Systems Biology
The total area you can see is called the visual field, which is divided into a left and right half. Light from these halves maps onto the opposite sides of each retina. Axons and retinal ganglion cells exit the eye at the optic nerve to transmit information about the visual field to the brain. Temporal retina fibers stay on the same side of the brain as the eye they originated from, while nasal retina fibers cross to the opposite side at the optic chiasm. This places all fibers from the right visual field together on the left side of the brain and vice versa.
Each optic tract synapses in the same-side lateral geniculate nucleus (LGN) of the thalamus. Optic radiations then transport visual information from each LGN to the primary visual cortex for final processing, before that information gets shared out to the rest of the brain. There are two main overarching visual pathways: the parvo pathway, which recognizes color and form and functions best on stationary objects, and the magno pathway, which recognizes information about the movement of objects. Through parallel processing, both pathways are active simultaneously, and the primary visual cortex interprets them together as a single image.
Lesson Outline
<ul> <li>Division of visual field <ul> <li>Left half & right half</li> <li>Light lands on the opposite of the retina (left on right side, right on left side) due to light bending through cornea and lens</li> </ul> </li> <li>Photoreceptors and retinal ganglion cells <ul> <li>Transformation of light to chemical signals, then to electrical impulses</li> <li>Signal exits the eyes via the optic nerves</li> </ul> </li> <li>Temporal and nasal retina fibers <ul> <li>Nasal retina fibers cross over at optic chiasm (temporal stay on the same side they started on)</li> <li>Crossover allows left-field signal from both eyes to be processed on the right side of the brain, and right-field signal on the left side</li> </ul> </li> <li>Optic tracts and the lateral geniculate nucleus (LGN) <ul> <li>Integration of visual information with input from other brain areas</li> <li>Location of LGN in the thalamus</li> </ul> </li> <li>Primary visual cortex <ul> <li>Location at the back of the occipital lobe</li> <li>Optic radiations as the final axon pathways</li> </ul> </li> <li>Parvocellular (P) and magnocellular (M) pathways <ul> <li>P pathway: color, form, and detail - associated with stationary objects</li> <li>M pathway: motion - faster response but less detail</li> </ul> </li> </ul>
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FAQs
The visual field refers to the entire area that can be seen when the eyes are focused on a central point. It includes central and peripheral vision. Visual field information is processed in the primary visual cortex (V1), which is located in the occipital lobe of the brain. V1 receives and processes input from the retina, via the optic nerve, lateral geniculate nucleus, optic chiasm, optic tract, and optic radiations, before sending the processed information to higher visual areas.
The retina is a thin layer of neural tissue lining the back of the eye. It contains photoreceptor cells, called rods and cones, that detect light and generate electrical impulses. These impulses are relayed to bipolar and ganglion cells within the retina, which process the signals further and send them through the optic nerve to the lateral geniculate nucleus (LGN) in the thalamus. The retina is essential for converting light into neural signals and plays a crucial role in early stages of visual processing.
The optic chiasm is a structure where the optic nerves from each eye meet and partially cross. At this point, the fibers carrying information from the nasal (inner) half of each retina cross to the opposite side of the brain, while those from the temporal (outer) half remain on the same side. This results in the formation of the optic tract, which carries information from each visual field (right and left) to the respective contralateral hemisphere. This arrangement ensures that information from both eyes, representing both the left and right visual fields, is integrated and processed in the brain.
The parvocellular and magnocellular pathways are two parallel visual processing pathways that originate in the retina and extend to the lateral geniculate nucleus. The parvocellular pathway consists of P-cells, which are primarily involved in processing high spatial resolution, fine detail, and color information. In contrast, the magnocellular pathway consists of M-cells, which process motion, depth, and low spatial resolution information. These two pathways help to process distinct aspects of visual information and enable the brain to build a coherent and detailed understanding of the visual environment.
The optic radiations, also known as geniculocalcarine tracts or visual radiations, are nerve pathways that connect the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex in the occipital lobe. They carry processed visual information from the LGN to the primary visual cortex, where further processing occurs. The optic radiations consist of axonal fibers running through different regions of the brain, depending on whether they are part of the parvocellular or magnocellular pathways. These fibers help transmit visual information efficiently and accurately from the thalamus to the cortex for higher-level processing.
