White matter

White matter is central nervous system tissue composed mainly of myelinated axons that connect neural regions. Its myelin-rich bundles support communication between parts of the brain and spinal cord.

Myelin: Myelin is a lipid-rich insulating sheath around many axons that increases the speed and efficiency of neural signaling. Myelin surrounds many white-matter axons and gives the tissue much of its pale appearance.
Gray matter: Gray matter is central nervous system tissue rich in neuronal cell bodies, dendrites, synapses, and unmyelinated fibers. Its cell-body-rich organization contrasts with the myelinated axon bundles dominant in white matter.
Diffusion MRI: Diffusion MRI is a magnetic resonance imaging method that measures the directional movement of water in tissue. Water diffusion patterns help estimate the orientation of white-matter fibers.
Corpus callosum: The corpus callosum is the largest bundle of commissural fibers connecting the cerebral hemispheres. It is a prominent white-matter structure carrying signals between the two hemispheres.
Axon: An axon is a neuron’s elongated projection that conducts electrical signals away from its cell body. Axons form the long-distance fibers bundled within white matter.
Neuroglia: Neuroglia are non-neuronal cells in nervous tissue that support, protect, and regulate neurons. Glial cells maintain white matter and produce or support its myelin.
Diffusion tensor imaging: Diffusion tensor imaging is an MRI technique that models directional water diffusion with tensors to study tissue structure. It maps white-matter organization by estimating the dominant direction of diffusion.
Internal capsule: The internal capsule is a compact white-matter pathway carrying fibers between the cerebral cortex and brainstem or spinal cord. Its tightly packed fibers make it a major route through cerebral white matter.
Saltatory conduction: Saltatory conduction is the rapid propagation of action potentials between gaps in a myelin sheath. Myelinated white-matter axons use this mode of signaling to transmit impulses quickly.
Node of Ranvier: A node of Ranvier is a gap between adjacent myelin segments along an axon. These gaps enable saltatory conduction along myelinated white-matter fibers.

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