The magnocellular and parvocellular pathways (M and P pathways) are the major pathways of the visual system, with distinct histologic and physiologic properties.
Visual pathways transfer information through different neural pathways. The largest path (approximately 80% of the nerve fibers) is the parvocellular pathway that transfers all color information and high contrast black and white information. Its nerve fibers are thin and transfer information relatively slowly. The magnocellular pathway (10% of the fibres) transfers all motion related information and low contrast black and white information. Its fibers are thick and have high speed of information transfer.
The magnocellular pathway carries information from the large retinal ganglion cells to the large cells in the LGN (magno=large in Latin) and from there to the primary visual cortex, V1 within the retinocalcarine pathway and over the SC to numerous subcortical functions and to the parietal visual functions. This magnocellular pathway carries all transient, motion related visual information and low contrast black-and-white information. Since the fibers are thick, the speed of transfer is high. The magnocellular pathway is more prominent in the tectal pathway than in the retinocalcarine pathway.
The parvocellular pathway from the small retinal ganglion cells carries all color information and is effective in carrying high contrast black-and-white information. The nerve fibers are thin and thus the speed of transfer is low. In the optic nerve 80% of the nerve fibres are parvocellular fibers and 10% of the fibres are magnocellular fibers.