QUESTION: Myelin sheath is produced by
ANS: The myelin sheath is primarily produced by two types of glial cells in the nervous system:
- Oligodendrocytes in the central nervous system (CNS)
- Schwann cells in the peripheral nervous system (PNS)
Oligodendrocytes (CNS):
- Oligodendrocytes are responsible for producing and maintaining the myelin sheath in the central nervous system.
- Each oligodendrocyte can extend multiple processes, and each process can myelinate multiple nearby axons.
- Oligodendrocytes wrap their processes around the axons, forming compact layers of myelin that insulate and protect the axons.
Schwann Cells (PNS):
- Schwann cells are responsible for the production of the myelin sheath in the peripheral nervous system.
- Each Schwann cell myelinates a single segment of an axon.
- The Schwann cell wraps itself around the axon multiple times, creating layers of myelin and leaving small gaps called the nodes of Ranvier between adjacent Schwann cells.
- This arrangement allows for saltatory conduction, where the action potential “jumps” from one node of Ranvier to the next, increasing the speed of signal transmission.
| Aspect | Central nervous system | Peripheral nervous system |
| Cell Type | · Oligodendrocytes | · Schwann cells |
| Location | · Found within the CNS | · Found within the PNS |
| Myelination | · One oligodendrocyte myelinates multiple axons | · One Schwann cell myelinates a single axon |
| Myelin Segment | · Internode | · Internode |
| Speed of Conduction | · Slower conduction speed due to longer internodal distances | · Faster conduction speed due to shorter internodal distances |
| Nodes of Ranvier | · Multiple myelinated axons share Nodes of Ranvier | · Each myelinated axon has its own Nodes of Ranvier |
| Regeneration Potential | · Limited regeneration potential due to inhibitory factors | · Higher regeneration potential due to Schwann cells’ ability to guide axonal regrowth |
| Disease Implications | · Multiple sclerosis,
· Leukodystrophies |
· Peripheral neuropathy
· Guillain-Barré syndrome · Charcot-Marie-Tooth disease |