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might as well use it!
    Let’s look at this process in more detail. Neurons pass information down their axons by
    generating small electrical signals that last a thousandth of a second. These signals are called
    “spikes” because they represent sudden increases in the electrical currents in a neuron (see graph).
    Spikes—known to brain geeks as action potentials—look the same whether they come from squid,
    rats, or Uncle Fred, making them a huge success story in the evolutionary history of animals. Racing
    down axons at speeds up to several hundred feet per second, spikes bring signals from your brain to
    your hand fast enough to escape the bite of a dog or the heat of a frying pan. They help all animals get
    away from imminent danger—fast.

    Spikes conclude their business when they arrive at the axon’s end. At that point, neurons assume
    their other identity, as chemical signaling machines. Each neuron in the brain receives chemical
    signals from some neurons and sends chemical signals to others. Communication between neurons
    relies on chemicals called neurotransmitters, which are released from small areas at the end of the
    axon when triggered by the arrival of a spike. Every neuron makes and receives up to several hundred
    thousand chemical connections, called synapses, with other neurons. Neurotransmitters stick to
    synaptic receptors on the dendrites or cell bodies of another neuron, triggering further electrical and
    chemical signals. All these steps, from release to detection, can take place in a thousandth of a
    second.
    Synapses are the essential components of communication in your brain. Your thought patterns,
    basic abilities and functions, and individuality are determined by how strong these synapses are, how
    many of them you have, and where they are. Just as connections in computers mostly connect internal
    components of the computer with one another, neurons mostly use synapses to talk to each other
    within the brain. Only a small fraction of axons form their synapses outside the brain or spinal cord,
    sending signals to other organs of the body, including the muscles.
    In addition to being fast, synapses are also very small. The dendritic tree of a typical neuron is
    about two-tenths of a millimeter wide. Yet it receives up to two hundred thousand synaptic inputs
    from other neurons. Indeed, a cubic millimeter of your brain contains as many as a billion synapses.
    Individual synapses are so small that they contain barely enough machinery to function and are
    unreliable, so that arriving spikes often fail to cause any release of neurotransmitter at all.
    Did you know? Loewi’s dream of the neurotransmitter
    Back in 1921, it wasn’t clear how neurons, or even cells in general, talked with one
    another. German scientist Otto Loewi made a key observation when he studied how the
    heart receives signals to speed up or slow down. He was convinced that the vagus nerve, a
    long nerve that comes from the brainstem and attaches to the heart, secreted a substance to
    slow the heartbeat. In his laboratory, he carefully dissected the hearts of frogs with the
    vagus nerve attached. When he stimulated the vagus nerve with electric shocks, the heart
    slowed down. How did this happen? Loewi’s hypothesis was that something came out of
    the nerve to cause this effect, but he didn’t know how to test this idea with an experiment.
    Stuck, he did what many people do: he slept on it. One night he woke up, struck with an
    insight on how to do the experiment. Satisfied, he went back to sleep. The next morning …
    nothing. He couldn’t recall what experiment to do. The next time he had the dream, he took
    care to write down his idea. Unfortunately, the next morning he couldn’t read his own
    writing. Luckily, he had the dream again. This time he didn’t wait: he got up, went to the
    laboratory, and did the experiment that would win him the Nobel Prize in Physiology or
    Medicine in 1936.
    The experiment was a simple