Week 2 Flashcards
Transduction
The process of converting one type of energy into another.
Changing light energy into neural signals
Intrinsically photosensitive retinal ganglion cell
ipRGC
Visual receptor #3
- helps regulate circadian rhythms and pupillary reflex.
- has maintenance ability
Rods
Function similar to cones.
120 million in our eyes.
Peripheral retina has both rods and cones, but there are more rods than cones.
- more accustomed to low-light, detail vision, low spatial acuity
Cones
Function similar to rods.
6 million in our eyes.
Fovea contains only cones
Color vision, high spatial acuity
Two stage Dark Adaptation Curve
- stage 1 begins with rapid increase in sensitivity (3-4 min)
- the sensitivity levels off (7 - 10 min)
- Stage 2 shows increased sensitivity for another 20 - 30 mins. This is when the rods take over cones.
Experiment for cone adaptation
Test light falls directly on fovea - only simulates cones.
Results show that sensitivity increases 3 -4 mins and then levels off.
Experiment for rod adaptation
Must use a rod monochromatic person (born with no cone receptors)
Results show that sensitivity increases for about 20 - 30 mins and then levels off.
Why do rods and cones become more sensitive in the dark?
When retinal is isomerized (charges shape) it separates from the visual pigment (loss of retinal pigment and color = visual pigment bleaching)
And the darkness provides the opportunity to regenerate.
Isomerization
The process when a single photon of light is absorbed by a retinal molecule, causing the molecule to change shape.
How many visual pigment molecules need to go through isomerization t be detectable by a person?
** 7 ** of the 100 photons was absorbed by the light sensitive retinal molecule on the visual pigment.
100 to the eye - 50 reflected or absorbed - 50 reach retina - 7 absorbed by visual pigment
During transduction, photons of lights are absorbed among the discs in the ____ of the photoreceptor
Outer segment
The visual pigment molecule is a long protein strand called …
Opsin
Rhodopsin in rods
Photopsin in cones
The retinal
Only one location on the protein stand is reactive to light.
Reach visual pigment molecule has only 1 retinal
Enzyme cascade
1000s of chemical reactions leading to a change in receptor activity
- caused by imsomerization
Selig Hecht
Him and his colleagues wanted to find out how many visual pigment molecules need to go through isomerization to be detectable by a person.
Conclusion: it is unlikely fro more than one photon to reach a single receptor, activation of 7 rod receptors must make a test signal perceptible.
The specific part of the visual pigment that reacts to light, triggering the enzyme cascade in transduction, is the:
A. Opsin
B. Retinal
C. Disc
D. Outer segment
E. inner segment
B
Vision in daylight using cones is
Photopic
Vision at night using rods
Scotopic
Vision in between
Mesopic
Lens are more/less flexible and harder/softer as you age.
Less flexible; harder
AMD Age-related Macular Degeneration
- Fovea and macula are destroyed.
- Caused by interrupted supply of blood to the macula.
- Can’t see the center of a scene.
- Most common in older individuals
Wet AMD
(Less common)
The irregular growth of blood vessels which separates pigment epithelium away from back of retina
Dry AMD
Little protein deposits push out pigment epithelium and killing off the retina.
Retinas pigmentosa
Genetic disease that affects the receptors on the retina.
- rods are destroyed first.
- foveal cones can also be attacked.
Sever cases: result in blindness
No effective treatment, but onset may be delayed with vitamin A supplements.
Glaucoma
Damage to the optic nerve (where retinal ganglion cells leave the eye.)
It is most often caused by increased pressure in the eye, inhibiting blood flow to the optic nerve.
It can be gradual and hard to detect.
Blind spot
The place where optic nerve leaves the eye (also called optic disk)
We don’t notice it because:
- one eye covers the blind spot of the other.
- its located outside of the macula (away from detail vision)
- the brain “fills in” the spot.
What breakdown in they leads most specifically to loss of central (detail) vision?
A. Presbyopia
B. Cataracts
C. Macular degeneration
D. Retinitis pigmentosa
E. Glaucoma
C. Loss of Central Vision
Rod spectral sensitivity
Most responsive at ~500 nm.
Cone spectral sensitivity
Most responsive at ~560 nm.
L- cones
Most numerous
S-cones
Fewest in number
Least Responsive
Modularity
The idea that specific areas (modules) of the brain are specialized to process certain types of information or perform certain functions.
Sensory modularity
Suggest that specific brain regions are responsible for processing certain types of sensory information.
- The sensory info should be initially processed independently from other senses. (No mixing)
Primary Receiving Areas
Occipital Lobe, Temporal Lobe, Parietal Lobe, Piriform Cortex, Insula and Operculum.
Occipital Lobe
Vision
Temporal Lobe
Audition
Parietal Lobe
Touch
Piriform cortex
Smell
Insula and Operculum
Taste
Neuron
The basic unit for processing information.
Composed of: cell body (soma), dendrites, axon.
Neurons can be triggered by:
- chemical signals (neurotransmitters)
- electrical signals (action potentials and gap junctions)
- environmental signals
Action Potential
Main ways neurons transmit info to each other.
When it happens, there are voltage change.
It can fire spontaneously and sporadically without stimulation.
Remains the same size.
Increasing signal intensity can increase rate of firing.
If the neuron passes the threshold of excitation, you get an action potential
Action potential path
Starts in the Axon hillock, travels to axon terminal, and neurotransmitters will release, causing action potential in the next neuron.
When neurotransmitters sent from another neuron binds to a receptor, ion channels can open ____, _____.
ESPS & ISPS
Both are graded potential
ESPS Excitatory Postsynaptic Potential
An influx of positively charged ions (na+) pushes the neuron toward depolarization
- increase the likelihood of firing
IPSP Inhibitory Postsynaptic Potential
An effluent of positively charged ions (k+) makes the neuron more polarized (hyper polarized)
- decrease the likelihood of firing
In a typical neuron, what kind of signal would drive the resting potential towards the threshold of a citation, and potentially pass it in order to produce an action potential?
EPSP
When neurons fire together as a result of stimulation, they form a ___.
Neural circuit
Simple neural circuit
Isolated pairs excitatory neurons and a target neuron.
Complex neural circuit
Formed through the convergence of synapses onto a single cell.
Vertical circuit
Rods and cones send signals vertically through bipolar cells and ganglion cells.
Horizontal circuit
- Signal sent horizontally between receptors by horizontal cells.
- Signal sent horizontally between bipolar and ganglion cells by amacrine cells.
How do retinal cells converge?
- 126 million rods and cones converge into 1 million ganglion cells.
- Higher convergence of rods than cones:
120 rods: 1,000,000 ganglion cell. 6 cones: 1,000,000 ganglion cell. - Many cones in the fovea has one to one relationship to the ganglion cell.
True or false: there are more rods and cones in the retina
True
Why don’t we noticed we have a Blindspot in our vision? Check all that apply.
The Blindspot is in different areas of the field of view of each eye.
Our brains fill in any gaps in our field of vision .
It is located outside of the macula away from the detail vision .
All are true
The Purkinje shift occurs when moving from light to dark and refers to ___ system sensitivity to shorter wavelength of light during dark adaptation.
Enhanced or decreased
Enhanced
Rods or cones: Which photo of receptor has a higher convergence rate?
Rods
When excitation is stronger, you get _____ action potential. When inhibition is stronger, you get ___ action potentials to the point of ____
More; fewer; going below the spontaneous resting rate.
