Nerve cells, or neurons, generally do not multiply in the same way other cells in the body do. Mature, fully differentiated neurons are typically incapable of cell division. However, new neurons can be generated through a process called neurogenesis.
Neurogenesis: The Creation of New Neurons
Neurogenesis involves the creation of new neurons from neural stem cells and progenitor cells. This process is primarily observed in specific regions of the brain.
Neural Stem Cells and Progenitor Cells
- Neural Stem Cells: These are self-renewing cells capable of differentiating into various types of brain cells, including neurons, astrocytes, and oligodendrocytes.
- Progenitor Cells: These are cells derived from neural stem cells that are more restricted in their differentiation potential and divide to produce neurons or glial cells.
Where Does Neurogenesis Occur?
Neurogenesis primarily occurs in two main regions of the adult mammalian brain:
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Subventricular Zone (SVZ): Located lining the lateral ventricles, the SVZ is a major neurogenic niche that produces new neurons that migrate to the olfactory bulb.
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Dentate Gyrus of the Hippocampus: This region is involved in learning and memory. New neurons generated here are incorporated into existing neural circuits and contribute to hippocampal function.
Steps in Neurogenesis:
- Proliferation: Neural stem cells divide, either symmetrically (producing more stem cells) or asymmetrically (producing one stem cell and one progenitor cell).
- Differentiation: Progenitor cells differentiate into immature neurons.
- Migration: Newly formed neurons migrate to their final destination in the brain.
- Integration: The new neurons integrate into existing neural circuits, forming synapses and becoming functional.
Neurogenesis vs. Neuronal Division
It's important to distinguish neurogenesis from typical cell division (mitosis) observed in other cell types. While neurogenesis results in the creation of new neurons from stem and progenitor cells, mature neurons themselves do not divide to create more copies of themselves. Instead, neurogenesis utilizes stem and progenitor cells to expand the neuronal population.
