No wonder we have a hell of a time getting competently rehabbed. We don't even know yet what types of brain cells we have or what they do. I wonder where the 65 billion number came from, it used to be assumed that we had 100 billion until someone a couple of years ago determined there was no basis for it and came up with 80 billion.
http://www.alphagalileo.org/ViewItem.aspx?ItemId=149839&CultureCode=en
Using a process known as single cell sequencing, scientists at
Karolinska Institutet have produced a detailed map of cortical cell
types and the genes active within them. The study, which is published in
the journal Science, marks the first time this method of analysis has
been used on such a large scale on such complex tissue. The team studied
over three thousand cells, one at a time, and even managed to identify a
number of hitherto unknown types.
“If you compare the brain to a fruit salad, you could say that
previous methods were like running the fruit through a blender and
seeing what colour juice you got from different parts of the brain,”
says Sten Linnarsson, senior researcher at the Department of Medical
Biochemistry and Biophysics. “But in recent years we’ve developed much
more sensitive methods of analysis that allow us to see which genes are
active in individual cells. This is like taking pieces of the fruit
salad, examining them one by one and then sorting them into piles to see
how many different kinds of fruit it contains, what they’re made up of
and how they interrelate.”
The knowledge that all living organisms are built up of cells is
almost 200 years old. Since the discovery was made by a group of 19th
century German scientists, we have also learnt that the nature of a
particular body tissue is determined by its constituent cells, which
are, in turn, determined by which genes are active in their DNA.
However, little is still known about how this happens in detail,
especially as regards the brain, the body’s most complex organ.
In the present study, the scientists used large-scale single-cell
analysis to answer some of these questions. By studying over three
thousand cells from the cerebral cortex in mice, one at a time and in
detail, and comparing which of the 20,000 genes were active in each one,
they were able to sort the cells into virtual piles. They identified 47
different kinds of cell, including a large proportion of specialised
neurons, some blood vessel cells and glial cells, which take care of
waste products, protect against infection and supply nerve cells with
nutrients.
With the help of this detailed map, the scientists were able to
identify hitherto unknown cell types, including a nerve cell in the most
superficial cortical layer, and six different types of oligodendrocyte,
which are cells that form the electrically insulating myelin sheath
around the nerve cells. The new knowledge the project has generated can
shed more light on diseases that affect the myelin, such as multiple
sclerosis (MS).
“We could also confirm previous findings, such as that the pyramidal
cells of the cerebral cortex are functionally organised in layers,”
says Jens Hjerling-Leffler, who co-led the study with Dr Linnarsson.
“But above all, we have created a much more detailed map of the cells of
the brain that describes each cell type in detail and shows which genes
are active in it. This gives science a new tool for studying these cell
types in disease models and helps us to understand better how brain
cell respond to disease and injury.”
There are estimated to be 100 million cells in a mouse brain, and 65
billion in a human brain. Nerve cells are approximately 20 micrometres
in diameter, glial cells about 10 micrometres. A micrometre is
equivalent to a thousandth of a millimetre.
The study was carried out by Sten Linnarsson’s and Jens
Hjerling-Leffler’s research groups at the department of medical
biochemistry and biophysics, in particular by Amit Zeisel and Ana Muños
Manchado. It also involved researchers from Karolinska Institutet’s
Department of Oncology-Pathology, and Uppsala University.
The study was financed with grants from several bodies, including
the European Research Council, the Swedish Research Council, the Swedish
Cancer Society, the EU’s Seventh Framework Programme, the Swedish
Society of Medicine, the Swedish Brain Fund, Karolinska Institutet’s
strategic programme for neuroscience (StratNeuro), the Human Frontier
Science Program, the Åke Wiberg Foundation and the Clas Groschinsky
Memorial Fund.
Karolinska Institutet - a medical university: ki.se/english
http://ki.se/pressroom
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