neurobio 916 ch 10 of Bear's book: the central visual system part 1 (retinofugal projection optic n
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what is the neural pathway that leaves the eye, beginning with the optic nerve, called?
the retinofugal projection
what occurs at the optic chiasm?
at the optic chiasm, axons originating in the nasal retinas cross from one side of the brain to the other.
what are the three components of the retinofugal projection?
optic nerve, optic chiasm, and optic tract
what does the term decussation refer to?
the crossing of a fiber bundle from one side of the brain to the other is called a decussation
the entire region of space that can be seen with both eyes looking straight ahead is known as...
the full visual field
if one was to divide the full visual field into two equal halves, what would the halves be called?
the left and right visual hemifields
what is the binocular visual field?
the region of space in which the central portion of both visual hemifields is viewed by both retinas
in what way do the nerve fibers cross in the optic chiasm? (what goes where?)
optic nerve fibers cross in the optic chiasm so that the left visual hemifield is viewed by the right hemisphere and the right visual hemifield is viewed by the left hemisphere
most of the optic tract axons innervate what structure?
the lateral geniculate nucleus of the dorsal thalamus
after info goes to the LGN, it is channeled where and through what structure?
it is channeled to the primary visual cortex by means of the optic radiation
some optic projections synapse directly with a part of the midbrain called the pretectum, which does what?
it controls the size of the pupil and certain types of eye movement.
about __% of the ganglion cells project to a part of the midbrain tectum called the ______ _______, which does what?
about 10% of the ganglion cells in the retina project to the superior colliculus. In the superior colliculus, a patch of neurons activated by a point of light, via indirect connections with motor neurons in the brain stem, commands eye and head movements to bring the image of this point in space onto the fovea.
what distinguishes the first and second layers of the LGN from the other layers? what is the name given to the first two layers? To the other layers? What is the basis of this difference?
layers 1 and 2 (the two more ventral layers) contain larger neurons and the four more dorsal layers contain smaller cells. The ventral layers are therefore called magnocellular LGN layers and the dorsal layers are called parvocellular LGN layers.
P-type ganglion cells in the retina project exclusively to the parvocellular LGN and M-type ganglion cells in the retina priject entirely to the magnocellular LGN
what are the layers tiny neurons that lie just ventral to each layer called? what is their function?
koniocellular layers. they receive input from the nonM-nonP types of retinal ganglion cells and also project to visual cortex.
true or false, in the LGN, info from both eyes is kept separate
how does the size of the of the visual receptive fields of LGN neurons compare to the receptive fields of the ganglion cells that feed them?
the visual receptive fields of LGN neurons are almost identical to those of the ganglion cells that feed them
the striate cortex (visual cortex) is divided into how many layers?
there are six layers (in the Brodmann's convention of numbering). However, if one was to divide some of these layers further, one would get 9 layers
How is layer IV divided?
it is divided into three sublayers, labeled IVA, IVB, and IVC. IVC is further divide dinto to two tiers called IVCα and IVCβ.
what are the two principal types of cells found in the striate cortex?
spiny stellate cells and pyramidal cell
what are spiny stellate cells and where are they found?
spiny stellate cells are small neurons with spine ocvered dendritedthat radiate out from the cell body. They are primarily in the two tiers of layer IVC. They only form local connections
what arepyramidal cells and where are they found?
outside layer IVC are many pyramidal cells. These neurons are also covered with spines and are characterized by a single thick apical dendrite that branches as it ascends toward the pia mater and by multiple basal dendrites that extend horizontally. pyramidal cells in one layer can have dendrites extending into other layers. Only pyramidal cells send axons out of the striate cortex to form connections with other parts of the brin.
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