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What forms the myelin sheath in schwann cells? #04e5aa
The plasma membrane of Schwann cells that contains high amounts of lipids and cholesterol
What is the role of cholesterol in myelin sheath formation?
Essential for assembling the myelin sheath
What determines Schwann cell survival, maturation and myelination?
The expression of Neuregulin-type III on the axonal surface
Which axons do Schwann cells myelinate?
Axons with large diameter that transmit electrical signals at highest speed
What do Schwann cells do with slow conducting axons?
Slow conducting axons are arranged in bundle-like structure and is engulfed by non-myelinating Schwann cells
Where are Schwann cells located
In the PNS where they envelope axons
What are myelinated nerves?
Axons that have myelin wrapped around them
What is the structure of myelin as seen under an electron microscope?
Appears as alternating wide, dense lines and narrower less dense lines #00b6ee
What is the major dense line in myelin? #04e5aa
Represents the fused cytoplasmic surfaces of the Schwann cell plasma membrane
What is the intraperiod line in myelin
Represents the apposing outer leaflets of the Schwann cell plasma membrane
What are intraperoid gaps?
Small gaps within the intraperiod line between spiraled layers of myelin sheath
Define internal meaxon and external mesaxon
Internal mesaxon: The intraperiod line in contact with axon
External mesaxon: The intraperiod line in contact with the Schwann cell body
How does the myelination process occur?
A Schwann cell wraps its plasma membrane around an axon which squeezing the cytoplasm back into its body forming the myelin sheath
How many axons can a Schwann cell myelinate?
Only one internode of a single axon
How does myelination differ between the CNS and PNS
CNS: Oligodendrocytes myelinate multiple axons
PNS: Schwann cells myelinate only 1 axon
When are motor nerves and sensory roots fully myelinated?
Motor nerves: Nearly fully myelinated at birth
Sensory roots: Myelinated several months later
When can Schwann cells can envelop multiple axons?
When enveloping unmyelinated axons