Sensory system: The eye & the central visual system
정성권 (schung@med.skku.ac.kr)
http://www.physpharm.fmd.uwo.ca/undergrad/sensesweb/index.htm
Structure of eye
1. Focusing carried by cornea, lens, and pupil
2. Organization of retina: functional roles of 5 different neuron types in the retina
Signal transduction in photoreceptors
1. dark current
2. Photoisomerization of rhodopsin - http://www.blackwellpublishing.com/matthews/rhodopsin.html
* signal amplification
3. Receptive field in retina: “on” and “off” center ganglion neurons
* Lateral inhibition - http://cas.bellarmine.edu/tietjen/Animal%20Behavior/lateral_inhibition.htm
** What is the advantage to have antagonist surround?
4. M-, P-, nonM-nonP-type ganglion cells: very color sensitive
Color vision
1. Color-opponent cells: color adaptation
2. Double-opponent cells: color sensitivity, explains color adaptation
Targets of optic track
1. LGN → optic radiation → primary visual cortex
2. Transection in the optic track and the visual defects
3. Non-thalamic targets of the optic track
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hypothalamus: biological rhythm (sleep/ wakefulness)
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pretectum: control the size of pupil
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superior colliculus: saccadic eye movements, quick jump in eye position
4. Input, output in LGN
Primary visual cortex
1. Retinotopy: brain’s interpretation of distributed patterns of activity
2. Six cell layers in cortex: ocular dominance columns
Layer IVC → layer IVB, III (binocular input)
Patterns of outputs
Assignments
Q1. What are the reasons for the following eye disorders?
Cataract
Glaucoma
Q2. What is the major reason for the presbyopia (old eye)? And how would you fix the problem?
Q3. What is the function of pigmented epithelium in visual system?
Q4. Illumination on photoreceptor induces hyperpolarization. Why?
Q5. There are two reasons why the rod system has poor visual acuity. Explain them.
Q6. The response of a bipolar cell’s membrane potential to light in the receptive field center is opposite to
that of light in the surround. Explain the mechanism for this arrangement.
Q7. How does the brain compute what it must using so few active neurons?
Q8. Early visual scientist thought that a large bright light would best activate ganglion cells. Why were they
wrong?
Q9. Draw the stimulus that would maximally activate an off center ganglion cell.
Q10. The prolonged exposure to red light produces a shade of green in white back ground. Why?
Q11. What are the functions of some retinal ganglion cell’s projections to hypothalamus and pretectum?
Q12. What are the dimension and the function of “cortical module (hypercolumn)”?