Special Senses Lecture 2 Flashcards
What does a negative mean in front of the Sphere number?
It means you are shortsighted
What does a Positive Sphere indicate?
Hyperopia
What does the Cylinder column represent?
Whether there is an astigmatism or not
What does the Axis on a prescription represent?
The degree of Astigmatism
What does the Add column indicate?
The strength of the sphere due to presbyopia
What does the Prism indicate?
The shift necessary to correct misalignment of the two eyes due to muscular imbalance
What is the Fovea?
The place on the retina with the greatest visual acuity
How is the Retina built backwards?
The first layer of cells that the light strikes in the retina are cells of the final common pathway (ganglion cells)
What do Rods see?
Vision in shades of grey
What do cones see?
Color vision
What is the relative sensitivity of rods and cones?
Rods are high sensitivity while cones are low sensitivity and require more light
What is the Relative Acuity of rods and cones?
Rods have low acuity pathways while cones have high acuity pathways
What is the relative Convergence of rods and cones?
There is much convergence in retinal pathways of rods and little convergence in retinal pathways cones
Where are cones concentrated?
In the fovea
Where are rods numerous in?
The retinal periphery
What is the activity of rod cells in the dark?
They are turned on and not sending impulses to the ganglion
What are the steps taken to keep rod cells on in the dark?
A high concentration of cGMP binds to sodium channels allowing them to remain open and sodium to enter the cell. This causes the membrane to be depolarized and calcium channels in the synaptic terminal to open and release glutamate which binds to ganglion cells and inhibits them
How does Glutamate affect ganglion cells in the eye?
It inhibits them preventing signals from occurring
How are rods activated when light hits the eye?
- Light changes the conformation of retinal in rhodopsin to all trans retinal causing rhodopsin to change shape
- The alpha subunit of Rhodopsin binds to Phosphodiesterase (PDE)
- PDE converts cGMP to GMP causing it to unbind from sodium channels
- Calcium channels close and glutamate stops being released
- Disinhibiting ganglion
What is Rhodopsin made of?
Retinal and Protein, opsin
What lies adjacent to photoreceptors?
Retinal, Pigment, Epithelium
What does Retinal Pigment Epithelium do?
- Absorbs some of the light not absorbed by photoreceptors
* Transports nutrients and ions to the photoreceptors a
What is required for regeneration of 11-cis-retinal?
The RPE
Why is it necessary for RPE to to absorb light not absorbed by photoreceptors?
To prevent light scatter which could reduce visual acuity
What occurs in the photoreceptors daily renewal process?
10% of their volume is shed and phagocytosed by the RPE
What occurs after trans-Retinal is used?
It is reduced to trans-retinol (aldehyde) and exits the cell and is reconverted to to 11-cis-retinol and then 11-cis-retinol in the RPE
What is the Receptive Field?
An area on the retina which when stimulated causes a change in the output of either a particular bipolar cell or ganglion cell
What occurs when light strikes an on center ganglion field in the center?
Ganglion cells are excited
What occurs when light strikes outside the center of an on center receptive field?
The ganglion will not be excited
What happens when light strikes an off center field off of the center?
Ganglion are excited
What happens when light strikes an off center field on center?
Ganglion cells are not excited
What causes the difference in response between On and Off channels?
- Off bipolar cells express AMPA and kainate type receptors which are cation channels opened by glutamate and hyperpolarize in response to light
- On bipolar cells express mGLuR6 metabotropic receptors that uses second messengers which when glutamate binds to the receptor causes closing of the cation channels and depolarizing TRPM1
Where do On-center channels have their acon terminals?
In the inner half of the inner plexiform layer
Where do Off-center channels have their terminals?
In the outer half of the inner plexiform layer
What kind of receptors do off bipolar cells have?
AMPA kainate receptors
What are AMPA and Kainate type receptors?
Cation channels in off-center bipolar cells that are opened by glutamate
What type of receptors do On-center cells express?
Metabotropic mGluR6 receptors
What are mGluR6 receptors?
Receptors expressed by on-center bipolar cells that when glutamate bind close cation channels
