Sjónrænna

Sjónrænna refers to the network of neurons involved in vision, spanning from the retina to higher visual centers in the brain. The term is used to describe the cells and connections that encode, relay, and interpret visual information for perception and behavior. Sjónrænna encompasses both early sensory neurons in the retina and the cortical neurons that process visual features such as edges, color, motion, and form.

In the retina, photoreceptors—rods and cones—transduce light into electrical signals. These signals propagate to bipolar cells and then to ganglion cells, whose axons form the optic nerve. Horizontal and amacrine cells provide lateral processing that shapes receptive fields and contrast sensitivity. The retina thus contains a layered network of sjónrænna that begin the encoding of visual scenes.

The optic nerves partly cross at the optic chiasm, so visual information from the left and right hemifields is routed to opposite sides of the brain. The signals continue through the optic tract to the lateral geniculate nucleus (LGN) of the thalamus, and from there via the optic radiations to the primary visual cortex (V1) in the occipital lobe. Retinotopic mapping is preserved, meaning neighboring retinal cells project to neighboring cortical areas.

Beyond V1, a hierarchy of extrastriate visual areas (V2, V3, V4, MT/V5, and others) progressively extracts complex features such as contour, color, depth, and motion. Visual information is processed through parallel pathways, including the magnocellular pathway (motion and luminance) and the parvocellular pathway (color and form), with further specialization in higher visual cortices.

Clinical relevance includes deficits from lesions along the visual pathway, such as scotomas or hemianopia, reflecting the organized flow of sjónrænna from the eye to perception.