Chapter 10

Chapter 10 - Chapter 10 Retinofugal Projection Neural...

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Chapter 10 Retinofugal Projection Neural pathway that leaves the eye Optic nerve, optic chiasm and optic tract o Chiasm lies at base of brain, just anterior to where pituitary gland dangles down o Decussation – crossing of a fiber bundle from one side to the other o Axons of the retinofugal projections form the optic tracts, which run just under the pia along the lateral surfaces of the diencephalon Right and left visual hemifields o Binocular visual field is field seen by both eyes o Optic chiasm leads to left visual hemifield ‘viewed’ by right hemisphere and vice versa Targets of the optic tract o Most optic tract axons innervate the lateral geniculate nucleus (LGN) of the dorsal thalamus o Neurons in LGN give rise to axons that project to the primary visual cortex o Direct projections to part of the midbrain, the pretectum, control the size of the pupil and certain types of eye movement o 10% of the ganglion cells in the retina project to a part of the midbrain tectum called the superior colliculus called optic tectum in nonmammalian vertebrate groups LGN 6 layers Right LGN receives information about left visual field The left visual field is viewed by both the nasal left retina and the temporal right retina Ventral layers are magnocellular LGN layers Dorsal layers are parvocellular LGN layers Numerous tiny neurons also lie just ventral to each layer called the koniocellular layers which receive input from the nonM-nonP type cells Magnocellular LGN neurons have relatively large center-surround receptive fields, respond to stimulation of their receptive field centers with a transient burst of action potentials and are insensitive to differences in wavelength o Like M-type ganglion cells Parvocellular LGN cells, like p-type retinal ganglion cells, have relatively small center-surround receptive fields and respond to stimulation of their receptive field centers with a sustained increase in the frequency of action potentials Receptive fields in the koniocellular layers are center-surround and have either dark/light or color opponency Within all layers of the LGN, the neurons are activated by only one eye and ON- center and OFF-center cells are intermixed Anatomy of the Striate cortex
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Primary visual cortex is Brodmann’s area 17 and is located in the occipital lobe of the primate brain o other terms used to describe the primary visual cortex are v1 and striate cortex Retinotopy o Organization whereby neighboring cells in the retina feed information to neighboring places in their target structures- in this case the LGN and he striate cortex o 2-d surface of the retina is mapped onto the two-dimensional surface of the subsequent structures o 3 important points too remember about retinotopy Mapping of the visual field onto a retinotopically organized structure is often distorted striate cortex: central few degrees of the visual field are overrepresented or magnified in the retinotopic
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Chapter 10 - Chapter 10 Retinofugal Projection Neural...

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