Physiology & Anatomy Codexery

Brain

Central organ of the nervous system in vertebrates and most invertebrates.

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The brain is a complex organ composed primarily of neurons and glial cells, with the human cerebral cortex containing approximately 14–16 billion neurons and the cerebellum an estimated 55–70 billion neurons.[1][2] Neurons communicate via specialized junctions called synapses, and the human brain has been estimated to contain approximately 100 trillion synapses.[3][4] Modern neuroscience treats the brain as a biological computer that acquires, stores, and processes information from the surrounding world.[5]

Key facts and history

Glial cells perform critical functions including structural support, metabolic support, insulation, and guidance of development.[2] Neurons send signals to specific target cells via axons, which are thin protoplasmic fibers that extend from the cell body.[3] Some neurons emit action potentials constantly at rates of 10–100 per second, while others are quiet most of the time.[6] The first vertebrates appeared over 500 million years ago during the Cambrian period.[7]

All vertebrate brains share a common underlying form that appears most clearly during early embryonic development.[3] The brain develops from three vesicular swellings at the front of the neural tube, which become the forebrain, midbrain, and hindbrain.[3] Electrochemical pulses called action potentials, lasting under a thousandth of a second, are the signals transmitted by axons, and these travel at rates between 1 and 100 meters per second.[8] In mammals, the forebrain is significantly larger, and the pallium develops into the neocortex, a structure with six layers.[9][10]

A near-complete diagram of the C. elegans connectome was published by scientists in 1986, which subsequently enabled research that would have been impossible without it.[11][12]

What the research sources say

A 2012 Scientific American article notes that the human brain contains around 86 billion neurons and 100 trillion synapses.[12] The same source reports that some neuroscientists think creating a connectome for the entire human brain is not the best use of limited resources.[12] Without connectome maps, scientists cannot thoroughly understand how the brain processes information at the level of the circuit.[12] The article quotes researcher Cornelia Bargmann stating that scientists do know a great deal about how the C. elegans brain works.[12]

Neglected neurons shrivel in the developing brain and new neurons sprout to replace them, while adult neurons change connection strength daily for learning and memory.[12]

References

  1. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Saladin, "Human anatomy", McGraw-Hill, 2011, p. 416; von Bartheld, "The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting.", The Journal of Comparative Neurology, 15 December 2016, p. 3865–3895 (we also read that source) en.wikipedia.org
  2. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Kandel, "Principles of neural science", McGraw-Hill, 2000; Saladin, "Human anatomy", McGraw-Hill, 2011, p. 416; von Bartheld, "The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting.", The Journal of Comparative Neurology, 15 December 2016, p. 3865–3895 (we also read that source) en.wikipedia.org
  3. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Kandel, "Principles of neural science", McGraw-Hill, 2000 (original not read by us) en.wikipedia.org
  4. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Williams, "The control of neuron number", Annual Review of Neuroscience, 1988, p. 423–453; Heisenberg, "Mushroom body memoir: from maps to models", Nature Reviews Neuroscience, 2003, p. 266–275; Shepherd, "The Synaptic Organization of the Brain", Oxford University Press US, 2004 (original not read by us) en.wikipedia.org
  5. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Yuste, "The new century of the brain", Scientific American, March 2014, p. 38–45 (original not read by us) en.wikipedia.org
  6. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Barnett, "The action potential", Practical Neurology, 2007, p. 192–197 (original not read by us) en.wikipedia.org
  7. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Shu, "Head and backbone of the Early Cambrian vertebrate Haikouichthys", Nature, 2003, p. 526–529 (original not read by us) en.wikipedia.org
  8. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Douglas, "Neuronal circuits of the neocortex", Annual Review of Neuroscience, 2004, p. 419–451 (original not read by us) en.wikipedia.org
  9. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Barton, "Mosaic evolution of brain structure in mammals", Nature, 2000, p. 1055–1058 (original not read by us) en.wikipedia.org
  10. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Aboitiz, "The evolutionary origin of the mammalian isocortex: Towards an integrated developmental and functional approach", Behavioral and Brain Sciences, 2003, p. 535–552; Barton, "Mosaic evolution of brain structure in mammals", Nature, 2000, p. 1055–1058 (original not read by us) en.wikipedia.org
  11. Wikipedia, "Brain" (CC BY-SA 4.0), which cites: Jabr, "The Connectome Debate: Is Mapping the Mind of a Worm Worth It?", Scientific American, 2012-10-02; Hodgkin, "Encyclopedia of Genetics", Elsevier, 2001, p. 251–256; Berg, "Sexual dimorphism in the complete connectome of the Drosophila male central nervous system", 2025, p. 2025–10; Bates, "Distributed control circuits across a brain-and-cord connectome", Nature, 2026, p. 2025.07.31.667571 (we also read that source) en.wikipedia.org
  12. Jabr, "The Connectome Debate: Is Mapping the Mind of a Worm Worth It?", Scientific American, 2012-10-02. facts only, no text reused. scientificamerican.com

Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Brain (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.

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Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.

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