求翻译：神经冲动只能由传入神经元向传出神经元的方向进行当神经冲动在中枢部分传布时，不能逆传。这种单向传布的特征由中枢内突触传递的特性决定。因此，在反射弧中兴奋只能从脊髓背根传入，由腹根传出，而不能相反，即背根是感觉性的，腹根是运动性的，这个规律叫做贝尔-马让迪定律。是什么意思？

Nerve impulses only from afferent neurons to the direction of the efferent neurons, nerve impulses in the central part of the spread, not retrograde. This one-way spread characteristics determined by the characteristics of synaptic transmission in the central. Therefore, excited only in the reflex a

Only by nerve impulses from the nerves to the neurons in the opposite direction when nerve impulses in the central part is transmitted, not the reverse. This one-way spread by the characteristics of the central characteristics of the pass. Therefore, the excitement can only be reflected in an arc fr

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