Neurons are one of two main groups of cells in the brain: neurons and glia. Neurons and glia differ in structure and in function, but both are absolutely essential to the work of the brain.
Functions of neurons
Neurons pass along information. When you look at the text on this page, your eyes send electrical impulses to brain neurons. An impulse received by one neuron is passed onto the next and the next in a kind of electrical bucket brigade, which is interpreted by the brain as words. A simple message, like that of the knee jerk reflex, may be carried by only two neurons. But most messages require from thousands to millions of neurons working together to convey the information.
Functions of glia
Glia, also called glial cells, are support cells. Each neuron in your brain has 10 to 50 glial cells helping to care for it. Since you were born with 100 billion neurons (roughly the same as the number of stars in the galaxy), that means you have one to five trillion glial cells.
These cells surround neurons, offering physical and nutritional support. They surround synapses and play a (recently-discovered) role in enhancing synaptic transmission. They encase neuronal axons, speeding the transmission of information within the neuron. And they form the blood-brain-barrier, which can protect the brain by denying blood-borne pathogens access to it.
Every aspect of a neuron’s structure is designed to optimize its ability to transmit information. Most neuronal cell bodies are round or roughly triangular in appearance. Fine, threadlike processes stretch out from these cell bodies. Multiple processes called dendrites receive information coming into the neuron. The information, then flows through the cell body and down the transmitting arm of the neuron, called an axon. Most neurons have many dendrites for receiving information and only one axon for transmitting information.
[Random thought: Does this mean we should listen more than we talk?]
The axon passes information along to the dendrites of the next cell (or cells) in line. Neurons are built to last a lifetime, and in the healthy brain, they continue to grow by making additional connections throughout life.
The flow of information in the brain is dependent upon billions of interconnected neurons. Normally many neurons carry the same bit of information simultaneously. That duplication insures that loss of a few neurons will not disrupt the flow of information. However, a continuing loss of neurons, such as occurs over time in many neurodegenerative disorders, will eventually overwhelm the brain’s fail-safe systems and interrupt the flow of information.
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