Visual Cortex
The Visual Pathway
1. Light must pass through the cornea, aqueous humor, lens and vitreous humor before reaching the retina. It must then pass through the inner layers of the retina to reach the photoreceptive layer of rods and cones.
2. When the photoreceptors are stimulated they transmit impulses to the bipolar cells that project to the ganglion cells of retina.
3. The axons from the ganglion cells converge at the optic disc to form optic nerve which enters the cranial cavity through the optic foramen. At the optic disc these axons acquire a myelin coat from oligodendrocytes of the CNS.
4. The optic chiasm is formed by decussating fibers, which originates from the nasal half of the retina, fibers from the temporal retina project ipsilaterally. The optic tract lies beyond the chiasm and carries fibers from the temporal part of the ipsilateral retina and fibers from nasal part of the contra lateral retina. Since visual stimuli in the left half of the visual field falls on the nasal half of the let retina and the temporal half of the right retina, the left half of the visual field is projected to the right hemisphere. Thus, each hemisphere receives visual input from the contralateral visual field.
5. the majority of fibers in the optic tract terminates in the ipsilateral lateral geniculate body (LGB) while some fibers continue beyond the LGB to terminate on cells in the superior colliculi and pretectal area. These latter terminations are important for visual reflexes.
6. the lateral geniculate body is a laminated structure which receives input from the optic tract and gives rise to axons which terminate on cells in the primary visual cortex of occipital lobe. The pathway from LGB to the sriate cortex is the visual radiation or geniculcalcarine tract. the visual radiation consists superior and inferior fibers a)superior fibers carry input from the upper retina b) inferior fibers carry inputs from the lower retina
C- THE VISUAL CORTEX
1. the primary
1. Light must pass through the cornea, aqueous humor, lens and vitreous humor before reaching the retina. It must then pass through the inner layers of the retina to reach the photoreceptive layer of rods and cones.
2. When the photoreceptors are stimulated they transmit impulses to the bipolar cells that project to the ganglion cells of retina.
3. The axons from the ganglion cells converge at the optic disc to form optic nerve which enters the cranial cavity through the optic foramen. At the optic disc these axons acquire a myelin coat from oligodendrocytes of the CNS.
4. The optic chiasm is formed by decussating fibers, which originates from the nasal half of the retina, fibers from the temporal retina project ipsilaterally. The optic tract lies beyond the chiasm and carries fibers from the temporal part of the ipsilateral retina and fibers from nasal part of the contra lateral retina. Since visual stimuli in the left half of the visual field falls on the nasal half of the let retina and the temporal half of the right retina, the left half of the visual field is projected to the right hemisphere. Thus, each hemisphere receives visual input from the contralateral visual field.
5. the majority of fibers in the optic tract terminates in the ipsilateral lateral geniculate body (LGB) while some fibers continue beyond the LGB to terminate on cells in the superior colliculi and pretectal area. These latter terminations are important for visual reflexes.
6. the lateral geniculate body is a laminated structure which receives input from the optic tract and gives rise to axons which terminate on cells in the primary visual cortex of occipital lobe. The pathway from LGB to the sriate cortex is the visual radiation or geniculcalcarine tract. the visual radiation consists superior and inferior fibers a)superior fibers carry input from the upper retina b) inferior fibers carry inputs from the lower retina
C- THE VISUAL CORTEX
1. the primary