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脑白质是由许多有髓鞘的轴突组成，白质和灰质共同组成中枢神经系统，白质是中枢神经系统内信息快速传递的基础。有髓神经通路主要是由少突胶质细胞、星形胶质细胞及少量的小胶质细胞和少突胶质前体细胞构成。大部分白质内的神经递质信号主要存在于神经细胞胞体外，这提示这些神经递质除了具有完成神经元与神经元之间信息传递的功能外，还有其他生理功能。白质中的神经递质信号种类很多，已经证实的有谷氨酸能、嘌呤能（ATP和腺苷）、GABA能、甘氨酸能、肾上腺素能、胆碱能、多巴胺能、血清素能等信号递质，通过与各种离子型或代谢型受体结合发挥作用。轴突和胶质细胞都可以释放神经递质，也可以表达相应的受体。白质内神经递质信号的生理功能还需进一步研究，但研究已经证实谷氨酸和ATP介导的信号可激活胶质细胞上的钙离子通道，并调节轴突的传导功能。某项研究显示，在动作电位传播的过程中，轴突释放神经递质并与胶质细胞上的受体结合，通过少突胶质细胞来调节星形胶质细胞的稳态和髓鞘形成。星形胶质细胞也释放神经递质，与轴突上的受体相结合，增强动作电位的传播，维持信号电位沿长的轴突传播。白质内神经递质种类的多样性，提示它们有多种功能，对信号的传递有重要作用。白质内的神经递质信号现象很有可能也存在于大脑皮质和灰质，在这些部位的神经递质对于大脑的高级认知功能有更重要的作用。“,”White matter (WM) tracts are bundles of myelinated axons that provide for rapid communication throughout the CNS and integration in grey matter (GM). The main cells in myelinated tracts are oligodendrocytes and astrocytes, with small populations of microglia and oligodendrocyte precursor cells. The prominence of neurotransmitter signaling in WM, which largely exclude neuronal cell bodies, indicates it must have physiological functions other than neuron-to-neuron communication. A surprising aspect is the diversity of neurotransmitter signaling in WM, with evidence for glutamatergic, purinergic (ATP and adenosine), GABAergic, glycinergic, adrenergic, cholinergic, dopaminergic and serotonergic signaling, acting via a wide range of ionotropic and metabotropic receptors. Both axons and glia are potential sources of neurotransmitters and may express the respective receptors. The physiological functions of neurotransmitter signaling in WM are subject to debate, but glutamate and ATP-mediated signaling have been shown to evoke Ca (2+) signals in glia and modulate axonal conduction. Experimental findings support a model of neurotransmitters being released from axons during action potential propagation acting on glial receptors to regulate the homeostatic functions of astrocytes and myelination by oligodendrocytes. Astrocytes also release neurotransmitters, which act on axonal receptors to strengthen action potential propagation, maintaining signaling along potentially long axon tracts. The co-existence of multiple neurotransmitters in WM tracts suggests they may have diverse functions that are important for information processing. Furthermore, the neurotransmitter signaling phenomena described in WM most likely apply to myelinated axons of the cerebral cortex and GM areas, where they are doubtless important for higher cognitive function.