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61 Cards in this Set

  • Front
  • Back
What does the visual system provide?
(1) sight - recognition and location of objects

(2) control of eye function and movement

(3) detection of season and time of day

(4) information used in postural and limb movement control
What is the retina?
It is located at the back of the eye. It contains photoreceptors specialized to convert light energy into neural activity
What is the Lateral geniculate nucleus?
The LGN is the first synaptic relay in the pathway that serves visual perception. This cell group is located in the dorsal thalamus

From the LGN, visual information ascends to the cerebral cortex, where it is interpreted and remembered
What is a wavelength?
the distance between successive peaks or troughs
What is frequency?
the number of waves per second
What is amplitude?
the difference between wave trough and peak
What is refraction?
the bending of light rays that can occur when they travel from one transparent medium to another.
What is the pupil?
It is the opening that allows light to enter the eye and reach the retina.
Describe the Iris
the iris surrounds the pupil. it contains two muscles that can vary the size of the pupil. one muscle makes it smaller when it contracts, the other makes it larger.

it regulates aperture by constricting or dilating
What is the cornea?
it is the glassy transparent external surface of the eye
What is the sclera?
it is the opaque, fibrous material that forms the tough wall of the eyeball. it is continuous with the cornea
What is the fovea?
Is a tiny depressed region in the macula. it contains only cones, and at a high density

Its structural specialization maximizes visual acuity by pushing aside other cells that might scatter light and blur the image
What nourishes the cornea?
aqueous humor.
Describe the lens.
The lens is located behind the iris. it is suspended by ligaments called zonule fibers that are attached to the ciliary muscles

The lens divides the eye into two compartments.
What do zonule fibers do?
the pull on and flatten the lens
What is the function ciliary muscles?
they slacken the zonule fibers. this in turn changes the shape of the lens
Define accommodation.
it is the additional focusing power provided by the lens of objects that are nearby
What is the Pupillary light reflex?
it involves connections between the retina and neurons in the brain stem that control the msucles that constrict the pupils.

an interesting property of this reflex is that it is consensual; shining a light into only one eye causes the constriction of the pupils of both eyes

It is controlled in the pretectal area, just anterior to the superior collicullius
What is the affect of a small pupil?
it makes distant objects clearer (or less out of focus) as the eye accommodates to near objects
What is the pretectal area?
Through reciprocal bilateral projections to the retina, it is primarily involved in mediating behavioral responses to acute changes in ambient light such as the pupillary light reflex, the optokinetic reflex, the accommodation reflex, and temporary changes to the circadian rhythm

the pretectum is located directly anterior to the superior colliculus and posterior to the thalamus
What are cones?
photoreceptors that enable us to see in the daylight. They are responsible for color vision and sharp images

prevail at the center of the retina - especially at the fovea where they are densely position
What are rods?
photoreceptors that are sensitive to light. They make vision possible in low light or dark. They are insensitive to color and have a low resolution

They dominate the periphery
What is visual acuity?
The ability of the eye to distinguish two nearby points
What is the Trichromatic Theory of Color Vision?
This theory states that three receptors in the retina of the eye are responsible for the perception of color by the brain. Each receptor is sensitive to a single color: red, green or blue. The combination of these three colors can form any visible color in the spectrum.

Each type of cone contains a different type of opsin, which absorbs light different
What is opsin?
It is a 7-transmembrane region G-protein-couple receptor. Opsin mediates the conversion of a photon of light into an electrochemical signal, the first step in the visual transduction cascade
What is transducin?
It is G-protein that activates the effector enzyme phosphodiesterase (PDE) during bleaching
What is phosphodiesterase?
it breaks down cGMP that is normally present in te cytoplasm of the rod (in the dark). The reduction of cGMP causes the Na+ channels to close and the membrane to hyperpolarize.
What is an OFF bipolar cell?
a glutamate-gated cation ion channel that mediates a classical depolarizing ESPS from the influx of Na+

it responsds to light off (more glutamate)
What is an ON bipolar cell?
a g-protein-coupled receptor that response to glutamate by hyperpolarizing

it responds to light on (less glutamate)
What is the receptive field of a bipolar cell?
the area of retina that, when stimulated with light, changes cell's membrane potential. consist of two parts:

(1) a circular area of retina providing direct photoreceptor input (receptive field center)

(2) a surrounding area of retina providing input via horizontal cells (receptive field surround)
Which photoreceptor has more sensitivity to light?
Rods have a greater sensitivity because they are more convergent.

They have a greater number of disks and higher photopigment concentrations that make them over 1000 times more sensitive than cones
What is an M cell?
an M cell stands for magnocellular cell. They have large receptive fields, they conduct action potentials more rapidly in the optic nerve, and they are more sensitive to low-contrast stimuli.

They respond to stimulation of their receptive field centers with a transient burst of action potentials
What is a P cell?
P cell stands for parvoceullar cells. they are small cells that are sensitive to difference i the wavelength of light.

The majority of these color-sensitive neurons are called color-opponent cells, reflecting the fact that the response to one wavelength in the receptive field center is canceled by showing another wavelength in the receptive field surround.

Thus, color of the surround nullifies the response of the center.
What is Color-opponent cell?
a cell in the visual system with an excitatory response to wavelengths of light of one color and an inhibitory response to wavelengths of another color; the color pairs that cancel each other are red-green and blue-yellow
What is decussation?
the crossing of a fiber bundle from one side of the brain to the other
What are the optic nerve projections?
optic chiasm, optic tract, collaterals, and the thalamus (specifically the lateral geniculate nucleus)
What is binocular visual field?
optic nerve fibers cross in the optic chiasm, but not all, so that the left visual hemifield is viewed by the right hemisphere, and the right visual hemifield is viewed by the left hemisphere.
What are the projections of the optic tract?
Hypothalamus - biological rhythms

Pretectum - pupil size

Superior Colliculus - reflexive eye movements

Lateral Geniculate Nucleus (more about this in other FCs)
Where is the LGN located?
the dorsal thalamus
What are retinotopic maps?
They are distorted maps of the retina because visual space is not sampled uniformly by the cells in the retina.... this also occurs in the tectum
What are the retinotopic map layers of the contralateral eye?
layers 1,4,6
What are the retinotopic map layers of the ipsilateral eye?
layers 2,3,5
What retinotopic map layers consist of the M-cells?
1 and 2
What retinotopic map layers consist of P-cells?
3 through 6
What is the concept of parallel processing?
multiple streams of data analyzed at the same time independently
what is a corticofugal fiber?
nerve fibers conveying information away from the cortex.
What is the Brodmann's Area of the primary visual cortex?

What are other terms for this area?
17

other terms used to describe the promary visual cortex are V1 and striate cortex.
How many layers are in the visual cortex? Which level of cortex contains input?
There are 6 layers of the visual cortex. Inputs are in layer IV.
What is unique about layer IV?
Layer IV is broken up into an A, B, and C layers. And the C layer is further subdivided in to C-alpha and C-beta.
What are ocular dominance columns?
A region of striate cortex receiving information predominately from one eye
In what layers of cortex are M and P cells?
M cell are in the IVC-alpha layer and P cells are in the IVC-beta layer.
What are blobs?
blobs are pillars of cytochrome oxidase-rich neurons.

they receive direct LGN input from the koniocellular layers, P cell layers, and M cell layers.
What does it mean to have binocular receptive fields?
that the neurons have two receptive fields, one in the ipsilateral and one in the contralateral eye.
What is orientation selectivity?
the property of a cell in the visual system that responds to a limited range of stimulus orientations (vertical, perpendicular, etc)

orientation-selective neurons are thought to be specialized for the analysis of object shape.
What is direction selectivity?
these neurons are thought to be specialized for the analysis of object motion.
What are orientation columns?
a column of visual cortical neurons stretching from layer II to layer IV that responds best to the same stimulus orientation.
What are cortical modules?
they are 2 mm chunks of visual cortex with all orientation columns needed to analyze one spot in the visual field.
What is the dorsal stream?
serve the analysis of visual motion and the visual control of action.
What is the ventral stream?
involved in the perception of the visual world and the recognition of objects.
What is area MT?
an area of the neocortex, at the junction of the parietal and temporal lobes, that receives input from primary visual cortex and appears to be specialized for the processing of object motion; also called V5
What three roles are proposed for the dorsal stream?
(1) navigation - interpreting objects in peripheral vision that can tell direction & speed

(2) directing eye movements - moving eyes when sensing an object in the periphery

(3) Motion perception - interpreting moving objects