兰氏结（英语：Nodes of Ranvier）又名郎氏结，是神经元的一部分，以首位描述该结构的法国科学家兰维尔（Louis-Antoine Ranvier）为名。

神经元的轴突包覆着髓鞘，兰氏结是神经元上每隔数毫米就会出现的没有髓鞘的部分。

跳跃传导学说认为，因为在兰氏结之间的结间区的电阻极高，而在结区的电阻极低，并且轴突膜仅在结区可接触细胞外液，所以，局部电流必须在兰氏结处穿出膜在髓鞘处形成回路，进行跳跃式传导。

虾的内侧大纤维则没有兰氏结。

Nodes of Ranvier, also known as myelin sheath gaps, are periodic gaps in the insulating myelin sheaths of myelinated axons where the axonal membrane is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, allowing them to participate in the exchange of ions required to regenerate the action potential. Nerve conduction in myelinated axons is referred to as saltatory conduction (from the Latin saltare, to hop or leap) because of the manner in which the action potential seems to "jump" from one node to the next along the length of the axon.