The human brain. It’s spongy to the touch, weighs about three pounds and looks kind of like a head of cauliflower
Some parts of the brain, including the cerebellum and brain stem, are quite primitive. They help us coordinate our movements and control basic survival functions like breathing.
And then there’s the cerebrum—the biggest and most evolved part of the brain. It controls the body’s conscious experiences and voluntary movements. It allows us to feel, think and create. And to receive, store and retrieve memories. In short, it makes us human.
Imagine you have a brain in your hand and slice it down the middle. What you’re left with are the two hemispheres of the cerebral cortex. Each of the hemispheres contains four lobes: the frontal, temporal, parietal and occipital lobes. These lobes are specialized to do certain things. For example, the frontal lobe specializes in decision making, while the occipital lobe specializes in vision. In addition to the lobes, there are deeper structures in the brain like the limbic system, which is important to long-term memory. (You can roll your mouse over the picture of the brain above to find out more about the parts of the brain.)
Every part of the brain—and the rest of the nervous system, for that matter—contain neurons (more than 100 billion of them in all). Neurons are nerve cells with some very special properties. Each one has dendrites that gather information transmitted from other cells, and an axon that transmits information to other cells. The average neuron communicates with between 1000 and 10,000 other cells.
Neurons don’t touch when they communicate. Instead, they secrete chemical molecules called neurotransmitters that ferry nerve impulses across the tiny gaps, or synapses, to other neurons. How many neurotransmitters are secreted is important. If many are secreted, the message travels very strongly. If few are secreted, the message is weak.
The information that your neurons transmit comes from many sources. Let’s use a finger touch as an example. When you touch something with your finger, nerve impulses immediately “fire” from your finger, to your brain. These impulses travel from one neuron to the next astonishingly quickly. Once in the brain, the information contained in these impulses is deciphered, with the result that you can identify what you touched.
Here’s a simple example
Say you touch something without looking at it. Your brain will check: Was what you touched cold? hot? wet? soft? hard? slick? rough? and so on. These answers will enable it to compare features of what you touched with things you have touched in the past: water, skin, glue, metal, sand, bananas, tree bark, whatever. It will use these comparisons to determine what it most likely touched.
What if it’s something you’ve never touched before? Let’s use a snake as an example. Your brain might “save” your “first touch” of a snake to use as a point of comparison for future touches. It does so by transferring the information to your memory. (Memory is a subject unto itself. Find out more about memory.) So the next time you touch something, “snake” will be on the list of things your brain compares to.
The importance of our neural network and the information it conveys to us cannot be overstated. These impulses contain the information that we need to make sense of the world around us—to figure out what is what, what goes with what, and much, much more. When this system breaks down, the result can be that we begin to lose ourselves, as in schizophrenics and Alzheimer’s patients. (Learn more about how brain plasticity science has proven the brain can change for better or worse.)
More numerous—but less glamorous—than neurons are the brain’s glial cells, also called glia. About 90% of the cells in the brain are glial cells. (There are probably more than one trillion of them in the average human brain!) Glial cells might be thought of as servants to the neurons—they make myelin to protect neurons and speed transmission, dispose of dead neurons, provide nutrition for neurons, repair injured neurons, and support neurons in many other ways. About the only thing they don’t do is ferry impulses around.
These parts of the brain work together to perform every function that make our lives our own—they enable us to speak our native language, play the guitar, dance the cha-cha, love our families, remember our childhood, and much, much more.
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