Anatomy of the Human Visual Pathway
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| Year of publication | 2017 |
| Type | Chapter of a book |
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| Description | Vision is the primary sense in humans. There are approximately one million axons in the optic nerve, constituting almost 40% of the total number of axons in all cranial nerves. The primary sensors for sight are the 130 million rods and seven million cones found in the retina. With the release of glutamate, they transform electromagnetic waves of light with a wavelength between 400 and 700 nm to graded changes of the membrane potential. The signal from photoreceptors continues to the bipolar cells and then to the retinal ganglion cells. Their axons pass through the optic nerve, the optic chiasm, form the optic tract, and reach the lateral geniculate body of the thalamus. The axons coming from the nasal hemiretina are crossed in the optic chiasm, while axons from the temporal hemiretina stay uncrossed. Neurons of the lateral geniculate body send their axons to the optic radiation and terminate in the primary visual cortex - the striate area in the ipsilateral occipital lobe where the first analysis of visual information is performed. Further processing takes place in extrastriate visual areas in the occipital, parietal, and tem- poral lobes. The visual pathway shows a precise retinotopical organiza- tion at all levels that gives the anatomical background for symptoms when some part of optic pathway is damaged. |