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How many neurons fire in an eye blink?

  1. May 29, 2016 #1
    I am wondering how many neurons would need to fire approximately in a human brain in order for the eye to blink, or for example, for a head to nod?

    And I am referring directly to just the motor act, not all the internal brain processes that might lead to an eye blink. And I am not necessarily including the peripheral neurons that need to get to the eye lid, although, that approximation would be a nice bonus thing to know too.

    Here is my crude guess, does it make sense to think this way?
    The brain has 100 billion neurons, and the motor cortical homunculus would be perhaps up to 5% of the total brain, which would be about 5 billion neurons. And in that region, the eye lids (or neck muscles) would yet again be perhaps 5% of that area, which would give about 250 million neurons in that area. Could it be that this many neurons would be involved in this action? Even if I took a fraction of that, that is still a whole a lot of neurons.

    Any thoughts super appreciated! :)
  2. jcsd
  3. May 30, 2016 #2


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    Have you done any research on this?
  4. May 30, 2016 #3

    Fervent Freyja

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    The mechanisms responsible for the eye blinking mostly take place outside of the brain (other than the obvious), blinking uses the Orbicularis oculi muscles which is attached to facial motor neurons (to trigeminal nerve and ganglion, spinal trigeminal tract and nucleus and so on). That is not inside the brain, but also connects to the spinal cord. Blinking is a natural motor reflex.

    No your crude guess does not make sense at all.

  5. May 30, 2016 #4
    Thanks for your response Fervent Freyja.

    I guess using an eye blink might have been the wrong example since it actually is a reflex. Would the act of winking at someone involve the brain's motor cortex area?

    Still, regardless of whether an action goes through the brain or not, I am curious about the estimation of the number of actual neurons that are involved in simple movements like these. That is why I used the example of a head nod too. That is not a reflex and it is a simple movement.

    Sounds like my guesses as to what nerve areas are involved in eye blink were incorrect but it would be still good to know what the estimate is for the # of neurons for the neural circuits that are involved in an act like this.

    I was reading this document when I thought about the number of neurons that would be involved in an action. It would be a voluntary action if this part of the brain is involved?
    http://www.brainfacts.org/~/media/Brainfacts/Article Multimedia/Educator Section/Olson Handout.ashx

    Or maybe making an approximation of this sort is not something that is possible to do yet?

    Thanks again.
    Last edited: May 30, 2016
  6. May 30, 2016 #5


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    Nature. 2004 Feb 19;427(6976):704-10.
    Whisker movements evoked by stimulation of single pyramidal cells in rat motor cortex.
    Brecht M, Schneider M, Sakmann B, Margrie TW.

    It depends on the brain region and the movement. Brecht and colleagues were able to elicit whisker movements by stimulating a single neuron in the motor cortex.
  7. May 30, 2016 #6
    I see, so it is totally varied. That is incredible that a single neuron can move a whisker!
    Thanks @atyy!
  8. Jun 2, 2016 #7

    Fervent Freyja

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    The old-fashioned way of making an approximate neuron count is to dissect the location that you are interested in with a knife, slice that into very thin sections, place under a microscope, and then start counting (with a grid)! But, it wouldn't be as easy in this case. The cranial nerve can be counted as one neuron (I think it's funny to tell people that they are getting on my neurons to be more technically correct... ), then you will need to follow the process further up from the brain-stem to the mid-brain and locate the Edinger-Westphal nucleus and do another count, then continue until you find other areas possibly responsible for winking your eye. The approximation won't be of how many neurons are actually involved in any one movement, most neurons in those areas will go unused. Instead, you may gain an approximation for the potential number of neurons that could be involved in the action in only an isolated area that could be involved. You won't be able to get a true count for the action, but you can make some deductions to get a certain minimum count that could be potentially involved in the process. Anyway, how do you suppose a person is winking with no stirring motive? If you see something pleasant then all sorts of areas your the brain are likely to start firing with all the physiological changes taking place when lusting! :wink: I suggest that you break your question down into many problems to solve, it could at least give you a better question to ask. The neuron count will likely vary depending on the cause of the winking.

    To find the pathways that are taken would need an advanced imaging technique, even then, mapping cannot give an approximation of the number of neurons firing in the action. At least I don't know so, and even if we could distinguish each active neuron during the winking, not all neurons may be used in the exact same process again, and all brains are incredibly unique in their neural framework. You may probe for the specific neuron responsible for some actions like atyy posted, but that won't show the pathways involved that cause the whisker to twitch on different natural occasions. Was it itchy? Smelling for food? Was the rat growling too? My Husband can be seen twitching and convulsing sometimes, the rat could have far more neurons involved in the process of twitching his whiskers if throwing a tantrum. :DD

    We still have much more to discover about the brain, and even with our technology we haven't been able to determine the areas responsible for many functions in fine detail. Recently in rats, it was found that the brain has a lymphatic system. The lymphatic system in the body circulates fluid primarily by body movements that occur naturally throughout our day (does not rely on muscles surrounding the vessel for circulation). And we see that swelling occurs during periods of immobility. Then, if the brain also has a lymphatic system that has to rely on the same mechanisms for circulation, and has the same branching, vessel patterns- then a bedridden patient is getting little circulation and you would think that the brain would swell as well.
  9. Jun 2, 2016 #8

    jim mcnamara

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  10. Jun 2, 2016 #9
    Thanks Fervent Freyja that was really helpful!
    The point about how many neurons are potentially fired is great.

    Even though there is no easy way of figuring out or approximate the numbers of neurons, I understand that the way to approach it is to figure out the areas involved (and by the way, I am aware that there are whole systems that cause the eye blink, I was just aiming to keep things simple/isolated) and even if there was a way to guess the approximate # of neurons in each of the areas, not necessarily all the neurons fire. That's a great insight.

    It's a complex question for sure. I guess we're looking at any number between 1 neuron and millions of them, depending on the event. :)
  11. Jun 20, 2016 #10
    Just had a question that I couldn't quite be sure if the article in the link addresses.

    Even though the movement of a rat whisker is caused by one neuron in the motor region, that doesn't mean that there are not more than that one neuron involved in this instinctual reflex. What I mean is, one neuron can't get an external stimuli, internal "processing" and then finally motor movement. This would still be different parts of the brain in charge of each of these functions. And that this was just one motor neuron in the motor region moving one whicker. Or is it possible that this same neuron could also collect sensory data?

    After all, it did get stimulated by Brecht and colleagues. I'm guessing that a similar stimulus to Brecht's would usually come from some other neuron or neurons in the nervous system, rather than directly from the outside, like they were manage to pull off in this experiment.
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