Myelin Sheath Formation by Schwann Cells

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