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Where Did the First Neuron Come From?

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How can a body of trillions of cells act as one, and where did the first nerve cell come from? This video follows one chain of causes: single cells already had electrical spikes and chemical signals, cells stayed together, diffusion became too slow, and spikes, synapses and muscle were assembled from old parts into nerve nets and brains. Dates are ranges from molecular clocks and fossils, and open questions are marked as such. Sources: Hodgkin & Huxley 1952; Alegado et al. 2012; Sakarya et al. 2007; Burkhardt et al. 2011 and 2023; Senatore et al. 2017; Keijzer et al. 2013; Dupre & Yuste 2017; Arendt et al. 2016; Schultz et al. 2023; Evans et al. 2020; Ma et al. 2012 (full list in references.md). Draft: check the facts before publishing. Made with Eureka, a Nebulytic product.

The question

How did a body made of thousands of cells learn to act as one animal, and where did the first nerve cell come from, when neurons look so unlike anything a single cell does? It matters because every thought, reflex and heartbeat runs on neurons, yet the earliest animals had none. The surprise is that the parts were not new. Single cells already had the electrical and chemical hardware, and the first neurons repurposed it. ---

Chapters

  • 0:00Hook: how can trillions of cells act as one?
  • 0:44One cell can already decide
  • 1:40Cells that stay together
  • 2:30Why chemical signals are too slow
  • 3:19A signal that does not fade
  • 4:20The neuron and the synapse
  • 5:24Nerve and muscle evolved together
  • 6:32From nerve net to brain
  • 7:30Assembled, not invented

Sources

  1. Retrieved only as search summaries or abstracts unless noted; check each before publishing. "To be verified by author" marks items not confirmed.
  2. Alegado RA et al. (2012). A bacterial sulfonolipid triggers multicellular development in the closest living relatives of animals. eLife 1:e00013.
  3. Arendt D, Tosches MA, Marlow H (2016). From nerve net to nerve ring, nerve cord and brain: evolution of the nervous system. Nature Reviews Neuroscience 17:61-72.
  4. Burkhardt P et al. (2011). Primordial neurosecretory apparatus identified in the choanoflagellate *Monosiga brevicollis*. PNAS (title and authors to be verified by author).
  5. Burkhardt P et al. (2023). Syncytial nerve net in a ctenophore adds insights on the evolution of nervous systems. Science 380:293-297 (to be verified by author).
  6. Dupre C, Yuste R (2017). Non-overlapping neural networks in *Hydra vulgaris*. Current Biology 27:1085-1097.
  7. Eckert R (1972). Bioelectric control of ciliary activity. Science 176:473-481 (to be verified by author; original not retrieved).
  8. Elices I et al. (2023). An electrophysiological and kinematic model of *Paramecium*, the "swimming neuron". PLoS Computational Biology.
  9. Erwin DH (2015). Early metazoan life: divergence, environment and ecology (review of the origin of animals, about 750-800 Mya; to be verified by author), and Dating early animal evolution using phylogenomic data (2017, authors to be verified).
  10. Evans SD et al. (2020). *Ikaria wariootia*, a bilaterian from the Ediacaran of South Australia. PNAS (title and details to be verified by author).
  11. Gehling JG et al. (2014). Scratch traces of large Ediacara bilaterian animals. Journal of Paleontology 88.
  12. Hodgkin AL, Huxley AF (1952). A quantitative description of membrane current and its application to conduction and excitation in nerve. Journal of Physiology 117:500-544.
  13. Jékely G, Keijzer F, Godfrey-Smith P (2015). An option space for early neural evolution. Philosophical Transactions of the Royal Society B (not retrieved; to be verified by author).
  14. Katz B, and colleagues. Quantal release of transmitter and its dependence on calcium (del Castillo & Katz 1954; Katz & Miledi 1967; to be verified by author).
  15. Keijzer F, van Duijn M, Lyon P (2013). What nervous systems do: early evolution, input-output, and the skin brain thesis. Adaptive Behavior 21:67-85.
  16. Liebeskind BJ, Hillis DM, Zakon HH (2011). Evolution of sodium channels predates the origin of nervous systems in animals. PNAS (to be verified by author).
  17. Ludeman DA, Leys SP et al. (2014). Evolutionary origins of sensation in metazoans: functional evidence for a new sensory organ in sponges. BMC Evolutionary Biology (to be verified by author).
  18. Ma X, Hou X, Edgecombe GD, Strausfeld NJ (2012). Complex brain and optic lobes in an early Cambrian arthropod. Nature 490:258-261.
  19. Mackie GO, Passano LM (1968). Epithelial conduction in hydromedusae. Journal of General Physiology (to be verified by author).
  20. Moran Y, Barzilai MG, Liebeskind BJ, Zakon HH (2012-2015). Evolution of voltage-gated ion channels at the emergence of Metazoa (to be verified by author).
  21. Moroz LL et al. (2014). The ctenophore genome and the evolutionary origins of neural systems. Nature 510:109-114.
  22. Sakarya O et al. (2007). A post-synaptic scaffold at the origin of the animal kingdom. PLoS ONE 2:e506.
  23. Schultz DT et al. (2023). Ancient gene linkages support ctenophores as sister to other animals. Nature 618:110-117.
  24. Senatore A, Reese TS, Smith CL (2017). Neuropeptidergic integration of behavior in *Trichoplax adhaerens*. Journal of Experimental Biology 220:3381-3390.
  25. Steinmetz PRH et al. (2012). Independent evolution of striated muscles in cnidarians and bilaterians. Nature 487:231-234.
  26. Nerve-free *Hydra*: JoVE protocol "Generation and long-term maintenance of nerve-free Hydra" and the review "On being a Hydra with, and without, a nervous system: what do neurons add?" (authors to be verified by author).
  27. Images: platform asset library, "made for videos" sprites m-805412c121 (choanoflagellate), m-7617373a25 (*Hydra*), m-d9c57ab9d8 (early bilaterian worm); schematic illustrations, licence per platform library terms (to be verified by author).
  28. Burkhardt P et al. (2011). Primordial neurosecretory apparatus identified in the choanoflagellate *Monosiga brevicollis*. PNAS 108:15264–15269. https://pmc.ncbi.nlm.nih.gov/articles/PMC3174607/
  29. Ogura A, Takahashi K. (1976). Artificial deciliation causes loss of backward swimming response in *Paramecium*. Nature 264:170–172. https://www.nature.com/articles/264170a0.pdf
  30. Alegado RA et al. (2012). A bacterial sulfonolipid triggers multicellular development in the closest living relatives of animals. eLife 1:e00013. https://elifesciences.org/articles/00013
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