A&P: Visual pathway

Optic chiasm

Flattened structure behind the optic nerve

Optic nerve

Optic chiasm

Hypothalamus

Pituitary gland

Prefixed optic chiasma

Lies more anteriorly over tuberculum sellae, pituitary tumor involves optic tract first.

Normal optic chiasma

Chiasm lies directly over sella

Expanding pituitary tumor involves chiasm first

Post fixed optic chiasm

Optic tracts

Cylindrical bundles of nerve fibres

Crosses nerve fibers

Nasal fibers of OD and OS

End at lamina 1,4, and 6 of LGN

Uncrossed nerve fibers

Temporal fibers of OD and OS

End at lamina 2,3, and 5 of LGN

Magnocellular layers

Layers 1 and 2 of LGN

Contains large cells

Carry signals for detection of movement and flicker

Parvocellular pathways

Layers 3-6 of LGN

Contains small cells

Accurate point spatial information for texture, shape, and fine depth vision

Koniocellular pathway

Function still not understood

Thought to be involved with color vision

Short-wavelength sensitive cone cells in retina

Optic radiations

Neurons of the LGB send their axons to the occipital corte

Baums loop

Made up of superior fibers of the retina (Process inferior visual field)

As they pass through parietal lobe, they form baums loop

Meyers loop

Made up of inferior fibers of the retina (Process superior visual field)

As they pass through the temporal lobe, they form meyers loop

Occipito temporal (Ventral) pathway

Begins at V1 of LGN (Foveal vision)
“What pathway”

Occipitoparietal (Dorsal) pathway

“Where” pathway

Movement, spatial awareness, locating objects