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Neurons

 

THE BASICS


Neurons are the building blocks of the brain. Your every perception, thought, and behavior can be traced back to them. At their most basic level, neurons are just cells. They have "cell bodies," which contain a single nucleus and other typical cellular "guts." But unlike other cells in the body, neurons are built for communication. Projecting from one end of the cell is a long tentacle called an axon. Its main purpose is to transmit messages to other neurons, like a telephone cable. The other end of a neuron has branches like a tree; these are dendrites, and they receive messages from the axons of other neurons.

All neurons share these basic properties, but otherwise there's a wide variety of cells in our bodies. Sensory neurons detect pressure and temperature, and send signals about those sensations, as well as pain, back to the brain-the electrochemical equivalent of "Yes, that mug is still way too hot to pick up."

Motor neurons, on the other hand, bring the brain's messages to the muscles, instructing those in your arm, for instance, to put the mug down right away.

Finally, there are interneurons, which mediate between sensory and motor neurons, as well as communicating among themselves. All of the neurons in the brain are, in fact, interneurons. Even these vary widely in form. Some have one or two dendrites; others have a thousand.

ON THE FRONTIER


Brain researchers are currently studying how neurons grow. Studies have now revealed the substances that help axons lengthen and the way new dendrites sprout from brain cells. Eventually, this research will not only show how neurons develop in the fetal and infant brain, but also help treat disorders like Alzheimer's, in which neurons become diseased or damaged. In fact, researchers have already designed synthetic substances that encourage new brain cells to form.

COCKTAIL PARTY TIDBITS

  • No one knows for sure how many neurons there are in a human brain. (Would you want to count them?) But many experts put the number at about one hundred billion. If you spread out the cell membranes of all those neurons, you'd cover four soccer fields. (Yes, that would make it hard to play.)
  • The longest axons in the human body-the ones that stretch from the spinal cord all the way to our toes-can be three or four feet long. In giraffes, those same axons are about fifteen feet long.
  • Neurons are inconceivably tiny. On average, tens of thousands of them can fit on the head of a pin.
 
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