Special Senses - Vision Flashcards
If an object is far away, light rays have_____ and _____ rays enter the eye. Does or does not need a lot of refraction.
diverged
only parallel
does not need a lot of refraction
If an object is near, light rays are_____. Need ________refaction to make the rays focus on the retina.
still diverging
more refraction
To focus an image on the retina, the eye uses
refraction
two sights of refraction
cornea and lens
cornea role in refraction
1st site of refraction
bends light the most of any structure (2/3 of the bending)
the amount of bending is fixed - we can’t control it
why do we need the variable refection provided by the lens
so we can see near things and farthings
Accommodation requires what 3 components
ciliary muscle, suspensory ligaments, the lens itself
Near vision requires ______ of the ciliary muscle
contraction.
when ciliary muscle contracts, the tension on suspensory ligaments ______ . The lens becomes _____
is released.
rounder
increasing the curvature of the lens ______ the refractive power of the lens
increases. allows the light rays from a nearby object to be bent sufficiently to bring them into focus on the retina
In young children, the lens can add ____ diopters, in the mid 20s, a loss of _____ results in a strength of ___ diopters. By 50s, the lens may be able to add only ____ diopters
20
elasticity
10
1
Far vision requires ______ of the ciliary muscle
relaxation
when the ciliary muscle relaxes, the tension on suspensory ligaments ______. The lens becomes _______.
increases
flat
decreased curvature of the lens _____ refractive power of the lens
decreases. if the object is far away, less bending of the parallel light rays is required, the lens needs to be flatter.
The near response includes (3)
contraction of ciliary muscles
convergence of eyes to point of focus
constriction of pupil
constriction of the pupil in the near response does what
reduces the opening for light to enter, eliminating some diverging light rays - this allows us to focus better.
In the retina, light moves from ____ to _____
the inner limiting membrane to the pigment epithelium through multiple layers of cells
in the retina there are multiple cell types (5)
photoreceptor cells bipolar cells ganglion cells horizontal cells amacrine cells
Light passes through all of the layers of cells (except RPE). as a result, there is
distortion of the image that the retina will take care of
Vertical pathway of the retina is composed of (3)
photoreceptor
bipolar cell
ganglion cell
The vertical pathway is the pathway for
relaying visual information to the brain
The circuit for the _____ seems to be the base for all vision
cones
photoreceptors have a constant release of ____
glutamate
in the dark - photoreceptor release of glutamate is _____
high
when a photon activates photoreceptor, release of glutamate is______
low (remember that light hyper polarizes the rods and cones)
Vertical pathway for cones
- light hits a photoreceptor
2. photoreceptor is hyperpolarized => decreased release of NT (glutamate) onto a bipolar cell
On-center bipolar cell
activation of photoreceptor (decrease glutamate to center of cell) in CENTER of bipolar cell’s receptive field causes DEPOLARIZATION of the bipolar cell.
activation of photoreceptor (decreased glutamate to periphery) in the SURROUNDING region causes HYPERPOLARIZATION of the bipolar cell
Off- center bipolar cell
activation of photoreceptor (decreased glutamate to periphery) in the SURROUNDING region causes DEPOLARIZATION of the bipolar cell
activation of photoreceptor (decreased glutamate to center of cell) in CENTER of bipolar cell;s receptive field causes HYPERPOLARIZATION of the bipolar cell
When a photoreceptor is activated, where does depolarization occur in an on center bipolar cell as compared to an off center bipolar cell>
the center
the periphery
if a photoreceptor activates an on center bipolar cell, what type of receptor are we thinking
metabotropic
if a photoreceptor activates an off center bipolar cell, what type of receptor are we thinning
AMPA
On-center bipolar cell mechanism
metabotropic receptor
NT binding the receptor (DARK) causes a DECREASE in cation influx
so… in the dark, the on-center cell is hyper polarized
with light, photoreceptor releases LESS glutamate, so cation current increases and the on center cell is depolarized
Off-center bipolar cell mechanism
AMPA receptor
NT binding the receptor (DARK) causes an INCREASE in cation influx
so… in the dark, the off-center cell is depolarized
with light, photoreceptor releases LESS glutamate, so cation current decreases and the off center cell is hyper polarized
Ganglion cells are also On-center and off-center based on
whatever their connection bipolar cell is
When bipolar cells are depolarized, they release what NT
glutamate
bipolar cells, when depolarized, release glutamate onto what cells
ganglion cells.
Ganglion cell axons become
the fibers of the optic nerve
The first place in the eye we see true action potentials is
the ganglion cells.
Ganglion cells rely on _____ as NT
glutamate
Describe the vertical pathway for rods
many rods converge on one ON-center bipolar cell
bipolar cell synapses on an A11 amacrine cell
A11 amacrine cell synapses on a cone ON-center bipolar cell
the cone on-center bipolar cell activates a ganglion cell
Rods do vision in ______ situations
low light
need many rods to converge on a _______. WHy>
bipolar cell. to increase our chances of seeing what we need to see.
Role of on and off center cells
these two types of cells help us increase the ability to detect edges and sharpen our vision
on center cells tell us
where something is
off center cells tell us
where something ends.
amacrine cells and horizontal cells
provide inhibitory signals that modify the activity of neighboring photoreceptors, bipolar cells or ganglion cells
Action potentials occur in what cells
ganglion cells
axons from ganglion cells will become
fibers of the optic nerves
the retina from each eye sees ______ visual fields
two different
The Left temporal retina is activated by light coming from
the right visual field
the right nasal retina is activated by light coming from
the right visual field
the right temporal retina is activated by light coming from
the left visual field
the left nasal retina is activated by light coming from
the left visual field
at the _____ the axons from the ______ retina on each side will cross and join the axons from the _____retina
optic chiasm
nasal retina
temporal retina
Crossing at the optic chiasm allows what
all of the information from one visual field to be sent to the same part of the brain (the side opposite the visual field)
after the axons cross at the optic chiasm, they synapse where
lateral geniculate body
cells in the LGN are of what type
on and off center as well
functions of the LGN (4)
- control motions of the eyes - so they converge on the desired point of interest
- control focusing - so that the image we are interested in is in the best focus possible
- identify major elements within our visual image - send that info to the cortex
- identify motion
The neocortex is divided into ____ layers of cells
6
Primary visual cortex =
V1
layers 1, 2, 3 allow
networking between V1 and other parts of the cortex
layer 4
receives inputs from the LGN
Layers 5 and 6
send information back to the LGN
cortex is divided from a functional standpoint into
columns
each column does _____
neighboring columns have _____
a different job
related jobs
There are a lot of columns in V1 that receive input from photoreceptors in the macula
in part bc that is the place where receptor density is the greatest
peripheral regions of the retina have much less area in V1 devoted to them
few receptors, many of which converge onto the same bipolar cells
MAJOR JOB OF V1
identify edges/contours of the components in visual image
MAJOR JOB of V2
identify disparities in the visual images presented by the two eyes - gives us depth perception
Color vision in V1 is done by
blobs
accurate color detection depends on input from
all three sets of cones
_____ kinds of cones are triggered by any bright light
all three kinds of cones, because of the overlap in the sensitivities of opsins. certain types will just be activated more
how does the brain arrive at color perception
uses the overlapping activity of the opsins
MAJOR JOB of V4
complete processing of the color inputs
without higher processing of the visual image, we could reconstruct the visual image but not
name the image copy the image aim at the object in the image recognize husband/wife/father/mother we must rely on other areas of the cortex to interpret why the primary visual cortex and associated areas have done so far
Dorsal pathway - think
motor
Dorsal pathway - explained
the dorsal pathway leaving the occipital cortex relays information to the motor cotices and enables us to complete motor acts based on visual input - allows you to play catch
Ventral pathway - think
recognition
Ventral pathway - explained
the ventral pathway relays visual info to areas of the brain involved in higher processing of sensory inputs. The integration of visual input with other sensory input allows us to use that visual image to accomplish higher order functions, including naming the object and copying the object
copying an object and naming/recognizing it are _____functions. damage to the temporal lobe can
separate
selectively impair one without hindering the other
Similar or related objects are all coded for in
localized regions of the temporal lobe
there is a specialized area for _________ (implications in autism)
recognizing human faces.
