Flashcards in Chapter 12 - Central Visual Pathways Deck (52):
Ganglion cell axons exit the retina through ..
The optic disc.
Ganglion cell axons exit the retina through the optic disc, where they bundle together to form..
the optic nerve.
Axons in the optic nerve run a straight course to ..
the optic chiasm.
In one sentence, what happens in the optic chiasm?
In humans, about 60% of the optic nerve fibers cross in the chiasm.
Where is the optic chiasm?
At the base of the diencephalon.
From the optic chiasm, where do they fibers go?
Toward the thalamus and midbrain.
What is the name of the optic nerve fibers leaving the optic chiasm?
The ganglion cell axons in the optic tract reach a number of structures in the diencephalon and midbrain. The major target in the diencephalon is..
the dorsal lateral geniculate nucleus of the thalamus.
From the lateral geniculate nucleus, visual information travels towards the cerebral cortex via the ..
internal capsule, or the optic radiation.
The axons that travel along the internal capsule terminate in ..
The primary visual cortex (V1).
The primary visual cortex is also called..
the striate cortex.
The ganglion cell axons in the optic tract reach a number of structures in the diencephalon and midbrain. One target that is not the LGN is..
Pretectum: a collection of neurons that lies between the thalamus and the midbrain.
The pretectum is mostly known for..
The pretectum, a collection of neurons that lies between the thalamus and the midbrain, is mostly known as the primary coordinating center for the pupillary light reflex.
What is the pupillary light reflex?
The pretectum-coordinated reflex that is responsible for the reduction in the diameter of the pupil that occurs when sufficient light falls on the retina.
The pretectum receives its innervation from the ganglion cell axons of the optic tract, and does, in turn, project to..
The Edinger-Westphal nucleus.
What is the Edinger-Westphal nucleus?
A small group of nerve cells that lies close to the nucleus of the oculomotor nerve (cranial nerve III) in the midbrain. It receives its innervation from the pretectum.
How is the Edinger-Westphal nucleus connected to the pupillary light reflex?
It contains the neurons that send their axons via the oculomotor nerve to terminate on neurons in the ciliary ganglion. The ciliary ganglion neurons innervate the constrictor muscle in the iris, which decreases the diameter of the pupil.
Retinal ganglion cell axons travel to 4 targets you need to remember. Which and where?
1. Dorsal lateral geniculate nucleus of the thalamus
2. The pretectum between the thalamus and midbrain.
3. The suprachiasmatic nucleus of the hypothalamus.
4. The superior colliculus on the dorsal surface of the midbrain.
Animals that have completely lost form vision still are able to maintain normal circadian rhythms. Why?
The light-information that is used for the maintenance of circadian rhythm by the hypothalamus stems from specialized photoreceptors that are different from the rods and cones used for vision.
The informaton from the temporal retina runs ipsilaterally or contralaterally?
The informaton from the nasal retina runs ipsilaterally or contralaterally?
Why can we, by an analysis of visual field, with relative precision, find the site of neurological damage?
Because the spatial relationships in the retinas are maintained in central visual structures.
Relatively large visual field deficits are called..
Relatively small visual field deficits are called...
Damage to the retina or to one of the optic nerves before it reaches the optic chiasm results in a loss of vision that is..
limited to the eye or origin.
Damage in the region of the chiasm - or more centrally - results in specific types of deficits that involve the visual fields of which eye?
What is a homonymous hemianopsia?
It is a damage to the visual system that presents itself as a complete loss of vision in the affected region of the binocular visual field. It is caused by lesions in the optic tract.
Damage to middle portion of the optic chiasm results in what types of visual deficits?
The middle portion of the optic chiasm has the nerve fibers that cross over. The resulting loss of vision is confined to the temporal visual field of each eye, and is known as heteronomous hemianopsia.
What is Meyer's loop?
Meyer's loop is a branch of the optic radiation (the pathway from the LGN to the striate cortex)
Lesions in Meyer's loop result in what type of visual deficiency?
A loss of a quadrant of the visual field.
What is the unexplained phenomenon of macular sparing?
Injury to central visual structures can lead to this phenomenon: the loss of vision throughout wide areas of the visual field, with the exception of foveal vision.
David Hubel and Torsten Wiesel showed in their pioneering studies that visual cortex neurons were not very stimulated by small spots of light/dark on the retina. They responded the most to..
light-dark bars or edges, and only if the bars were presented at a particular range of orientations within the cell's receptive field.
A neuron in the visual cortex can be described as having a preferred orientation. What is meant by this?
The responses of cortical neurons are tuned to the orientation of edges. The orientation to which a cell is most responsive is referred to as the neuron's "preferred orientation".
Prefered or preferred?
By convention, neocortex is divided into how many cellular layers?
Where do the axons from the geniculate neurons terminate?
The axons of geniculate neurons terminate in alternating eye-specific ocular dominance columns.
What is binocular disparity?
The disparity between the information about an object when it comes from both eyes. Since they look at the world from slightly different angles, the image that is the basis of the later processing is slightly off. This creates depth.
Some neurons in the striate cortex respond strongly to stimuli that fall on non-corresponding parts of the retinas. Three classes of neurons are involved. Which?
Far cells, near cells and tuned zero.
What are far cells?
Far cells are neurons in the striate cortex that respond maximally to the disparity caused by objects beyond the plane of fixation.
What are near cells?
Near cells are neurons in the striate cortex that respond maximally to the disparity caused by objects in front of the plane of fixation.
What are tuned zero?
Tuned zero is a class of neurons in the striate cortex that respond selectively to points that lie on the plane of fixation.
The lateral geniculate nucleus has six layers. name them.
1-2 = Magnocellular layers.
3-6 = Parvocellular layers.
Between layers 1-6 lies the Koniocellular layers.
Which layer is dorsal to the other - Parvocellular / Magnocellular.
The parvocellular layers are dorsal to the magnocellular layers.
What is the main structural difference between the parvocellular and magnocellular layers?
The magnocellular layers are composed of large neurons, and the parvocellular layers are composed to small neurons.
Which type of cell in the lateral geniculate responds to color differences?
The cells of the parvocellular layers.
Damage to the magnocellular layer has what kinds of effects?
1. Little effect on visual acuity or color vision, but sharply reduces the ability to perceive rapidly changing stimuli.
Damage to the parvocellular layeres has what kinds of effects?
No effect on motion perception, but severely impacts visual acuity and color perception.
What is the function of the koniocellular layers?
Not clearly understood yet. Some aspects of color vision, especially information derived from short-wavelength-sensitive cones, may be transmitted via the K-cell rather than the P-cell pathway.
Where is the ventral stream?
The ventral stream leads from the striate cortex into the inferior part of the temporal lobe.
What is the dorsal stream?
The dorsal stream, which includes the middle temporal area, leads from striate cortex into the parietal lobe.
What is the function of the dorsal stream?
This system is thought to be responsible for spatial aspects of vision, such as the analysis of motion and positional relationships between objects in the visual scene.