GLIA!
WHAT ARE GLIA?
o Neuroglia = “nerve glue”
o the connective tissue of the nervous system,
consisting of several different types of cell
associated with neurons.
o Glia as cells: In the first decades of the
twentieth century, Pío del Río-Hortega was
able to specifically observe the fine
morphological intricacies of microglia. These
findings contradicted Cajal's views on cells
that he thought belonged to the same class as
oligodendroglia (the so called “third element”
of the nervous system), leading to a long-standing discussion. It was only in 1924 that Río-
Hortega's observations prevailed worldwide, thus recognizing microglia as a unique cell type.
For decades, microglia in normal, physiological conditions in the adult brain were considered
to be merely “resting,” and their contribution as “activated” cells to the neuroinflammatory
response in pathological conditions mostly detrimental. It was not until microglia were
imaged in real time in the intact brain using two-photon in vivo imaging that the extreme
motility of their fine processes was revealed. These findings led to a conceptual revolution in
the field: “resting” microglia are constantly surveying the brain parenchyma in normal
physiological conditions
CLASSIFICATION:
o NEURAL cells = neurones and glia
o Neuronal cells = neurones
o GLIA = Macroglia (larger) and Microglia (smaller)
o MACROGLIA:
-- Astrocytes
-- Radial glia (form the scaffold on which developing neurones migrate during nervous
system development. Change after development and can then take on different roles).
-- Oligodendroglia (myelinate CNS)
-- Schwann Cells (myelinate PNS)
These two myelinating glia insulate axons, and in an adult mammalian nervous system,
myelin is essential for the rate of transmission required.
OTHER GLIAL TYPES:
o Radial Glia - a transitory population of cells found during development. Act as a scaffolding
for neuronal development. Have long projections that extend from the inner to the outer
surface of the cortex. Neuronal progenitor cells migrate along them during development.
Can develop into other glial types or even neurones.
o Bergmann Glia, radial astrocytes of the cerebellum. Lie in the Purkinje cell layer and have
long projections that extend into the molecular layer. Each Bergmann glia ensheaths 2000-
6000 Purkinje cell synapses.
o Müller Glia, radial glia of the retina, with microglia like activity. Have projections that
contact every layer of the retina.
RADIAL GLIA:
, oEmbryonic scaffold throughout CNS
oGuides for radial migration of neurones
oProduce matrix and adhesion proteins
oOnce radial glia have performed their function of allowing neuronal migration, they
change into other glial types:
-- Adult radial glia persist in the cerebellum (Bergmann glia) and in the retina (Muller
cells)
OTHER GLIA:
o Ependymal cells:
-- Line the central canal and ventricles of the brain
-- Cuboidal cells but have no basement membrane
-- Have beating cilia when lining the ventricles
-- Specialised ependymal cells participate in the secretion of cerebral spinal fluid
(necessary for the movement of molecules around the brain)
o Glia express GFAP which can be labelled to identify the type of glial cell – different glia
express different types of GFAP
EMBRYONIC ORIGIN
o Different kinds of glia have distinct embryonic origins
o Neurones, Astrocytes and Oligodendrocytes from the neural tube
o Schwann Cells – from the Neural Crest
o Microglia – derived from macrophages (i.e. blood)
GLIOGENESIS
o Neuroepithelial stem cells can
differentiate to form neurones
or glial-restricted precursors,
which can then give rise to
different glial cell types
depending on the growth
factors they are exposed to.
o For instance, O2A progenitor
cells will go on to form
oligodendrocytes, or in culture
they can be forced to form type
2 astrocytes. No evidence that
type 2 astrocytes exist in the
brain (unlike type 1 astrocytes,
formed from astrocyte
precursor cells).
o No microglia
o No Schwann cells
WHAT ARE GLIA?
o Neuroglia = “nerve glue”
o the connective tissue of the nervous system,
consisting of several different types of cell
associated with neurons.
o Glia as cells: In the first decades of the
twentieth century, Pío del Río-Hortega was
able to specifically observe the fine
morphological intricacies of microglia. These
findings contradicted Cajal's views on cells
that he thought belonged to the same class as
oligodendroglia (the so called “third element”
of the nervous system), leading to a long-standing discussion. It was only in 1924 that Río-
Hortega's observations prevailed worldwide, thus recognizing microglia as a unique cell type.
For decades, microglia in normal, physiological conditions in the adult brain were considered
to be merely “resting,” and their contribution as “activated” cells to the neuroinflammatory
response in pathological conditions mostly detrimental. It was not until microglia were
imaged in real time in the intact brain using two-photon in vivo imaging that the extreme
motility of their fine processes was revealed. These findings led to a conceptual revolution in
the field: “resting” microglia are constantly surveying the brain parenchyma in normal
physiological conditions
CLASSIFICATION:
o NEURAL cells = neurones and glia
o Neuronal cells = neurones
o GLIA = Macroglia (larger) and Microglia (smaller)
o MACROGLIA:
-- Astrocytes
-- Radial glia (form the scaffold on which developing neurones migrate during nervous
system development. Change after development and can then take on different roles).
-- Oligodendroglia (myelinate CNS)
-- Schwann Cells (myelinate PNS)
These two myelinating glia insulate axons, and in an adult mammalian nervous system,
myelin is essential for the rate of transmission required.
OTHER GLIAL TYPES:
o Radial Glia - a transitory population of cells found during development. Act as a scaffolding
for neuronal development. Have long projections that extend from the inner to the outer
surface of the cortex. Neuronal progenitor cells migrate along them during development.
Can develop into other glial types or even neurones.
o Bergmann Glia, radial astrocytes of the cerebellum. Lie in the Purkinje cell layer and have
long projections that extend into the molecular layer. Each Bergmann glia ensheaths 2000-
6000 Purkinje cell synapses.
o Müller Glia, radial glia of the retina, with microglia like activity. Have projections that
contact every layer of the retina.
RADIAL GLIA:
, oEmbryonic scaffold throughout CNS
oGuides for radial migration of neurones
oProduce matrix and adhesion proteins
oOnce radial glia have performed their function of allowing neuronal migration, they
change into other glial types:
-- Adult radial glia persist in the cerebellum (Bergmann glia) and in the retina (Muller
cells)
OTHER GLIA:
o Ependymal cells:
-- Line the central canal and ventricles of the brain
-- Cuboidal cells but have no basement membrane
-- Have beating cilia when lining the ventricles
-- Specialised ependymal cells participate in the secretion of cerebral spinal fluid
(necessary for the movement of molecules around the brain)
o Glia express GFAP which can be labelled to identify the type of glial cell – different glia
express different types of GFAP
EMBRYONIC ORIGIN
o Different kinds of glia have distinct embryonic origins
o Neurones, Astrocytes and Oligodendrocytes from the neural tube
o Schwann Cells – from the Neural Crest
o Microglia – derived from macrophages (i.e. blood)
GLIOGENESIS
o Neuroepithelial stem cells can
differentiate to form neurones
or glial-restricted precursors,
which can then give rise to
different glial cell types
depending on the growth
factors they are exposed to.
o For instance, O2A progenitor
cells will go on to form
oligodendrocytes, or in culture
they can be forced to form type
2 astrocytes. No evidence that
type 2 astrocytes exist in the
brain (unlike type 1 astrocytes,
formed from astrocyte
precursor cells).
o No microglia
o No Schwann cells
