Here we report that mice with PN specific TLR4 deletion (TLR4PKO mice) exhibited motor impairments consistent with cerebellar ataxia, reduced PN dendritic arborization and spine density, fewer parallel fiber (PF) – PN and climbing fiber (CF) – PN synapses, reduced BK channel expression, and impaired BK-mediated after-hyperpolarization, collectively leading to abnormal PN firing. Here, KCNMA1 is linked to aceruloplasminemia.