BSC 215 Lecture Notes - Lecture 25: Schwann Cell, Ependyma, Neurolemma
11 Jun 2018
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Neuroglia
Neuroglia (glia) are cells that support and protect neurons. The following four neuroglia
are found in the CNS:
• Astrocytes have numerous processes that give the cell a
star‐shaped appearance. Astrocytes maintain the ion
balance around neurons and control the exchange of
materials between blood vessels and neurons.
• Oligodendrocytes have fewer processes than astrocytes.
They wrap these cytoplasmic processes around neurons to
create an insulating barrier called a myelin sheath.
• Microglia are phagocytic macrophages that provide a
protective function by engulfing microorganisms and
cellular debris.
• Ependymal cells line the fluid‐filled cavities of the brain
and spinal cord. Many are ciliated.
Two kinds of neuroglia are found in PNS:
• Schwann cells (neurolemmocytes) wrap around axons to produce an
insulating myelin sheath. Schwann cells provide the same function in the PNS
as oligodendrocytes provide in the CNS.
• Satellite cells are located in ganglia, where they surround the cell bodies of
neurons.
Myelination
In the PNS, the myelin sheath is an insulation formed by Schwann cells around axons. Each
Schwann cell tightly wraps around the axon numerous times to form a multilayered insulation.
The last wrapping of the plasma membrane of the Schwann cell, the neurilemma, is loose and
contains the nucleus, cytoplasm, and organelles of the Schwann cell.
The myelin sheath consists of numerous Schwann cell wrappings along the
length of the axon. Spaces occur between adjacent Schwann cells, leaving
uninsulated areas, or neurofibral nodes (nodes of Ranvier), along the axons.
As an insulator, the Schwann cells interrupt the continuous conduction of a
nerve impulse along the axon. A signal is transmitted by local current in the
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Document Summary
Neuroglia (glia) are cells that support and protect neurons. The following four neuroglia are found in the cns: astrocytes have numerous processes that give the cell a star shaped appearance. Astrocytes maintain the ion balance around neurons and control the exchange of materials between blood vessels and neurons: oligodendrocytes have fewer processes than astrocytes. Two kinds of neuroglia are found in pns: schwann cells (neurolemmocytes) wrap around axons to produce an insulating myelin sheath. Schwann cells provide the same function in the pns as oligodendrocytes provide in the cns: satellite cells are located in ganglia, where they surround the cell bodies of neurons. In the pns, the myelin sheath is an insulation formed by schwann cells around axons. Schwann cell tightly wraps around the axon numerous times to form a multilayered insulation. The last wrapping of the plasma membrane of the schwann cell, the neurilemma, is loose and contains the nucleus, cytoplasm, and organelles of the schwann cell.
