08_Glial Cells_Q and A_Jonathan Flashcards
Glial cells in the CNS represent a heterogeneous population of cells with a diverse and largely unknown set of functions. These are the most numerous cells of the CNS, and it has been estimated that they encompass 90% of cells in the human CNS (perhaps even greater percent in other species and probably slightly less in rodents – 65%).
Glial cells in the CNS represent a heterogeneous population of cells with a diverse and largely unknown set of functions. These are the most numerous cells of the CNS, and it has been estimated that they encompass 90% of cells in the human CNS (perhaps even greater percent in other species and probably slightly less in rodents – 65%).
Glia are classically broken down into two categories:
macroglia and microglia.
Where are Macroglia derived?
• from the neuroectoderm.
What are the macroglia?
• oligodendrocytes o perineuronal o intrafascicular • astrocytes o fibrous o protoplasmic • ependymal cells • choroid plexus • radial glia
Where are microglia derived from?
• mesoderm
What are microglia?
• monocyte/macrophage
What are Oligodendrocytes?
axonal ensheathing cells primarily found in the white matter
What are Perineuronal oligodendrocytes?
found close to neurons in the gray matter and probably don’t myelinate, share some ultrastuctural features with other oligos; controversial and some feel they may be a completely new type of cell.
What are Interfascicular oligodendrocytes?
myelinate axons to enhance electrical conduction.
What are Fibrous astrocytes?
primarily in WM, long fibrillar processes that envelope Nodes of Ranvier.
What are Protoplasmic astrocytes?
primarily in GM, sheet-like processes that surround synapses.
What are Ependymal cells?
– specialized glial cells with cilia that form a tight columnar type alignment along ventricular and central canal linings. Choroid plexus, also specialized glial cells produce CSF, while the ependymal cells help circulate the CSF.
What are Radial glia?
– specialized glia that act as “active” scaffolding in the developing CNS.
What are Microglia?
- are very different types of cells that are specialized monocyte/macrophage type cells derived from the mesoderm.
- migrate into CNS from bone marrow stem cells.
- They are believed to assist in the extensive remodeling of the fetal CNS by phagocytizing cells that die normally by apoptotic cell death.
What do microglia look like post natally?
- In post natal life they are small, dense, elongated nuclei without identifiable cytoplasm.
- Special stains to reveal their cytoplasm show it to be arranged as thin branches radiating from the nuclear zone.
- Microglia establish individual, non-overlapping territories.
What percent of the nervous system is microglia?
o They comprise about 8-10 percent of all CNS cells.
What do microglia do after development?
- Not well understood
- They may lie fairly quiescent in surveillance for some brain insult when they then become activated take on important neuroimmunologic phagoctyic functions.
- These cells will be discussed in greater detail in neuropathology next year.
What are Schwann cells and where are they derived?
- from neural crest and are the glial cells of the peripheral nervous system.
- They carry out similar functions to astrocytes, oligodendrocytes, and microglia in the peripheral nervous system.
- They ensheathe motor and sensory axons to improve conduction velocities.
What is the function of Schwann cells in the neuromuscular junction?
• They are also important components of the synapse at the NMJ and have the capacity to ingest tissue debris and promote regeneration after injury.
Where do glial cells develop?
• Glial cells develop after the neurons within the subventricular zone (SVZ).
What are the first two cell types in the SVZ to develop?
• radial glia and neurons.
Explain glial cell development?
- During early brain development a dense collection of progenitor cells accumulate in the (SVZ).
- Two cell types are among the first to mature and leave this area: the radial glia and neurons.
- The radial glia have long processes that span the length of the developing cortex from pia to ventricle.
- It’s along these processes that the migrating young neurons move to populate the cortical plate.
- Once most of the neurons have left the SVZ the remaining progenitor cells within this germinal matrix then develop into protoplasmic astrocytes or oligodendrocytes.
How do astrocytes (and other glia?) migrate into the developing brain? Are the migrating cells preformed cell lines or pleuripotent?
- Recent data suggests that the astrocytes migrate up the radial glia similar to the neurons.
- Additional studies also suggest that some the migrating cells are pluripotent meaning that they can develop into neurons or astrocytes.
During what month in development are neurons born?
Astrocytes?
Oligodendrocytes?
- neurons are born in the second month
- astrocytes in the third month
- oligodendrocytes in the fourth and fifth months.
