Myelin sheath
Stratum myelini
NervousNervesWhole body
- What it is
- Segments of fatty insulation wrapped around the axon in dozens of tight spiral layers - made by Schwann cells in peripheral nerves and by oligodendrocytes in the brain and spinal cord.
- Function
- Insulates the axon so the impulse jumps from gap to gap (saltatory conduction), raising conduction speed from about 1 m/s to as much as 120 m/s.
- Size
- Each internode 0.2-2 mm long; sheath up to ~2 micrometres thick
- Clinical note
- Multiple sclerosis strips myelin in the brain and cord; Guillain-Barre syndrome attacks peripheral myelin, causing rapidly ascending weakness.