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In each neuron. . . . An RNA molecule made up of merely 25 links could have any one of a million billion different combinations, . . . In fact, every RNA molecule contains many hundreds of units—not merely 25.
Isaac Asimov

A neuron is an electrically excitable cell that processes and transmits information through electrical and chemical signals. These signals between neurons occur via synapses, specialized connections with other cells. Neurons can connect to each other to form neural networks. Neurons are the core components of the brain and spinal cord of the central nervous system (CNS), and of the ganglia of the peripheral nervous system (PNS).


  • A healthy, mature human being of normal intelligence may have upwards of 20 million RNA molecules [thought to serve as a ‘filing system’ for memory] in each neuron. . . . An RNA molecule made up of merely 25 links could have any one of a million billion different combinations, . . . In fact, every RNA molecule contains many hundreds of units—not merely 25.
    • Isaac Asimov, New York Times Magazine, October 9, 1966 as cited in Awake! magazine, in the article: Designed to Last Forever, 10/8 1970.

Asimov adds:

  • There is no question, then, that RNA presents a filing system perfectly capable of handling any load of learning and memory which the human being is likely to put upon it—and a billion times more than that quantity, too.
  • When you learn a new skill ... you are training your neurons to connect in a new way. . . . The more you use your brain, the more efficient it will become.
    • Drs. R. and B. Bruun, The Human Body.
  • A typical neuron makes about ten thousand connections to neighboring neurons. Given the billions of neurons, this means there are as many connections in a single cubic centimeter of brain tissue as there are stars in the Milky Way galaxy.
  • An illustration I use to get people to understand it is this: I'll ask major corporate audiences: Why don't you just take all your traditional beliefs about organizations, and apply them to the neurons in your brain?
  • Life and consciousness are the two great mysteries. Actually, their substrates are the inanimate. And how do you get from neurons shooting around in the brain to the thought that pops up in your head and mine? There's something deeply mysterious about that. And if you're not struck by the mystery, I think you haven't thought about it.
  • When you read a book, the neurons in your brain fire overtime, deciding what the characters are wearing, how they're standing, and what it feels like the first time they kiss. No one shows you. The words make suggestions. Your brain paints the pictures.
  • Neurons do not just fire and not fire . . . they must be capable of passing on much more subtle information than yes or no. They are not just hammers hitting the next nail, either more frequently or less so. They are, to complete this analogy, a carpenter’s kit, with screwdrivers, pliers, pincers, mallets—and hammers. . . . Each neural impulse is transformed along the way, and nowhere else than at the synapses.
    • Anthony Smith, The Mind.
    • Note: The chemical synapse has a further advantage. It takes less space than an electrical synapse, which explains why the human brain has so many synapses. The journal Science gives a figure of 100,000,000,000,000—equivalent to the number of stars in hundreds of Milky Way galaxies.
  • Every neuron, ... contains about a million pumps—each one is a slight bump on the cell membrane—and every pump can swap about 200 sodium ions for 130 potassium ions every second.
    • Anthony Smith, The Mind.
  • In some developing tissues, a mass of identical cells somehow differentiates into many types. ...The mechanism behind this process appears to have evolved early on, and is highly conserved... At first this intimate mixture of fates seems puzzling, but there is a relatively easy way to achieve it: instruct each cell 'Be different from your neighbors.' This mechanism is known as lateral inhibition. An example is the nervous system. Since nerve cells form networks with long thin connections, and their ability to function depends on this geometry... when a cell develops into a nerve cell, it sends signals to nearby cells telling them not to do the same.
  • We are what we are, ... because our brains are basically chemical machines rather than electrical ones.
    • Richard Thompson, The Brain.
  • Octopuses have hundreds of suckers, each one equipped with its own ganglion with thousands of neurons. These 'mini-brains' are interconnected, making for a widely distributed nervous system. That is why a severed octopus arm may crawl on its own and even pick up food.

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