Myelin Sheath Formation by Schwann Cells

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17 Terms

1
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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

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What is the role of cholesterol in myelin sheath formation?

Essential for assembling the myelin sheath

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What determines Schwann cell survival, maturation and myelination?

The expression of Neuregulin-type III on the axonal surface

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Which axons do Schwann cells myelinate?

Axons with large diameter that transmit electrical signals at highest speed

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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

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Where are Schwann cells located

In the PNS where they envelope axons

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What are myelinated nerves?

Axons that have myelin wrapped around them

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What is the structure of myelin as seen under an electron microscope?

Appears as alternating wide, dense lines and narrower less dense lines #00b6ee

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What is the major dense line in myelin? #04e5aa

Represents the fused cytoplasmic surfaces of the Schwann cell plasma membrane

<p>Represents the <span style="color: blue"><strong>fused cytoplasmic surfaces</strong></span><strong> </strong>of the <span style="color: blue"><strong>Schwann cell plasma membrane</strong></span></p>
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<p>What is the<span style="color: green"> <strong>intraperiod line</strong></span><strong> </strong>in <span style="color: #04e5aa"><strong>myelin</strong></span></p>

What is the intraperiod line in myelin

Represents the apposing outer leaflets of the Schwann cell plasma membrane

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What are intraperoid gaps?

Small gaps within the intraperiod line between spiraled layers of myelin sheath

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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

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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

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How many axons can a Schwann cell myelinate?

Only one internode of a single axon

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How does myelination differ between the CNS and PNS

CNS: Oligodendrocytes myelinate multiple axons

PNS: Schwann cells myelinate only 1 axon

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When are motor nerves and sensory roots fully myelinated?

Motor nerves: Nearly fully myelinated at birth

Sensory roots: Myelinated several months later

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When can Schwann cells can envelop multiple axons?

When enveloping unmyelinated axons