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I am interested in understanding what "pain" and "hot/cold" look like, as far as waves signatures (signal processing) go.

My general understanding of how pain (nociceptive pathways) and hot/cold (thermoreceptive pathways) works are as follows:

  • A sensory receptor (nociceptor for pain and thermoreceptor for temperature) responds to analog stimuli, and synapses an appropriate signal onto a first-order neuron (the neuron it directly connects to); then
  • The signal travels up the nerve, neuron to neuron, through the spinal cord, up into the brainstem, and finally into the somatosensory cortex; then
  • That cortex decodes the signal and interprets it as "pain" or "hot/cold"

Further, my understanding is that these signals are electrochemical in nature:

  • While passing through a neuron (dendrite -> axon) the signal is of a purely electrical form, no different than the electricity racing around the motherboard of my laptop right now; but...
  • To synapse from the axon of one neuron to the dendrite of the next sequential neuron, the electrical signal is transformed (somehow, this is where I'm fuzzy) into a chemical signal, and essentially hormones/messenger chemicals ferry the preserved signal to the next neuron's dendrite. At that point, the dendrite converts the chemical signal back into electricity, and on and on this goes until we reach the cortex.

So, only because I am a total neophyte here, I have to preface my actual question by asking the greater community at large: is my general understanding here correct? If not, please begin by correcting me!

The question at hand

If everything I've currently stated is more or less correct, then this implies that, while traveling inside a neuron (dendrite -> axon), neurological signals such as pain or temperature exist as waves of electricity.

I'm wondering:

  • What do these waves look like? Do they have special names? Are they sinusoidal in nature? Do they travel with known periods/frequencies/amplitudes? Can I represent these waves as trigonometric functions?
  • I'm sure this differs based on genetics and all sorts of other factors, but what are the general power ratings for the central nervous system? How much Watts/Volts/Amps travel with these signals? Are there standard ranges?

Please note: This is not homework! I am a grown man who works as a software engineer by day and I migrated here from the Stack Overflow community. I am asking this question because I have absolutely zero background in biology, and after scouring the internet for an answer to this, I could find nothing.

Please don't hold back with lofty, low-level explanations. Give me science here! Though I am not a biologist, I'm certainly no dummy either.

AliceD
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smeeb
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    "Can I represent these waves as trigonometric functions?" Not really.. You can have a look at Hodgkin-Huxley model or the FitzHugh-Nagumo model.. These are frequently used to model neural impulses.. These are not actually sinusoidal. You can also have a look at what is known as relaxation oscillator – WYSIWYG Dec 17 '14 at 19:05
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    Welcome to Biology.SE! You may want to have a look at action potential. – Remi.b Dec 17 '14 at 19:10
  • Thanks for the welcome Remi.b, and thanks for the links @WYSIWYG (+1 to both)! – smeeb Dec 17 '14 at 19:27
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    RE "This is not homework!..." if this is reference to a question which garnered close votes as "homework" you should note that the homework close vote is often used as closure on "poorly researched questions" not just homework (just in case you were a bit confused by this happening when it is not homework) – rg255 Dec 17 '14 at 19:40
  • Thanks @GriffinEvo (+1) - I don't have enough rep to see if my questions are even garnering closevotes or not :-) I put that disclaimer in there because I asked a previous question yesterday and I quickly received comments from other users who obviously assumed I was a student looking for a "quick answer". We get this all the time on Stack Overflow, and so I wanted to combat any potential nay-sayers right up front; hence the disclaimer. – smeeb Dec 17 '14 at 19:45
  • I wouldn't say that the signal in a neuron is the same as in your motherboard. Electrical current is the flow of charges (electrons) parallel to the wire. A nerve impulse is the flow of charges (cations) perpendicular to the nerve (which propagates a signal parallel). – canadianer Dec 17 '14 at 19:48

2 Answers2

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I don't want to comment about the nature of electric signals in neurons (as I know only little about physiology and neurophysiology). But here is a short answer that may already help you.

Neuronal electric signals are called action potential. If you register the voltage at a given location on the axon of a neuron through time you will see something like this:

enter image description here

This picture shows one action potential. Of course when you feel pain it lasts for more than 5 milliseconds. In such case, if you record the voltage for a longer period of time you will just see a series of action potentials. You should have a look to the wiki page for more information.

Remi.b
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  • Awesome answer, thanks @Remi.b (+1)! Quick followup question: say this graph above is what pain "looks" like as a wave. What about "pins and needles" (neuropathy) signals? Again, if my naive understanding of biology is correct, neuropathy occurs when a neuron ceases to function properly and sends junk/garbage signals on to the brain. The brain, in turn, can't make heads or tails as to what the signal is trying to convey, and so we experience the pins and needles sensation. – smeeb Dec 17 '14 at 19:24
  • So: (1) is the pins-and-needles "wave" a specific type of wave (distinct from the "normal" one above) that the brain knows to interpret as pins and needles, or (2) does the brain just interpret anything it doesn't understand as neuropathy? Thanks again so much! – smeeb Dec 17 '14 at 19:25
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    @smeeb there is no general difference in the waveform between types of perception. pain perceiving neurons are non-myelinated and are therefore slower in their conduction. – WYSIWYG Dec 17 '14 at 19:29
  • Hmm interesting @WYSIWYG (+1 and thanks) - but obviously the brain knows to interpret pain and pins/needles differently. So if these sensations don't differ by wave form, then how are the different (in other words, what is electrically-different about them that allows us to distinguish the sensations)? – smeeb Dec 17 '14 at 19:31
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    They come from different neurons. Analogy in that your two USB cables both conduct electricity, but the one connected to your hard disk has different information than your charging phone. – March Ho Dec 17 '14 at 19:31
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    Sorry, it is not my field of expertise, I am not able to tell much more. But the picture shows what basically any neuronal message looks like in term of voltage through time along the axon. Different tactile perception may use different neurons I think (pain, touch, warm/cold) but all of these neurons, always send message through the same kind of electric waves. – Remi.b Dec 17 '14 at 19:31
  • Thanks @MarchHo (+1) - what neurons do pins-and-needles come from? – smeeb Dec 17 '14 at 19:31
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    http://biology.stackexchange.com/questions/24555/what-causes-feeling-of-feet-falling-asleep-to-be-delayed/25856#25856 is an answer I recently put up on the origin of pins and needles. Consider reading the question and other answers too for a general overview. – March Ho Dec 17 '14 at 19:33
  • Thanks again @MarchHo (+1) - I'll dig in more tonight, and I appreciate your USB analogy. But to summarize: are you saying: (1) that "pins and needles" (parasthesia/neuropathy) travels to the brain with the same waveform as any other signal but simply carries different encoded "data" on it; or are you saying that (2) there are special neurons that specifically transmit parasthesia signals to the brain? And if, #2, then I'm curious: what are the names of these specialized neurons? Thanks again! – smeeb Dec 17 '14 at 19:42
  • What is important is the sequence of action potentials. I would suggest reading about temporal coding and rate coding as a start. For instance a (very lightweight) introduction can be found on Wikipedia: http://en.wikipedia.org/wiki/Neural_coding Also, note that much of it is how we INTERPRET a certain neuronal signal; our brain is easily fooled! For instance, when eating spicy food we perceive it as "hot", even if it is not at high temperature. This is because the receptors mediating the "hot" sensation are the same for spice and temperature. – nico Dec 26 '14 at 09:36
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Since the action potential question has already been answered, I will attempt to answer

I'm sure this differs based on genetics and all sorts of other factors, but what are the general power ratings for the central nervous system? How much Watts/Volts/Amps travel with these signals? Are there standard ranges?

You are right in that there is a large amount of variation in the electrical variables, however neurons generally have an action potential voltage of ~70mV, give and take 30. I could not find any papers in a cursory search on the power of neurons.

To answer your "comment question" due to lack of space, (1) neurons encode data in a binary fashion due to their on or off mechanism of impulse transmission, and there have been studies done in deciphering what these pulses mean. However, it is still an active field of research with many questions. (2) However, pain signals are only transmitted on sensory neurons containing nociceptors.

You should also read up on how an action potential is generated, as that would help you understand the concept better.

March Ho
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  • Thank you so much @March Ho (+1) - last followup question (I promise), and it should get to the root of my question here: if pain signals are only transmitted on sensory neurons containing nociceptors, then what is the equivalent for "pins and needles" signals? What exact receptors are required to exist on a sensory neuron in order for that neuron to transmit pins and needles/parasthesia signals? Thanks again! – smeeb Dec 17 '14 at 19:58
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    This is still an active field of research, and not being a specialist in the field I cannot say what this specific signal is. It is possible that this signal has not yet been discovered by science. – March Ho Dec 17 '14 at 20:00
  • That makes sense and +1 @March Ho for the excellent help thus far. Just out of curosity, what field or specialty would be actively researching this topic? Biomedicine? Bioelectricity? – smeeb Dec 17 '14 at 20:05