A myriad of small concentrated nerve cell accumulations (nuclei) interspersed among the nerve fibre masses that penetrate the bridge (pons) from the midbrain (mesencephalon).
The pons nuclei receive signals from the cerebral cortex, especially much from the forehead (frontal) and parietal lobes of one hemisphere and transmit them across the midline (tractus ponto-cerebellaris) and through the middle cerebellar arm to the opposite side of the cerebellar hemisphere.
Most pathway systems that run through the bridge emit lateral branches of the pons nuclei, including the tractus cortico-nuclearis, tractus cortico-spinalis and tractus reticulo-spinalis.