Physiology 3120 Lecture Notes - Lecture 6: Color Vision, Prosopagnosia, Feature Extraction
9 May 2018
School
Department
Course
Professor
Physilogy 3120
Dr. pruszynski
Lecture 6
Visual System
Peripheral Visual System
- Light comes in through pupil and terminates on retina (back of eye)
- Light has to pass through these neural tissues to hit back of eye, where it is transduced by
photoreceptors
- Within retina, there is various classes of neurons:
o photoreceptors
▪ actual transduction elements
▪ turn photons into release of neurotransmitters
▪ no spiking activity – just graded potential
o Bipolar cells
▪ connect to ganglion cells
▪ No spiking activity – just graded potential
o Ganglion cell
▪ Output of retina
▪ Spiking activity
▪ when we talk about receptive fields, we are talking about the receptive fields of
the ganglion cells
Receptors
- Rods (night vision)
o Concentrated in peripheral retina (mostly in outside of field of view)
▪ That’s why its hard to read something in your peripheral vision
o Sensitive faint light (more pigment, convergence, 100:1)
o Have more pigment (more capacity of transforming photons into graded potentials)
o Highly convergent (there are many rods converging at the output level)
o When you have more convergence, you lose acuity
- Cones (day vision)
o Concentrated in fovea - thumb nail at arm’s length
o Greater acuity/sharper image (less convergence, 6:1)
o Bright light
o Color vision
find more resources at oneclass.com
find more resources at oneclass.com
Fovea
- 0 means the part that you are looking at – the part that you are
foveating
- if you hold your hand out and look at your thumb, the info of the
fingernail is landing on the fovea (where there is an
overrepresentation of the cones)
- y axis is the density (number of receptors per sq mm)
- at the fovea, you have a lot of cones
- in peripheral vision, you have lots of rods
Transduction of Light
- in the dark, the photoreceptors have open Na+ channels depolarized
- when light hits the pigment element (rhodopsin), the Na+ channels close hyperpolarization
Action Potentials in the dark
- in the dark, the photoreceptor is depolarized and is releasing neurotransmitter r(glutamate)
- in the light, the photoreceptor becomes hyperpolarized and stops releasing neurotransmitter
r(glutamate)
- this communication gets to the next cell in the chain, the bipolar cell
find more resources at oneclass.com
find more resources at oneclass.com
