Glossary
Myelination
What is myelination?
Myelination is the process of forming a myelin sheath around nerve fibers (axons), dramatically increasing the speed and efficiency of neural signal transmission. It is a key mechanism of brain development and learning.
A myelinated axon has a myelin sheath; to myelinate is to form that sheath around an axon.
How it works
Myelin is an insulating sheath around axons. Oligodendrocytes form it in the central nervous system, and Schwann cells form it in peripheral nerves. Myelin affects conduction speed and timing. Human myelination continues for decades and can be influenced by experience; it does not have one universal completion age.
The sheath forms in segments separated by small gaps called nodes of Ranvier. An action potential at one node produces local electrical current that spreads beneath the insulated segment and brings the next node to the point of generating another action potential. This sequence is saltatory conduction, often described as a signal “jumping” between nodes. The current still travels through the intervening axon; it does not skip space. Purves and colleagues explain this sequence.
Applied example
Compare how a signal propagates along an unmyelinated and a myelinated axon. In the unmyelinated axon, successive neighboring regions of membrane regenerate the action potential. In the myelinated axon, regeneration is concentrated at the nodes, with current spreading between them. This arrangement permits faster conduction without regenerating the impulse at every intervening membrane region. It does not imply a single speed multiplier for all nerves.
Researchers also compare white-matter measures before and after learning, but such a change still requires evidence about what changed in the tissue. Frequent use does not automatically mean more myelin.
Why it matters
Myelination contributes to neural communication and development. Development varies across pathways and people. An age cutoff is not a complete explanation of someone’s judgment or impulse control.
Evidence note: Fields (2008) describes prolonged development and research on activity-dependent myelination.