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The overall number of synapses in the human brain is roughly 1,000 trillion, i.e. 10,000 synapses per neuron.

My question here is three-fold:

  1. I assume that each structural type of neuron (basket, pyramidal, ...) has a somehow characteristic average number of in-coming and out-going synaptic connections, i.e. not every type of neuron will have about 10,000 in-coming and 10,000 out-going synaptic connections. I am looking for a thorough overview of these characteristic numbers by structural type.

  2. I assume that for some functional groups of neurons (see The human brain in numbers I: neurons) there are characteristic average numbers of in-coming and out-going synaptic connections per neuron. I am looking for a thorough overview of these characteristic numbers by functional group.

  3. Finally, for some functional groups there are presumably characteristic ratios of inner and outer synaptic connections: "x % of the in-coming synaptic connections of a neuron in group X come from other neurons in this group, the rest comes from the outside. y % of the out-going synaptic connections of a neuron in group X go to other neurons in this group, the rest goes to the outside". I am looking for a thorough overview of these characteristic ratios by functional group.

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closed as too broad by David, Bryan Krause, canadianer, another 'Homo sapien', AliceD Jul 24 '17 at 20:03

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Woah, that's just too broad a question! Divide it into (at least) three questions, lest even a bounty of +500 points is not very likely to get you a complete answer for such a big question... $\endgroup$ – another 'Homo sapien' Jul 23 '17 at 10:32
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    $\begingroup$ Yes, incredibly incredibly too broad. You might look into projects like the Blue Brain Project in Europe and the BRAIN initiative in the US. $\endgroup$ – Bryan Krause Jul 23 '17 at 17:29
  • $\begingroup$ I'd like to, but these are real huge projects with vast web sites. And I am not sure if I would find thorough and concise overviews of the kind I'm looking for. So if anyone knows... $\endgroup$ – Hans-Peter Stricker Jul 23 '17 at 18:45
  • $\begingroup$ @hansstricker honestly, if you ain't sure you'd get all that you want even on such vast websites, how do you expect somebody here to pack all of it in a little answer? $\endgroup$ – another 'Homo sapien' Jul 24 '17 at 11:41
  • $\begingroup$ The little answer might be a link that would be hard to find. $\endgroup$ – Hans-Peter Stricker Jul 24 '17 at 12:09