An adult stem cell is an undifferentiated cell found among differentiated cells in a tissue or organ, can renew itself, and can differentiate to yield the major specialized cell types of the tissue or organ. The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found. Some scientists now use the term somatic stem cell instead of adult stem cell. Unlike embryonic stem cells, which are defined by their origin (the inner cell mass of the blastocyst), the origin of adult stem cells in mature tissues is unknown.
It was not until the 1990s that scientists agreed that the adult brain does contain stem cells that are able to generate the brain's three major cell types—astrocytes and oligodendrocytes, which are non-neuronal cells, and neurons, or nerve cells.
The adult tissues reported to contain stem cells include brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin and liver.
NIH Stem Cell Basics, s4
Scientists know less about the functions of glial cells than they do about the functions of neurons. Glial cells fulfill a variety of functions including
- Glial cells function as supporting elements in the nervous system to provide structure and to separate and insulate groups of neurons.
- Oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system form myelin, the sheath that wraps around certain axons.
- Some glial cells are scavengers that remove debris after injury or neuronal death.
- Some glial cells buffer the potassium ion (K+) concentration in the extracellular space, and some glial cells take up and remove chemical neurotransmitters from the extracellular space after synaptic transmission.
- Some glial cells guide the migration of neurons and direct the outgrowth of axons during development.
- Some glial cells induce formation of impermeable tight junctions in endothelial cells that line the capillaries and venules of the brain to form the blood-brain barrier.
- Glial cells may serve nutritive functions for nerve cells.3
NIH Teacher's Guide on Addiction which has good neuro-info.
The brain produces new cells to repair the damage from multiple sclerosis (MS) for years after symptoms of the disorder appear, according to a recent study. However, in most cases the cells are unable to complete the repairs. These findings suggest that an unknown factor limits the repair process and may lead to new ways of treating this disorder.
"The brain is making a serious attempt to repair the damage," says Bruce D. Trapp, Ph.D., of the Cleveland Clinic Foundation in Ohio, who led the study.
The new oligodendrocytes extended "arms" that produced myelin-related proteins and grew around the damaged axons as if they were trying to repair the myelin. However, in most cases the axons were not repaired.
One of the central questions in MS research is how to promote myelin repair. Many researchers have concentrated on increasing the number of oligodendrocytes through stem cell transplantation or other means. However, this study suggests that problems with the axons or with the tissue that surrounds them may prevent remyelination. Many of the axons that were not remyelinated looked abnormal, whereas remyelinated axons appeared healthy. This suggests that therapies which prevent axon degeneration or help oligodendrocytes complete the repair process in other ways may be necessary.
NIH news article on MS Repair - from 2002