The Birth, Life, and Death of a Neuron

Birth majority of neurons present in brains by birth Extent new neurons generated in brain controversial to neuroscientists New evidence to support neurogenesis, birth of new neuronal cells, is a lifelong process

Birth Neurons are born in areas of the brain that are rich in concentrations of neural precursor cells (also called neural stem cells). These cells have the potential to generate most, if not all, of the different types of neurons and glia (supporter cells) found in the brain.

Birth Neural stem cells increase by dividing in two and producing either two new stem cells, or two early progenitor cells, or one of each. When a stem cell divides to produce another stem cell, it is said to self- renew. This new cell has the potential to make more stem cells.

Birth- Differentiation When a stem cell divides to produce an early progenitor cell, it is said to differentiate. Differentiation means that the new cell is more specialized in form and function. An early progenitor cell does not have the potential of a stem cell to make many different types of cells. It can only make cells in its particular lineage.

Life- Migration Neurons travel to the place in the brain where it will do its work. Some neurons migrate by following the long fibers of cells called radial glia. Neurons glide along the fibers until they reach their destination. Neurons also travel by using chemical signals. These chemical signals guide the neuron to its final location.

Life- Migration Not all neurons are successful in their journey. Scientists think that only a third reach their destination. The rest either never differentiate, or die and disappear along their migration. Some neurons survive the trip, but end up where they shouldnt be. Mutations in the genes that control migration create areas of misplaced or oddly formed neurons that can cause disorders such as childhood epilepsy or mental retardation. Some researchers suspect that schizophrenia and the learning disorder dyslexia are partly the result of misguided neurons.

Life- Migration

Death Some diseases of the brain are the result of the unnatural deaths of neurons. In Parkinsons disease, neurons that produce the neurotransmitter dopamine die off in the basal ganglia, an area of the brain that controls body movements. The brain can no longer control the body and people shake and jerk in spasms.

Death In Huntingtons disease, a genetic mutation causes over-production of a neurotransmitter called glutamate, which kills neurons in the basal ganglia. As a result, people twist and writhe uncontrollably (big choreographed movements.)

Death In Alzheimers disease, unusual proteins (tau proteins-cant see them on an MRI, but will see the brain shrinking. Can only see with autopsy) build up in and around neurons in the neocortex and hippocampus, parts of the brain that control memory. When these neurons die, people lose their capacity to remember and their ability to do everyday tasks.

Death Blows to the brain, or the damage caused by a stroke, can kill neurons outright or slowly starve them of the oxygen and nutrients they need to survive. (can only survive minutes without oxygen, where as muscle cells can go hours.) Spinal cord injury can disrupt communication between the brain and muscles when neurons lose their connection to axons located below the site of injury. These neurons may still live, but they lose their ability to communicate.

Death- Neurotransmitter Overload

Death- Being Attacked

Stem Cells- What? Stem cells are primitive cells that give rise to other types of cells. Totipotent cells, a type of stem cell, are considered the "master" cells of the body because they contain all the genetic information needed to create all the cells of the body plus the placenta, which nourishes the human embryo. At the end of the long chain of cell divisions that make up the embryo are terminally differentiated cells.

Stem Cells- Where? Scientists already get these cells from human embryosbut many people oppose this and the federal government has banned most research. It was recently discovered that some stem cells also occur in the bodies of adults, rather than exclusively in embryos. Scientists think that embryonic stem cells have a much greater utility and potential than the adult stem cells, because embryonic stem cells may develop into virtually every type of cell in the human body.

Stem Cells- Who? In the mid 1800s, scientists began to recognize that cells were the basic building blocks of life, and that cells gave rise to other cells. In the early 1900s, European scientists realized that all blood cells came from one particular "stem cell." In 1998, researchers at the University of Wisconsin led by James Thomson isolated and grew stem cells from human embryos.

Stem Cell- How? Embryos Umbilical Cords (Clip and Save) Extraction from adults (blood marrow, brain, etc.) Because of the controversy of the extraction of stem cells from unborn fetuses, scientist search for new sources everyday.

Stem Cell- Why? A study has proven that embryonic stem cells provide a unique therapy that has the potential to reduce the morbidity and mortality of heart disease. Researchers at Stanford University School of Medicine report the first success using stem cells to populate the damaged region with new neurons in rats. If those cells also replace the function of the lost cells, they could help people recover after a stroke.

Stem Cells- Why A man in his mid-50s had been diagnosed with Parkinson's at age 49. The disease grew progressively, leading to tremors and rigidity in the patient's right arm. Traditional drug therapy did not help. Stem cells were harvested from the patient's brain using a routine brain biopsy procedure. They were cultured and expanded to several million cells. About 20 percent of these matured into dopamine-secreting neurons. In March 1999, the cells were injected into the patient's brain. Three months after the procedure, the man's motor skills had improved by 37 percent and there was an increase in dopamine production of 55.6 percent. One year after the procedure, the patient's overall Unified Parkinson's Disease Rating Scale had improved by 83 percent this at a time when he was not taking any other Parkinson's medication!