White matter is found in the deeper tissues of the brain (subcortical). It contains nerve fibers (axons), which are extensions of nerve cells (neurons). Many of these nerve fibers are surrounded by a type of sheath or covering called myelin. Myelin gives the white matter its color. It also protects the nerve fibers from injury. Also, it improves the speed and transmission of electrical nerve signals.
By comparison, gray matter is tissue found on the surface of the brain (cortical). It contains the cell bodies of neurons, which give gray matter its color.
Calabresi PA. Multiple sclerosis and demyelinating conditions of the central nervous system. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 411.
Haines DE, Mihailoff GA, Yezierski RP. The spinal cord. In: Haines DE, ed. Fundamental Neuroscience for Basic and Clinical Applications. 4th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 9.
Ransom BR, Goldberg MP, Arai K, Baltan S. White matter pathophysiology. In: Grotta JC, Albers GW, Broderick JP, et al, eds. Stroke: Pathophysiology, Diagnosis, and Management. 6th ed. Philadelphia, PA: Elsevier; 2016:chap 9.
Review Date 1/26/2017
Updated by: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.