L1.1.3.2.2: Myelin Sheaths

• MYELIN SHEATHS

  ● “Gift wrap”

  ● White, fatty material covering axons (waxy appearance)

  ● Protects and insulates fibers

  ● Speeds nerve impulse transmission
• MYELIN SHEATHS

  ● Speeds nerve impulse transmission

  ○ SCHWANN CELLS

  ○ OLIGODENDROCYTES
• ○ SCHWANN CELLS — wrap axons in jelly roll-like fashion (PNS) to form myelin sheath

  ■ Neurilemma — part of the schwann cell external to the myelin sheath

  ■ Nodes of Ranvier — gaps in myelin sheath along the axon
• ○ OLIGODENDROCYTES — produce myelin sheaths around axons of the CNS; lacks neurilemma (plays a role in fiber regeneration)
• Multiple Sclerosis (MS)

  - An autoimmune disease that destroys the myelin sheaths around CNS fibers by converting them to hardened sheaths called scleroses

  - When this happens, nerve signals do not always reach the intended target

  - EFFECTS: visual and speech disturbances, losing the ability to control one’s own muscles, and become increasingly disabled

  - Basically, the person’s own system attacks a protein component of the sheath