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•  The myelination of nerve fibres allows for saltatory conduction

In certain neurons, the axon may be covered by a fatty white substance called myelin which functions as an insulating layer

  • Myelin is a mixture of protein and phospholipids that is produced by glial cells (Schwann cells in PNS; oligodendrocytes in CNS)

The main purpose of the myelin sheath is to increase the speed of electrical transmissions via saltatory conduction

  • Along unmyelinated neurons, action potentials propagate sequentially along the axon in a continuous wave of depolarisation
  • In myelinated neurons, the action potentials ‘hop' between the gaps in the myelin sheath called the nodes of Ranvier
  • This results in an increase in the speed of electrical conduction by a factor of up to 100-fold

Impulse Propagation Along a Myelinated Neuron

myelin sheath


Not all neurons within the nervous system are insulated with a myelin sheath

  • The advantage of myelination is that it improves the speed of electrical transmission via saltatory conduction
  • The disadvantage of myelination is that it takes up significant space within an enclosed environment

Regions of the nervous system composed of myelinated axon tracts appear as white matter, all other areas appear as grey matter

  • Grey matter consists of neuronal cell bodies and dendrites, as well as support cells (glial cells) and synapses 

Transmission Speeds in Unmyelinated and Myelinated Neurons