White matter

<p>White matter refers to areas of the <a href="/facts/Central_nervous_system/k8I6To97">central nervous system</a> that are mainly made up of <a href="/facts/Myelin/DKgJB8s8">myelinated</a> <a href="/facts/Axon/5DCd4wLo">axons</a>, also called <a href="/facts/Nerve_tract/GtK41Ck4">tracts</a>. Long thought to be passive tissue, white matter affects <a href="/facts/Learning/lehEKRjC">learning</a> and brain functions, modulating the distribution of <a href="/facts/Action_potential/Sz8yCRqx">action potentials</a>, acting as a <a href="/facts/Relay/NQcb9usW">relay</a> and coordinating communication between different brain regions.
</p><p>White matter is named for its relatively light appearance resulting from the <a href="/facts/Lipid/TdQR87HX">lipid</a> content of <a href="/facts/Myelin/DKgJB8s8">myelin</a>. Its white color in prepared specimens is due to its usual preservation in <a href="/facts/Formaldehyde/Ck8RLfqk">formaldehyde</a>. It appears pinkish-white to the naked eye otherwise, because myelin is composed largely of lipid tissue veined with <a href="/facts/Capillaries/4BIzKJAe">capillaries</a>. 
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White matter open-in-new

White matter