More about neurons

I want to make a point here that we know less about the brain than is generally acknowledged. Our picture of the functioning of a neuron is taken as more or less settled knowledge; only small refinements are likely. But the refinements that are regularly published are not small. Now we have a paper (citation below) that is extraordinary.

Bywalez and others have shown that the little spines on the dendrite trees of neurons can themselves act as miniature neurons accomplishing computations similar to a full neuron (at least in the olfactory bulb part of the brain and probably other parts too) and that some synapses can be two sided, transmitting signals in both directions. This allows dendrite to dendrite communication. In effect the neck of the spine can isolate the spine from the rest of the neuron, allowing it to reach an action potential level of voltage in its area without interference from the rest of the dendrite tree, and so it is able to send a signal backwards out of the spine.

classic neuron

classic neuron

We are used to thinking of neurons as, in effect, huge add-gates that take a multitude of synapses giving inputs of various strengths and those inputs are combined in the dendrites into a voltage level in the main cell body. If that voltage is above a threshold, an action potential voltage, a signal, is propagated down the neuron’s axon to the dendrites other, usually distant, neurons. There it influences how those other neurons act by contributing a positive or negative voltage to the receiving dendrites’ totals. It is fairly easy to imagine how this works and to mimic it with electronic circuits.

But neuroscience keeps finding exceptions to this theory. There are glial cells assisting and interfering with the process and they can communicate with each other by a different mechanism. There are signals that bypass the whole dendrite calculation and input their signal at the cell body root of the axon, thereby over-riding other inputs. There are axon to axon synapses. Neurons can multitask by calculating and then sending two separate message codes to two separate groups of receiving neurons. Signals can go backwards up the axon. Some neurons can learn timing delays in their signaling. And now this: action potentials can be generated in the little spines of the dendrites and some synapses are not one way transmitters with pre and post halves, but can work both ways. The standard model is getting tattered with exceptions. No doubt there are many more exceptions to come. I venture that we are nowhere near understanding neurons and neuron network behavior.

Bywalez, W., Patirniche, D., Rupprecht, V., Stemmler, M., Herz, A., Pálfi, D., Rózsa, B., & Egger, V. (2015). Local Postsynaptic Voltage-Gated Sodium Channel Activation in Dendritic Spines of Olfactory Bulb Granule Cells Neuron DOI: 10.1016/j.neuron.2014.12.051

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6 thoughts on “More about neurons

  1. jeanni gerwin

    Wow, to know that the brain is more complicated then one was lead to believe. Imagine, a complex organ that continues to become more complex with advancements in science and the continued ability to study at increasingly microscopic levels. Yes, I do imagine that you are correct. There are more things unknown about the brain than are known. We continue to evolve as a species every day. Our science evolves also. We may never completely understand the workings of the entire organ we call our brain, but with continued research and new discoveries as the ones you pointed out, we will increase our knowledge and understanding of its workings and capabilities.

  2. michelle harner

    I find our ignorance to scientific topics to be widespread. I believe yes we have come a long way in what we know and the technologies we can use to help discover more but like you state about the neurons we are always finding exceptions or add-ons to what we know. When I first began to learn about neurons back in high school the idea seamed simple; it’s how our body “communicates” nerve impulses. And then the complexity steps up and you realize neurons are like fingerprints… no two are the same. And when I think about how many dendrites a neuron can have and that the more neurons mean the more communications, the possibilities seem endless. Unfortunately I find it impossible for us to ever truly find what every neuron is capable of, not just because of their complexity but because we are constantly evolving and that means our neurons are evolving and changing as well.

  3. Sonja Fernandez

    It’s an interesting concept considering there are such a large amount of spines on each dendrite tree. Each dendrite spine was thought to provide a substrate for memory storage and synaptic transmission, and also serve to increase the number of possible contacts between neurons. It’s hard to imagine each small piece doing so much more than they already do. Now the question is do they still take all the imputs from the other neurons as if that is their only task or is it a mix of their own plus other neurons excitatory inputs?


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