Our brain contains 100 billion neurons (nerve cells). Our gray matter. Each neuron has an axon – a little arm – that transmits information in the form of electrical impulses to the dendrites – receivers – of nearby neurons. Dendrites branch twig-like from each neuron. Between axon and dendrite, the synapse is the point of connection. Axons commune with dendrites across the synaptic gap.
When neurons “fire,” they emit a rat-a-tat-tat of electrical pulses that travel down the axon and arrive at its terminal endings, which secrete from tiny pockets a neurotransmitter (dopamine, say, or serotonin). The neurotransmitter ferries the message across the synaptic abyss and binds to the synapse, whereupon the synapse converts it back into an electrical pulse ...
What blows my mind is this: A single neuron can make between 1,000 and 10,000 connections. At this moment our neurons are making, it could be, a million billion connections.
What this electrical/chemical transaction gives us is culture: nail polish, Poland, comic books. Otis Redding belting out “Try a Little Tenderness” at the 1967 Monterey International Pop Music Festival, along with its memory, its YouTube reenactment, its recordings and coverings and remixings, its moment in history.
The geography of the brain ought to be taught in school, like the countries of the world. The deeply folded cortex forms the outer layer. There are the twin hemispheres, right brain and left brain. (We may be of two minds.) There are the four lobes: frontal in front, occipital (visual cortex) in back, parietal (motor cortex) on top, and temporal behind the ears. There’s the limbic system (seat of emotion and memory) at the center. There’s the brain stem, whose structures keep us awake (required for consciousness) or put us to sleep (required for regeneration of neurotransmitters).
The brain also has glial cells, white matter. Glial cells surround and support neurons, carry nutrients to neurons and eat dead neurons. Some glial cells regulate transmission and pulverize post-transmission neurotransmitters. Others produce myelin, which surrounds and protects axons. Glial cells are no longer thought to be mere glue. When stimulated, they make, not electricity as neurons do, but waves of calcium atoms. They also produce neurotransmitters – glutamate (excitatory) and adenosine (inhibitory). We may not know what they are up to, but we know they’re up to something.
So there you have the brain: a three-pound bagful of neurons, electrical pulses, chemical messengers, glial cells. There, too, you have the biological basis of the mind. “Anything can happen,” says the poet C. D. Wright, “in the strange cities of the mind.” And whatever does happen – any thought, mood, song, perception, delusion – is provided to us by this throbbing sack of cells and cerebral substances.
But what, then, is consciousness?
Priscilla Long, “Our Mind-Boggling Brain,” from The American Scholar, Winter 2010