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Most recently updated on April 10, 2013
Like all living tissue, the brain and spinal cord are made up of cells, which in turn have characteristics and names unique to their function. The cells unique to the central nervous system are neurons and neuroglia.
Neurons are the workhorses of the nervous system, sending and receiving signals to and from the brain via interconnections too numerous and complex for scientists to count or map. “Hundreds of billions” of neurons in the brain, with many times more interconnections, is as precise a figure as they can currently estimate. Each nerve cell is made up of a nerve body, with branches called dendrites and axons extending outward like a starburst (see Figure 1). These extensions are responsible for transferring signals between cells. The axon is a single extension from the body that typically carries signals from the neuron to other neurons or organs such as the heart, muscles, and lungs. The dendrites, usually found in large numbers on each neuron, commonly serve the purpose of receiving signals from other neurons or sensory organs. Together these form a complex network of “wires” that carry nerve messages in pulsed signals to affect every human action, including thought, sensation, motor movement, respiration, and laughter.
Unlike many other cells in the body, neurons cannot be replaced once they die. Although this remains largely true (most dead neurons cannot be replaced), new experiments in animals have been able to regenerate limited neurons in limited areas. Thus, it’s fair to assume that each person has a fixed number of neurons since birth. Nevertheless, the brain possess an amazing ability called plasticity—which means that it can often adjust to injury or loss of brain cells by making new interconnections, which take over for the loss of others. Younger children, whose brains are still developing, seem to have the greatest ability to recuperate from this sort of damage. But scientists have found, since the 1990s, that even adult brains have enough flexibility to form some new connections in the brain. As you accumulate medical information about your child’s situation, please keep this remarkable ability in mind.
Neuroglia are the second type of cell found in the brain. The literal meaning, a “nerve glue,” describes their supportive role. During fetal and infant development, certain neuroglial cells help guide the neurons to their final destinations in the brain and spinal cord. Others became scaffolding for the neurons, surrounding and nourishing them and ingesting debris. There are many more neuroglial cells than neurons in the brain, and neuroglia are involved in over half of all brain tumors.
Tumors arising from neuroglial or glial cells are referred to generally as gliomas but will often take their more specific names from the type of glial cell involved. The most common pediatric brain tumors involving glial cells are cerebellar and hemispheric astrocytomas, brainstem gliomas, optic pathway gliomas, ependymomas, and gangliogliomas.
Brain tumors in children arising from neurons or their precursors include primitive neuroectodermal tumors (PNETs), such as medulloblastomas and pineoblastomas.
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