Ion Channel Proteins
Visual Cortex Areas
- When light waves strike the retina, photoreceptor cells generate electrochemical signals, which are relayed to the cerebral cortex for processing.
- Visual image processing begins in the primary visual cortex (V1), which is primarily located along the superior and inferior sides of the calcarine fissure on the medial side of the occipital lobe (Broadmann area 17).
- A small segment is also present on the lateral side of the cortex. V1 is also called the striate cortex due to its striped microscopic appearance.
- The visual pathway from the eyes to the primary visual cortex passes through the center of the brain.
- Ganglion cell neurons carry the visual signals generated by the retina to the optic nerves in the back of the eyes.
- After exiting eyes, the ganglion cell axons from the medial halves of each eye cross over at the optic chiasm.
- They then proceed to the lateral geniculate nuclei in the right and left thalami. A second set of neurons carries the visual signals to the primary visual cortex from the thalami.
- In the primary visual cortex, six layers of cells extract basic information about the edges, depth, orientation, motion, and color of objects in the visual field.
- The primary visual cortex is retino-topically organized, so each part the visual field is processed by a specific part of the cortex.
- From the primary visual cortex, two pathways transfer information forward to visual association areas, where visual signals are further interpretated and given additional meaning.
- A ventral stream passes through the secondary visual cortex (extrastriate cortex; Broadmann areas 18 and 19) and extends downward into the inferior temporal gyrus.
- The processing done by neurons in this pathway allows us to recognize faces and objects based on their size, shape, and color (what objects are?).
- A dorsal stream passes through the secondary visual cortex and extends upward to the posterior parietal cortex.
- Neurons in this pathway provide information about the motion of objects (where object are?).
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