Glial Myelination Flashcards
Define Glial cells
make up supporting structures of CNS and PNS
Glial cells out# neurons:
3:1 up to 10:1
Do glial cells have
synapses
processes
AP
No synpase
have processes
No AP
What is special about glial cells
retain mitotic ability into adult life
What is the major source of CNS cancers?
Gliosis–forming of glial scars: d/t maintained mitotic ability
What is largest and most numerous of all glia?
astrocytes
What are teh 2 major types of Astrocytes
Fibrous and Protoplasmic
Where are Fibrous astrocytes located?
What kind of processes do they have?
White matter
Long and thin
Where are Protoplasmic astrocytes located?
What kind of processes do they have?
Gray matter
short, thicker processes
What are GFAPs?
connective tissue of CNS
Funtions of astrocytes?
Structure support and repair K+ buffering NT and metabolite removal Have certain NT for specificity Provide glial guides for neuronal migration during devo In brain can serve as stem cells
How do Astrocyte provide support and repair of CNS?
GFAP act as CT of CNS
fill space and surround synapses
Engulf and degrade neuronal debris
How is K+ spatial buffering maintained in astrocytes?
while astrocyte itself is not electrically excitable, it maintins K+ gradient bc we dont’ want excessive K+… thus helps maintain membrane potential
How do astrocytes remove NT’s and metabolites?
via GLAST cycle to rapidly terminate signal. uptakes other NT’s as well
What is GLAST
glutamine-glutamate cycle
asrocytes take up excess glutamate and release it back into cell space as glutamine where it is taken up and re-synthesized into glutamate
What is the fnx of NT receptors on astrocytes?
can trigger Ca++ waves in astrocytes
These guys contribute to but aren’t the basis for BBB
astrocytes
How do astrocytes communicate?
gap junctions for glial signaling
What provides glial guides for neruonal migration during devo?
astrocytes
Which subset of glial cells can serve as stem cells for regeneration in the adult brain
astrocytes
Oligodendrocytes are
larger/smaller/same size as astrocytes
have fewer/more/same amt of processes
have flat/round/cuboidal nuclei
SMALLER
FEWER process
ROUND nuclie
Three types of oligos?
perineural
interfascicular
oligos in white matter
Where do oligodentrocytes myelinate?
CNS
How many axons can 1 oligo myelinate?
MANY axons
What is a potent inhibitor of axon outgrowth and regeneration?
Central myelin
What are 3 types of inhibitors of CNS axonal elongation?
- Myelin-associated glycoprotein (MAG)
- Neurite Inhibitor of 35-dKA (NI-35)
- Nogo gene and proteins
Where are MAG’s expressed
by Oligodendrocytes in periaxonal oligodendorglial membrane
What is the significance of MAG
maintains axon-myelin complexes: axon-glial signaling
Levels of MAG are high in ______ and _______
developing PNS and CNS
Level of MAG fall in ________ but not in _________
mature PNS
not in mature CNS
What is the Chondroitin sulfate proteoglycan expressed by?
Neurite inhibitor of 35 kDA (NI-35)
What is the function of Nogo gene and proteins?
inhibit regeneration of CNS axons
expressed by Oligos
NOT expressed by Schwann cells
Where do Schwann cells myelinate?
PNS
How many axons do Schwann cells myelinate?
1 schwann only myelinates 1 segment of 1 axon
1 PNS axon is myelinated by how many Schwann cells?
50-500 cells
Schwann cell basal lamina: laminin is what?
Schwann cell growth promoting factors
Peripheral nerve regeneration requires?
laminin
Schwann cells surround
myelinated/unmyeliated/both axons
BOTH
Cell adhesion molecules such as NgCAM are what to Schwann cells
growth-promoting factor
What is the smallest glial cell?
Microglia
Microglia have long/short processes
short
When do microglia increase in # and size
when neurons degererate
When are microglia recruited?
during injury, infection and seizure
What disease states activate microglia?
MS, Parkinsons, Alzheimers, AIDS related dementia
Function of migroglia?
phagocytose debris in CNS
Function of Ependymal cell?
Provide some barrier btwn brain and CSF
Ciliary motion helps with CSF circulation
produces CSF in choroid plexus
Where are ependymal cells located?
line vertebral ventricles and central canal
Type and fnx of junctions in ependymal cells
desmosomal jnxs so some substances in CSF can penetrate the brain
What forms choroid plexus?
modified ependymal cells + associated caps
Do ependymal cells have tight junx?
YES this is the basis for BBB
What has myelin in both inner and outter mesaxons?
myelination in PNS: schwann cells
PNS/CNS has NO outer mesaxon?
CNS
Apposed cytoplasmic faces make up:
major dense lines
Apposed EXTRACELLULAR faces of myelin make up:
Minor Dense Lines
Diameter range cutoff for myelinated axons
less then 1 micrometer
Myelin has high/low lipid content
and increase/decreases or stays same with axon diameter
Increases
MBP is present where?
Structual protein of CNS myelin
small amount in PNS myelin
This guys is on the cytoplasmic face of the myelin membrane and corresponds to the major dense line
MBP
MBP role in autoimmune disease
basis for CNS autoimmune disease: experimental allergic encephalomyelitis
MAG stands for
myelin associated glycoprotein
MAG is present:
CNS/PNS or both
both
When and where does MAG decrease
in Adult in the PNS
MOG stands for
Myelin oligodendricyte glycoprotein
Where is MOG present
ONly in CNS
Located on surface of oligos and implicated as a target antiG in autoimmune aspect of CNS demyleinateing disease
MOGs
What part of Node of Ran is exposed to extracellular surface
axolemma
NOR has high conc of what type of voltage gated channels?
Na+
Internodes are usually about:
1-2 mm (larger axons = larger internodes)
Where does axon branching of myelinated axons occur
always at nodes
PNS nodes are covered by what?
Schwann cell cytoplasm
CNS nodes:
are bare
Location of Schmidt Lanterman Clefts
PNS
These guys are the “split” in major dense lines filled with Schwann cell cytoplasm
Schmidt Lanterman Clefts in PNS
Function of Schmidt Lanterman Clefts
cytoplasmic nutrients to inner clefts
Longitudinal incisures are located in CNS or PNS
CNS
Schmidt-Lanterman incisures are located in CNS or PNS
PNS
What are unmyelinated axons in PNS surrounded by?
Schwann cell cytoplasm and basal lamina
Chrnoic demyelinating disease of CNS
MS
Cause of MS
autoimmunde with genetic and environmetal risk factors
in MS what results in CNS due to demyelination
Gliosis
Symptoms of MS
abnormal or slowed conduction of AP
disruption to BBB and acute inflammation
periods of remission and relapse
Does MS affect sensory or motor axons?
Both— can lead to paralysis
Acute inflammatory disease of PNS
Guillian Barre
What does GB attack?
myelin of PNS nerves for skin and muscle
GB is autoimmune against:
myelin proteins PO and PMP
What difficulties do you have with GB?
sensory perception and motor coordination
