Diameter affects.......

-Diameter and myelination affect passive properties and therefore conduction velocity (CV). Increasing the diameter increases CV, 

Increasing Myelination......

-Myelination greatly decreases cm and therefore increases conduction velocity

-- Myelination also increases rm  and effective spread of local circuit

  currents (reduced leakage) 

Ephaptic transmission 

Ephaptic transmission is electrical cross-talk between axons. It occurs when extracellular portions of local circuit currents of nearby axons excite demyelinated axons that are no longer insulated from the currents.

 common demyelinating neuropathies of the CNS and PNS

Multiple sclerosis (CNS) and Guillain Barré syndrome (PNS)

Some defects of myelination are genetic

Charcot-Marie-tooth disease is common inherited peripheral neuropathy affecting 1:2,500

- Type 1b: point mutations in peripheral myelin protein (P0) gene

- Type 1a (autosomal dominant):  over-expression of peripheral

   myelin protein (PMP22) due to gene duplication

-  X-linked: defect in gap junction protein of myelin lamellae 

   (connexin32)

Symptoms

-  Greatly decreased conduction velocity

-  Cyclical demyelination/myelination

-  Impaired gait, deformed contracted foot (pes cavus) are long-

  term hallmarks of chronic disease

Other myelin diseases

-   Some diseases of CNS myelin ("leukodystrophies") are also   genetic

Comparison of chemical and electrical synapses

  coupled cells, through channels formed by connexin proteins

  (unlike at chemical synapses)

  -Fast, but complex integration cannot

     occur

   of positive and negative, fast and

   slow signals