Physiology of Visual System Flashcards
(35 cards)
1
Q
- The eye uses _ to focus image on retina
- Which site accounts for most?
- When the lens is rounder is there more or less?
- When the lens is flatter is there more or less?
A
- Refraction
- Cornea (also first site)
- Rounder lens=more refraction
- Flatter lens=less refraction
2
Q
- The curvature of the lens requires what muscle and ligaments?
- Increasing curvature occurs with contraction or relaxation of these muscle/ligaments?
- Decreasing curvature occurs with contraction or relaxation of these muscles/ligaments?
A
- Ciliary m and suspensory L
- Increasing curvature
- Ciliary m contracts
- Suspensory L relaxes
- Decreasing curvature
- Ciliary m relaxes
- Suspensory L contracts
3
Q
- Describe the near vision response and how it works in the eye
A
- Contraction of ciliary muscles
- Convergence of eyes to point of focus
- Constriction of pupil
- Reduces opening for light to enter
- Eliminates diverging rays
- Allows better focus
4
Q
- Describe the far vision response and how it works in the eye
A
- Ciliary muscles relax
- Suspensory ligament pulls on lens
- Lens becomes flatter to focus on distant objects
5
Q
- What are the 5 neuron types in the retina?
- Where do electrical signals begin?
A
- Vertically oriented
- Receptor cells (rods and cones)
- Bipolar cells
- Ganglion cells
- MG subtype of ganglion cells
- Horizontally oriented cells
- Horizontal cells
- Amacrine cells
6
Q
- Rod system
A
- Lots of convergence from many rods onto one ganglion cell
- Allows rods to operate in dim light
- Sacrifices acuity to gain sensitivity
7
Q
- Cone system
A
- Less convergence
- Maximal acuity
8
Q
- The highest density of cones is located in the _ whereas the highest density of rods are _
A
- Fovea
- Periphery (20 deg away from fovea)
9
Q
- Rods and cones constantly release what NTX?
A
- Glutamate
10
Q
- Release of glutamate is highest when it is _
- Release of glutamate is lowest when it is _
A
- Dark
- Light
11
Q
- Activation of bipolar cell by a cone receptor in the light (just as an example)
A
- Photons will stimulate cone receptor
- Photoreceptor hyperpolarizes
- Less glutamate is released onto the bipolar cell
12
Q
- On center bipolar cells /Depolarizing Bipolars
A
- Activation of a photoreceptor in the center of this bipolar cell’s receptive field will cause depolarization
- Activation in the periphery of this cell causes hyperpolarization
13
Q
- Off center bipolar cells /Hyperpolarizing Bipolars
A
- Activation in center of this bipolar cell will cause hyperpolarization
- Activation in periphery of this bipolar cell will cause depolarization
14
Q
- The glutamate receptor in a depolarizing bipolar/on center cell is a _ receptor
- The glutamate receptor in a hyperpolarizing bipolar/off center cell is a _ receptor
A
- GPCR (Gi)-sign change occurs
- non-NMDA (AMPA and Kainate)-no sign change
15
Q
- Example:
- Activation of an on-center/depolarizing bipolar by a cone receptor in DARK
A
- Dark-more glutamate
- Glutamate will activate GPCR (Gi) on ON-Center Bipolar Cell
- Results in decrease in cation influx in bipolar cell
- Hyperpolarization of the cell
16
Q
- Example
- Activation of an on-center/depolarizing bipolar cell by a cone photoreceptor in the light
A
- Light-less glutamate release
- Light decreases presence of glutamate
- Less glutamate around
- Less activation of metabotropic receptor (GPCR-Gi) of on-center cell
- Less Gi signaling
- Increase in cation influs into bipolar cell
- Depolarization of cell
17
Q
- Example:
- Activation of an off-center bipolar cell by a cone photoreceptor in the dark
A
- Dark-more glutamate
- More glutamate present (cuz we are in the dark)
- Glutamate activates AMPA receptor on off center cell
- Increase cation influx
- Depolarizaton of the cell
18
Q
- Example
- Activation of an off center bipolar cell by a cone photoreceptor in the light
A
- Light-less glutamate
- Light decreases presence of glutamate
- Less glutamate around
- Less activation of AMPA receptor of off-center bipolar cell
- Decrease in cation influx into bipolar cell
- Hyperpolarization of the cell
19
Q
_ axons become fibers of the optic nerve
A
- Ganglion cell
20
Q
Ganglion cells release what NTX in the cortex?
A
- Glutamate
21
Q
- Activation of a bipolar cell by rod photoreceptors
A
- Rods signal vision in low light situations
- Many rods converge onto one on-center bipolar cell
- COnnects to a rod-bipolar cell and a rod amacrine cell (use glycine or GABA to inhibit cone pathway)

22
Q
- What does the on-center system tell us?
- What does the off-center system tell us?
- What do the amacrine and horizontal cells do?
A
- On center system tells us
- Where something is
- Off center system tells us
- Where something ends
- Horizontal/Amacrine cells release GABA/Glycine to inhibit nearby cells in retina
23
Q
- Direct targets of the retina
A
- LGB (Lateral Geniculate Body)
- Superior colliculus
- Pretectum
- Hypothalamus
- AON (Accessory optic nuclei)
- Pulvinar
24
Q
- Properties and functions of the LGB
A
- Signals from two eyes kept apart
- Functions
- Control motions of eyes to converge on point of interest
- COntrol focus of eyes based on distance
- Determine position of objects to map them in space
- Detect movement relative to an object
- Relay cells via optic radiations to visual cortex on IPSILATERAL side
25
* What layer of the primary visual cortex (V1) receives input from the LGB?
* What layers of V1 send outputs? Where do these outputs go?
* IV
* V and VI
* LGB
* Thalamus
* Subcortical regions
26
* Ocular dominance columns
* Where are they located?
* What do they do?
* Located in V1 (Primary Visual Cortex)
* Columns spand all 6 layers
* Preferentially respond to input from one eye or the other (hence the name ocular dominance)
27
* Orientation columns
* Where are they located?
* What is their function?
* Also located in V1
* Columns that span all 6 layers of V1
* Excited by visual line stimuli of varying angles
* Oriented perpendicular to the cortical surface
28
* Blobs
* Where are they located?
* What is their function?
* Located in V1
* Span all 6 layers of V1
* Sensitive to color

29
* Major job of V1
* Identify edges and contours of objects

30
* Function of V2
* Depth perception

31
* Visual cortex (V3a) function
* Identification of motion

32
* Function of V4 area of visual cortex
* Complete processing of color inputs

33
***Dorsal pathway (Where pathway)***
* From primary visual cortex to parietal/frontal cortex
* Parimary path associating vision with movement
* Completes motor acts based on visual input
* Passes thru V3

34
* ***Ventral Pathway (What Pathway)***
* From primary visual cortex to inferior temporal cortex
* Involved in interpreting images (recognizing or copying shapes, forms, faces) and complex patterns
Aside:
Copying/naming objects are separate functions. Damage to one is possible without damaging the other
Facial recognition is in a specialized area

35
MG Ganglion Cells
* Light, via melanopsin causes changes in Ca2+ levels in MG cells
* non-image forming but sends this information to the hypothalamus (suprachiasmatic nucleus)
* AIDS w. CIRCADIAN RHYTHMS
