Decoded: What Are Neurons? – Scientific American

Neurons are the tiny processing units within the human brain and nervous system.

Our brains have about 86 billion neurons. Even more are spread throughout the body, communicating by electrical and chemical signals through incredibly thin cables.

Whenever we see, hear, or otherwise perceive the world, thousands of sensory neurons send signals to our spinal cord and brain. And thanks to other neurons, we’re able to make sense of those perceptions and react accordingly.

Scientists have been studying the brain for millennia. In fact, the oldest known scientific document is a 4,000-year-old anatomical report on traumatic brain injuries.

But the brain is an extremely difficult organ to study. Even if you manage to get a brain sample under a microscope, you basically just see a tangled web of cells.

In 1873, Italian physician Camillo Golgi found a way to stain brain slices, to show the tissue in far more detail than ever before. Using his technique, a Spanish researcher named Santiago Ramón ee ca-HAL discovered that even though the cells were connected, they were still individual structures. Which became known as neurons.

By breaking down the nervous system into its smallest components, Cajal set the foundation for the next century of neuroscience. He and Golgi split the Nobel Prize in 1906.

Because neurons are miniscule pieces in a giant system, their power lies in their ability to communicate with other neurons. This happens over small gaps called synapses. When neurons communicate frequently, the synapses between them get stronger, making it easier to send future signals. 

This happens all the time, all across the brain. And it explains how we learn and form memories: we literally rewire our brains through our experiences. We refer to the brain’s fundamental ability to change as “neuroplasticity.”

Humans have most of our neurons from birth. Neurons start out as stem cells, before moving to different brain regions where they assume specific roles. Early in our development, the brain prunes away excess neurons and their connections, leaving the ones that remain stronger. Those that remain become part of our sense of smell, others our ability to walk or perform other motor skills.

Unlike other cells in the body, which regenerate at intervals and then die, most neurons last a lifetime

At least, ideally. People lose neurons in brain regions they stop using. For instance, if you never left your home again, you’d likely lose neurons in the brain region involved in spatial navigation. 

Neuron death can lead to loss of basic brain functions and motor skills. That’s what happens in degenerative diseases like Alzheimer’s and Parkinson’s disease, where neurons stop functioning properly and die off. There’s some evidence that these diseases result from protein clumps clogging the brain, but scientists are still working to figure out exactly how this happens.

That may be essential for finding effective treatments, which have remained largely elusive.

Neurological changes aren’t necessarily permanent. In addition to the brain’s general neuroplasticity, there’s solid evidence that even adults are able to form new neurons, through a process called “neurogenesis.” 

Researchers are still studying the extent to which neurogenesis happens in adults. But they think it may be important for healthy brain functioning.

And because neurons communicate through electrical signals, we can directly alter brain circuits with electrical stimulation. Scientists have found ways to stimulate the brain and spinal cord to restore function to paralyzed muscles and relieve chronic pain.

Private companies are also trying to jump on the hype, claiming their brain stimulation products can improve memory and accelerate skill acquisition. But researchers are still trying to figure out which effects are real and which are a placebo. And since zapping your own brain could pose serious health risks, it may be best, for now, to train your neurons the old-fashioned way.

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