The function of neurons in the brain is to process internal and external input received by the human body and ensure that the body continues to function properly. Individual neurons do not perform this function on their own, but the collective of neurons working together in the brain handles all stimuli coming from inside and outside the body. Each neuron is an electrically excitable cell that passes information to other neurons through chemical and electrical signals, and the combined signals of neuron groups in the brain allow carefully processed responses to input.
When transferring signals between each other, the neurons in the brain rely on both chemical and electrical data. Chemical signals are transmitted between neurons by way of neurotransmitters, which are small molecules that drift from one neuron to another to continue a pathway. Electrical signals transmit data through the neurons themselves, traveling from their origin in receivers called dendrites until they reach the end of the neuron, where chemical signaling must take over. Many human disorders, some treatable and others debilitating, are the result of errors in electrical or chemical signal transmission among neurons in the brain.
All neurons in the brain are structurally similar, although different regions of the brain may have slightly different neuronal structures. The different structures give specific groups of neurons particular capabilities, which is why different areas of the brain are specialized for different tasks. For example, the visual cortex handles input from the eyes, and the motor cortex handles movement. Every area of the brain is specialized for something, and the different areas of the brain often work together in routine tasks. There is a common misconception in popular culture that humans only use a small fraction of their brains, but this is actually not true; the entire brain is consistently put to use on a daily basis.
Science has shown that the neurons in the brain are far more adaptable than was previously believed. For many years, it was believed that if any damage occurred to the brain that the function of those affected neurons would be permanently and irreversibly lost. A multitude of more recent studies has shown that the brain displays the ability to reroute functions though alternative neural pathways, known as plasticity. Some people with damage to the visual centers of the brain can still see, and some people with half of their brains missing can function relatively normally.