The brain in of itself has no pain receptors.

大脑本身没有疼痛感受器。

And because your retinas don't have any pain receptors, your eyes have no way of warning you to stop.

而且因为你的视网膜没有痛觉感受器，你的眼睛无法警告你停下来。

In the case of migraines, the blood cells constrict, and then as the blood cells begin to relax, that physical relaxation stimulates the pain receptors and causes the pain.

在偏头痛的情况下，血细胞收缩，然后当血细胞开始放松时，这种物理放松刺激疼痛受体并导致疼痛。