Hierarchical Brain

An explanation of the human brain

First published 1st February 2024. This is version 1.5 published 2nd March 2024.
Three pages are not yet published: sleep, memory and an index.
Copyright © 2024 Email info@hierarchicalbrain.com

Warning - the conclusions of this website may be disturbing for some people without a stable mental disposition or with a religious conviction.


Neurons, and the connections between them called synapses, are the building blocks for the workings of the brain and the obvious components for the lowest level in my proposed hierarchy of levels of description of the workings of the human brain.

This page is a high-level description of the characteristics and capabilities of a neuron, but, like all living cells, a neuron is an incredibly complex piece of machinery that can be described at many levels of detail. A lower level of detail on the workings of both neurons and synapses depends upon the movement of ions.

Despite the potential for complex decision making in the many different types, sizes and shapes of neurons and their synapse connections, there is a basic functionality that they all provide that can be described as coincidence detection. This is the basis of my proposed hierarchical structure that describes the working of the brain.

Contents of this page
Functionality - an overview of the functionality of a neuron, including coincidence detection.
Physical characteristics - an overview of the physical characteristics of a neuron.
Statistics - some numbers, sizes and distances about neurons.
External connections and support - the connections between neurons, and the support provided by glial cells.
Change over time - the changes that can take place in neurons that cause changes to signals.
Signals - the nature of the signals created and passed on by neurons.
Concluding remarks - how the functionality of a neuron is used in the next higher level of the hierarchy, and some other concluding remarks.
References - references and footnotes.


Physical characteristics


External connections and support

Change over time


Concluding remarks

References For information on references, see structure of this website - references

  1. ^ New Scientist article The amazing ways electricity in your body shapes you and your health - Sally Adee 22nd February 2023
    Around the heading “Electric signalling” : “We have long known that a neuron’s ability to relay messages hinges on electricity - specifically, a set-up that ensures different ions stay on different sides of nerve cell membranes. Neurons like to keep potassium ions inside and sodium ions outside. Both types of ion are positively charged, but, due to the vagaries of ion concentration gradients and head-exploding equations, the upshot is that the inside of a neuron is around 70 millivolts more negatively charged than the outside. This is called its resting potential. Although the resting potential is minuscule - around one-tenth the voltage that activates a transistor in the microchip that runs your phone - it is vital to the functioning of nerve cells.”
  2. ^ Know your neurons - article published by Scientific American magazine 2012
    “Scientists have classified neurons into four main groups based on differences in shape. ... Researchers also categorize neurons by function. ... Neurons differ from one another structurally, functionally and genetically, as well as in how they form connections with other cells. ... So how many different types of neurons have scientists named so far? ...the answer is at least in the hundreds.”
    There are many different ways of categorising the different types: for example, see this list of different types, 302 different types listed at SciCrunch (the database takes over 20 seconds to load, and you then need to click the “children” tab), and many thousands at Neuromorpho.org by cell type.
  3. ^ The human brain in numbers - a linearly scaled-up primate brain - Herculano-Houzel 2009
    doi: 10.3389/neuro.09.031.2009 downloadable here or see GoogleScholar.
    See table, top of page 7, which says that the total number of neurons in the human brain is 86 billion.
  4. ^ How many neurons do you have? Some dogmas of quantitative neuroscience under revision - Lent, Azevedo, Andrade-Moraes and Pinto 2011
    doi: 10.1111/j.1460-9568.2011.07923.x downloadable here or see GoogleScholar.
    See seven lines from end of page 4: “...absolute counts yielded an average of 86 billion neurons in male human brains...”
  5. ^ The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting - von Bartheld, Bahney and Herculano-Houzel 2016
    doi: 10.1002/cne.24040 downloadable here or see GoogleScholar.
    This paper is a good summary of the history of counting the number of cells in the human brain and the different ways that have been used to count them.
  6. ^ An estimation of the number of cells in the human body - Bianconi, Piovesan, Facchin, Beraudi, Casadei, Frabetti, Vitale, Pelleri, Tassani, Piva, Perez-Amodio, Strippoli and Canaider - 2013
    doi: 10.3109/03014460.2013.807878 downloadable here or see GoogleScholar.
    Near end of abstract on page 1: “Results: A current estimation of human total cell number calculated for a variety of organs and cell types is presented. These partial data correspond to a total number of 3.72 x 1013.”
  7. ^ In Search of Memory - Kandel 2006 Norton & Company USA - see GoogleScholar.
    This very readable book by the Nobel prize winner is an autobiography, history and text book all in one.
    In chapter 2, page 65:
    “Some neurons in the brain have as many as forty dendritic branches.”
  8. ^ Ibid. In Search of Memory
    In chapter 5, page 77: “The form of the signal and its role in encoding information were addressed in the second phase, which began in the 1920s with Edgar Douglas Adrian’s work. Adrian developed methods of recording and amplifying the action potentials propagated along the axons of individual sensory neurons on the skin, thereby making the elementary utterances of nerve cells intelligible for the first time. In the process, he made several remarkable discoveries about the action potential and how it leads to what we perceive as a sensation. To record action potentials, Adrian used a thin piece of metal wire. He placed one end of the wire on the outside surface of the axon of a sensory neuron on the skin and then ran the wire to both an ink writer (so he could look at the shape and pattern made by the action potentials) and a loudspeaker (so he could hear them). Every time Adrian touched the skin, one or more action potentials were generated. Each time an action potential was generated, he heard a brief bang! bang! bang! over the loudspeaker and saw a brief electrical pulse on the ink writer. The action potential in the sensory neuron lasted only about 1/1000 of a second and had two components: a swift upstroke to a peak, followed by an almost equally rapid downstroke that returned it to the starting point.”
  9. ^ ^ Ibid. In Search of Memory
    In chapter 5, page 77: “The ink writer and the loudspeaker both told Adrian the same remarkable story: all of the action potentials generated by a single nerve cell are pretty much the same. They are about the same shape and amplitude, regardless of the strength, duration, or location of the stimulus that elicits them. The action potential is thus a constant, all-or-none signal: once the threshold for generating the signal is reached, it is almost always the same, never smaller or larger. The current produced by the action potential is sufficient to excite adjacent regions of the axon, thus causing the action potential to be propagated without failure or flagging along the whole length of the axon at speeds of up to 100 feet per second, pretty much as Helmholtz had earlier found!”
  10. ^ Dendrite structure - Fiala, Spacek and Harris 1999
    in book Dendrites ed. Stuart, Spruston and Hausser pub. Oxford University Press 2017,
    article downloadable here or see GoogleScholar.
    Page 2, second paragraph: “Dendrites are rarely longer than 1-2 mm, even in the largest neurons, and are often much smaller.”
    The table on page 3 quotes statistics for the “Principal cell of globus pallidus (human)”. Unfortunately, the globus pallidus has particularly large and strange-shaped neurons and very unusual dendritic arborisations, so this may not be a typical example.
  11. ^ Cognitive Neuroscience: The Biology of the Mind - Gazzaniga, Ivry and Mangun, Fourth Edition 2014 Norton & Company USA
    A comprehensive text book edited by Michael Gazzaniga, Richard Ivry and George Mangun.
    Page 31, second column. Under the heading “The Action Potential”, having described the refractory period when the neuron’s internal voltage has not yet returned to its normal equilibrium potential, it says:
    “The refractory period lasts only a couple of milliseconds and has two consequences. One is that the neuron’s speed for generating action potentials is limited to about 200 action potentials per second.”
  12. ^ ^ Ibid. Cognitive Neuroscience: The Biology of the Mind
    Page 32, first column: “Action potentials are always the same amplitude; therefore, they are said to be ‘all or none’ phenomena. Since one action potential is the same amplitude as any other, the strength of the action potential does not communicate anything about the strength of the stimulus. The intensity of a stimulus (e.g., a sensory signal) is communicated by the rate of firing of the action potentials: more intense stimuli elicit higher action potential firing rates.”
  13. ^ Reorganization and plastic changes of the human brain associated with skill learning and expertise - Chang 2014
    doi: 10.3389/fnhum.2014.00035 downloadable here or see GoogleScholar.
    Start of introduction on page one: “Neuroplasticity, which refers to the brain’s ability to change its structure and function, is not an occasional state of the brain, but rather the normal ongoing state of the human brain throughout the life span. Plastic changes in the human brain lead to brain reorganization that might be demonstrable at the level of behavior, anatomy, and function and down to the cellular and even molecular levels.”
  14. ^ Stable neuron numbers from cradle to grave - Nowakowski 2006
    doi: 10.1073/pnas.0605605103 downloadable here or see GoogleScholar.
    First page, top of second column: “In humans, only the dentate gyrus population contributes new neurons.” - the dentate gyrus is part of the hippocampus.
  15. ^ Human Hippocampal Neurogenesis Persists throughout Aging - Boldrini, Fulmore, Tartt, Simeon, Pavlova, Poposka, Rosoklija, Stankov, Arango, Dwork, Hen and Mann 2018
    doi: 10.1016/j.stem.2018.03.015 downloadable here or see GoogleScholar.
    End of Introduction, page 591, third paragraph “Healthy elderly people have the potential to remain cognitively and emotionally more intact than commonly believed, due to the persistence of AHN into the eighth decade of life.” - AHN is Adult Hippocampal Neurogenesis, i.e. the growth of new neurons in the hippocampus.
  16. ^ National Geographic article The bigger brains of London taxi drivers (anon) - 29th May 2013
    Navigation-related structural change in the hippocampi of taxi drivers - Maguire, Gadian, Johnsrude, Good, Ashburner, Frackowiak and Frith 2000
    doi: 10.1073/pnas.070039597 downloadable here or see GoogleScholar.
    Second sentence of abstract: “The posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects. A more anterior hippocampal region was larger in control subjects than in taxi drivers. Hippocampal volume correlated with the amount of time spent as a taxi driver”
  17. ^ A review of cell assemblies - Huyck and Passmore 2013
    doi: 10.1007/s00422-013-0555-5 downloadable here or see GoogleScholar.
    Last two lines of page 4: “The basic structure of the brain is a loosely coupled net of neurons where neurons are firing constantly at a low rate.”
    and beginning of fourth paragraph, page 14: “Neurons are firing constantly...”
  18. ^ Response to the Edge.org question What do you consider the most interesting recent [scientific] news? What makes it important? - Lisa Feldman Barrett 2015
    First paragraph: “For many years, scientists believed that your neurons spend most of their time dormant and wake up only when stimulated by some sight or sound in the world. Now we know that all your neurons are firing constantly, stimulating one another at various rates. This intrinsic brain activity is one of the great recent discoveries in neuroscience.”
  19. ^ Why Neurons Have Thousands of Synapses, a Theory of Sequence Memory in Neocortex - Hawkins and Ahmad 2016
    doi: 10.3389/fncir.2016.00023 downloadable here or see GoogleScholar.
    From abstract on page 1: “Pyramidal neurons represent the majority of excitatory neurons in the neocortex. Each pyramidal neuron receives input from thousands of excitatory synapses that are segregated onto dendritic branches. The dendrites themselves are segregated into apical, basal, and proximal integration zones, which have different properties. ... First we show that a neuron with several thousand synapses segregated on active dendrites can recognize hundreds of independent patterns of cellular activity even in the presence of large amounts of noise and pattern variation. We then propose a neuron model where patterns detected on proximal dendrites lead to action potentials, defining the classic receptive field of the neuron, and patterns detected on basal and apical dendrites act as predictions by slightly depolarizing the neuron without generating an action potential. By this mechanism, a neuron can predict its activation in hundreds of independent contexts.”

Page last uploaded Wed Jan 31 07:25:03 2024 MST