NEURONS AT WORK [ CONNECTIONS / ACTION / GROWTH & SUPPORT / PLASTICITY ]
Neurons serve different functions. Motor neurons carry impulses to activate glands and muscles. Sensory neurons send impulses from the skin and other body parts to the central nervous system. Interneurons, residing in the brain and spinal cord, integrate the signals and are crucial in making decisions. Thus, neurons allow for information from the body to reach the brain, be processed, and sometimes result in responses.
Some liken the neuron to an old- fashioned, landline telephone. The body of the neuron compares to the body of the phone, where sig- nals are processed. The telephone receiver compares to the dendrites and their ability to gather informa- tion. And the axon compares to a telephone line, sending informa- tion processed in the phone body along an electrically conductive wire. It has the potential to pass information along to any other phone on the planet.
IF NEURONAL CIRCUITRY rewires itself in response to stimulation, do the brains of teens raised on the Internet and high-tech gadgets differ from those of older genera- tions? The answer most likely is yes. UCLA psychiatrist Gary Small believes tech-savvy children strengthen synaptic connections for electronic communica- tion while their circuitry for a face-to-face world, such as reading body language, fades. Meanwhile, late adopters of technology lag in their ability to master new communication media.
The human brain contains ill the neighborhood of 100 billion neurons. Each neuron reaches out toward others with an array of dendrites and axon terminals. Each is capable of communicating with any other and, in the process, forging thousands of synaptic connections through the thickets of dendrites and axon terminals. All told, the brain has hundreds of trillions of synapses. No computer can match the human brain for its complexity and its potential for creative thought.
Communication occurs where two neurons come together. Camillo Golgi, a contemporary of Ramon y Cajal’s, believed that neurons physically touched each other, forming a continuous net- work of neural fibers. Ramon y Cajal disagreed. In his sketches, he painstakingly drew neurons whose dendrites invariably terminated at a tiny gap that prevented them from touching other neurons. His drawings did not lie.
In the synaptic cleft, a neuron communicates with its neighbors by issuing electrochemical commands that may be strictly localized or extend the length of the longest chains ofaxons.
Neurons are not physically bound to each other like so many lengths of pipe, so they have the flexibility to make, break, and remake relationships with other neurons. The ability to reshape neural interac- tions in the brain is referred to as plasticity. The brain’s ability to rewire itself helps it stay sharp.
The number of synapses may be as high as one thousand trillion, or the number 1 followed by 15 zeroes.
As the brain ages, it loses individual neurons, but it retains its power to form new connections that increase the mind’s complexity. In short, if new educational experiences challenge the brain to form new synaptic connections, its neurons will do more with less.
Experimental data with labora- tory animals demonstrate the principle of “use it or lose it.” When lab animals are placed in an environ- ment with challenging toys, their brains develop a far greater number of neuronal connections than those raised in a dull environment. The brains of animals from stimulating environments will even weigh more because of the greater number of synapses.
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