I am an electronic engineer so I am thinking about this from an electronics outlook.

How does the addressing system work, As I see it, the nervous system is small parallel branches attached to larger "serial" lines (spinal cord).

The serial line is then attached to the brain, but how does it then figure out where the message came from and then get the message back to the place it came from.

If I were to build a robot I would have an addressing system with each message and maybe some kind of error checking to make sure the messages don't become corrupted, but as it's not an electronic system I don't see how the brain could possibly do this. unless it is a fully parallel system and there is a single wire going from every sensor back to the CPU..


2 Answers 2


The brain knows where a sensory signal came from by what neuron is doing the signalling. The incoming neuron is dedicated to signals from one source and, since it is not shared by other sources, does not need to have an encoding as to what the source was. When your toe touches something, the sensation causes a pulse which, amazingly, travels along a single nerve cell (neuron) up to the brain stem. That neuron has its nucleus at a dorsal root ganglion located by the spinal cord, and has a fiber (axon) that extends to the source (toe) and another extending up to the brain stem. This pathway is called the PCML pathway and the Wikipedia article has some readable details. This page has a schematic and tabular summary, while this site has a good descriptive overview.

If a robot were built along the same sort of design, to determine what was happening at 1000 places in its body, it would have 1000 wires running to its central computer. You probably wouldn't choose to use such a design, but then you probably wouldn't be designing a robot that has to build itself from raw materials.

  • $\begingroup$ That is exactly the answer I was looking for, thank you so much. So it is literally a fully parallel system. So extending what I said below, does every sensation reach the brain or are some so, meaningless that they don't need much processing. E.g. Hair, stuff like that. Beacuase if so does that mean there's millions of axons and neurons $\endgroup$
    – Shasam
    Feb 20, 2014 at 22:44
  • $\begingroup$ If you perceive a sensation, it had a path; the signaling is indeed massively parallel. Some sensations are processed in the periphery and a derived signal sent on to the brain; The density also varies (the hands have many nerves, the back, few). There is also peripheral processing like the knee reflex. Also there are nerves that have little or no flow to the brain; see autonomic nervous system. If this answer is what you wanted, you can accept it by clicking the checkmark to the left. $\endgroup$
    – mgkrebbs
    Feb 21, 2014 at 0:03
  • 1
    $\begingroup$ Is it precisely 1-to-1? The number of somatosensory neurons < axons in spinal cord to brain? I don't think this is absolutely true, but not sure. For example on your back, you have a very coarse sensation, but there's no missing area of sensation. To save bandwidth, it is plausible that there were some converging signals in the spinal cord level. $\endgroup$
    – Memming
    Feb 21, 2014 at 19:52
  • $\begingroup$ Isn't this simply a circular reasoning? The essential question must be: How does the brain know 'which neuron is doing the signalling'? The answer must be of meta-sensation, something like self-recognition. Though I think no one in the world can really answer it.. $\endgroup$
    – le4m
    May 13, 2017 at 3:13

your question is a little bit difficult to answer in the current forum format, however I'd suggest you reading about Reflex arc - from this you can understand consequence of the events in simple reflex on the level of spinal cord (i.e. monosinaptic pathway) and very complex reflexes managed by multiple neural cells (neurons).

A classic example of the reflex -

enter image description here

If you want to dive into the very complex explanations you should read some textbook and probably not forums.

Probably, you'd like to know what the potential of action is....

  • $\begingroup$ Thanks for the answer but as I see it these are all just connections and how the conduction works, but somehow the tip of my little toe can send a variety of messages to the brain and it knows exactly which toe and which sensation, there must be some kind of addressing. Biology is so complex $\endgroup$
    – Shasam
    Feb 20, 2014 at 21:11
  • 1
    $\begingroup$ I have just noticed this similar post biology.stackexchange.com/questions/550/… where the top comment says the way the brain distinguishes is largely unknown. $\endgroup$
    – Shasam
    Feb 20, 2014 at 21:19
  • $\begingroup$ the messages come from specific receptors and along any pathway there are interconnections for different regions. Your question is complex, so we cannot answer before you'll be more specific... $\endgroup$
    – Ilan
    Feb 20, 2014 at 21:21
  • $\begingroup$ Well okay a specific sensation, is the brain processing the movement of hairs and does it know the location of every single hair. Well obviously it does because if you touch it lightly I know exactly where I was touched.. Or do you mean something else by specifics? $\endgroup$
    – Shasam
    Feb 20, 2014 at 21:29
  • $\begingroup$ considering hairs you're a little bit wrong - the brain join skin regions in quadrants and each quadrant has about 1cm sides, thus you cannot differentiate 2 touches inside the same quadrant $\endgroup$
    – Ilan
    Feb 20, 2014 at 21:33

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