervous system process information. If someone has other explanation, possible through chemical synapses or the idea about how central nervous system process information, feel free to let me know.

P.S. But air can't feel pain welp, someone correct my logic.

 

[fredreload]

To clarify, you can make consciousness feel pain but probably not anything else.

P.S. Does that make human consciousness something like an output?

 

[fredreload]

An analog output.

 

[fredreload]

It's all 0 and 1 right base on if there is current input or not. So assuming there are thousands of connections onto a neuron it would represent the states as something like a 1010101010010 type of number with current going in and out like the video.

 

[fredreload]

Hmm, according to neural transmission the binding of the neural transmitter may be either inhibitory or excitatory, is that also caused by the type of neural transmitter there is?

 

[atyy]

Hmm, according to neural transmission the binding of the neural transmitter may be either inhibitory or excitatory, is that also caused by the type of neural transmitter there is?

"Essentially" yes. But you can study this exception to learn more: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2096719/. There you will see that GABA, which is "generally" an inhibitory neurotransmitter, can be excitatory.

DuckDuckGo also suggests http://www.jneurosci.org/content/32/2/572.short.

 

[Laroxe]

I think atyy's link to http://jgp.rupress.org/content/139/1/93.full is an interesting read, but the basic answer must be we don't really know, in fact its unlikely we have a clear idea of all the different effector substances that act on nerves. Remember that nerves either fire or they don't, that's it, its an all or nothing response, a switch in effect and in the brain a single nerve can directly interact with up to 10.000 others and is sat in a chemical bath. So there are lots of things attempting to modify the nerves action potential. If you really want to have fun, it might be more productive to look at receptor sites rather than the chemicals that act upon them. Nerves are covered with them and react to all sorts of things, different nerves may even react to the same effector substance in quite different ways. Even within the synapse there are multiple types of receptors for the same transmitter substance. Interestingly many of the same chemicals that are used as transmitters or modulators in the brain are produced and have quite different functions in the rest of the body, most being unable to cross the blood brain barrier. I suspect the only sense in all of this as multiple people suggest is in our evolutionary history, it would be fun trying to get someone who believes in "intelligent design" to explain it all.

 

[fredreload]

I believe how brain works is similar to that of a computer. The part where the computer CPU seems to think and is providing an output to the screen. The brain also resembles that of a computer and the consciousness is generated within the circuit structure itself. So the circuit structure itself should be able to generate a consciousness. We are just in the process of uncovering it. Even the smallest organism with 300 neurons is capable of reacting to stimuli. Well, but this is speculation on my part. How the consciousness is generated and how the touch sensation arises remain a mystery at this point.