Vision Flashcards
What 3 things are part of the uveal tract?
1) choroid
2) ciliary body
3) iris
The ______ is part of the sclera.
cornea
The retina contains ______
neurons
Describe the choroid.
largest, capillary, pigment epithelium
The ciliary body has both muscular & vascular components that go around what?
the lens
How do the iris muscles work?
muscles with opposing functions for pupil size
the anterior and posterior chambers of the eye are for what?
rate of production/drainage (glaucoma)
the vitreous humor deals with what?
shape & housekeeping functions (floaters
Normal vision requires that the optical media of the eye be ________
transparent
Where do you generate a focused image?
on the surface of the retina
What contributes to most of the necessary refraction when generating a focused image?
the cornea
What has more refraction power, the lens or cornea?
cornea
What contributes to the clarity of images on the retina?
adjustments in the size of the pupil
When looking at something far away, what muscles are relaxed?
ciliary muscle (and tension in zonule fibers, which flattens the lens)
What is a blind spot called?
scotoma
where is the optic disk located?
it is an area within the retinal surface
what does the optic disk measure?
intercranial pressure
What does macula lutea do?
It is the part of the retina that is responsible for sharp, detailed central vision
What do horizontal cells enable?
lateral interactions between photoreceptors and bipolar cells
What do horizontal cells maintain?
the visual system’s sensitivity to contrast, over a wide range of light intensities (luminance)
What are different subclasses of amacrine cells thought to do?
make distinct contributions to visual function (modulation of the visual info)
What is the house of the photoreceptors?
the pigment epithelium
what is pigment epithelium involved in?
1) the shedding –> phagocytosis of the outer clump of disks
2) regeneration of the photopigment
What happens in terms of APs during phototransduciton?
photoreceptors do not exhibit APs
What does the light activation in phototransduction cause?
a graded change in membrane potential
What happens when light is introduced to a rod?
the Na+ influx is reduced (Na cannot go through the channel into the cell)
Are the rods hyperpolarized or depolarized when it is dark?
depolarized
Are the rods hyperpolarized or depolarized when it is light?
hyperpolarization
When there is light, the retinals change from _____ to _____
cis to trans
What does IRBP mean?
inter photoreceptor retinoid binding protein
The magnitude of the phototransduction amplification varies with the prevailing level of what?
illumination
When are photoreceptors most sensitive to light?
at lower levels of illumination
As levels of illumination increase, sensitivity _____, preventing the receptors from saturating.
decreases
Light-induced closure of the Ca2+ cannels leads to what?
a net decrease in the internal Ca2+ concentration that triggers a number of changes in the phototransduction cascade (which will reduce the sensitivity of the receptor to light)
What is the ratio of cone connections?
1:1
What is the ratio of rod connections?
1 rod bipolar cell : 15-30 rods
Why are rods more sensitive than cones?
1 rod activates several other rods
What is the cone system specialized for?
acuity at the expense of sensivity
The rod system has very low ____ _____ but is extremely sensitive to light.
spatial resolution
In the scotopic visual function, what is activated?
only rods
In the mesopic visual function, what is activated?
only cones
In the photopic visual function, what is activated?
both cones and rods
Rods are mainly used in _____ environments.
dark
Cones are only used in ______ environments.
bright
What is tritanopia?
blue/yellow color blindness
How many photopigments do rods contain?
1
How many photopigments do cones contain?
3
What are the 3 types of cones?
1) blue (short)
2) green (medium)
3) red (long)
Each ganglionic cell responds to the stimulation of what?
a cell’s receptive field
what is a cell’s receptive field?
a small circular patch of the retina
What are the two classes of ganglion cells?
ON-center and OFF-center
What do ON-center cells increase?
increase the discharge rate to luminance increments in the receptive field center
What do OFF-center cells increase?
increase their discharge rate to luminance decrements in the receptive field center
The selective response of ON- and OFF-center bipolar cells to light increments and decrements is explained by the fact that they express what?
different types of glutamate receptors
Increases in background level of illumination are accompanied by ____________ such that greater stimulus intensities are required to achieve the same discharge rate (amacrine cells)
adaptive shifts in the ganglion cell’s operating range
What are ganglion cells sensitive to?
differences between the level of illumination that falls on the receptive field center and the level of illumination that falls on the surround
Response of an ______-center ganglion cell to the increase in the size of a spot of light placed in the receptive field center
ON
As the spot increases in size to fill the center, the response of the ganglion cell ________. As it extends into the receptive field surround, the response of the ganglion cell _________.
increases ; decreases
Because of their antagonistic surrounds, most ganglion cells respond how?
much more vigorously to small spots of light confined to their receptive field centers
what does hypothalamus regulate?
regulation of circadian rhythms
What is the function of pretectum?
reflex control of pupil and lens
what is the function of the superior colliculus?
orienting the movements of head and eyes
What is the pupillary light reflex?
a bilateral projection from the retina to the pretctum
What contains the preganglionic parasympathetic neurons that send their axons via the oculomotor nerve to terminate in which neurons in the ciliary ganglion which innervate the constrictor muscle in the iris.
the edinger-westphal nucleus
What provides an important diagnostic tool that allows the physician to test the integrity of the visual sensory apparatus, the motor outflow to the pupillary muscles, and the central pathways that mediate the reflex.
the pupillary reflex
Lateral visual field will go to the _____ retina
nasal
Temporal retina will associate with the ______ visual field.
right
Where is the upper visual field represented?
below the calcarine sulcus
The lower visual field is represented where?
above the calcarine
Where is the fovea represented?
in the posterior part of the striate cortex
More peripheral regions of the retina are represented progressively more ______ parts of the striate cortex.
anterior
What do neurons in the ________ ______ ______ respond selectively to oriented edges.
primary visual cortex
What do neurons in the primary visual cortex typically respond vigorously to?
a bar of light oriented at a particular angle (and less strongly to other orientations)
Retinohypothalamic tract is part of what?
circadian system
Photic information to the suprachiasmatic nucleus (SCN) is transmitted from the retina via the _____________.
retinohypothalamic tract (RHT)
