Transcript Birth, Life, & Death of a Neuron

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 selfrenew.
• 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
•
•
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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 shouldn’t 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 Parkinson’s 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 Huntington’s 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 Alzheimer’s disease, unusual proteins
(tau proteins-can’t 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
embryos—but 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!