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1. Which type of photoreceptors retect low light levels?
2. Color, acuity?
- 1. Rhodopsin
- 2. Peripheral to fovea
- 3. Highly convergent
- 1. 3 Cone opsins
- 2. Fovea
- 3. Less convergent
What are the receptors activated in the following levels of illumination?
- 1. Cones
- 2. Rods and Cones
- 3. Rods
How do photoreceptors respond to light?
- Change in photopigment molecule
- Hydrolysis of cGMP --> closes cGMP-gated Na channels
- Membrance hyperpolerizes from 30 mV
- Decreases amount of inhibitory neurotransmitter released to bipolar cell
What are the targets of the ganglion cell axons?
- Lateral geniculate body
- Superior colliculus
- Pretectal Olivary Nucleus
What cell types modulate photoreceptor interactions with bipolar cells?
What is the pathway and function of the off-surround response?
- Pathway: photoreceptors hyperpolarize adjacent horizontal cells, which depolarize the on-center receptor (bipolar cell hyperpolarizes)
- Responsible for sharpening boundaries between light and dark
If both on-center and off-surround photoreceptors are stimulated, what will be the resulting ganglion cell firing rate?
No change from basal firing rate
What wavelengths are the following cones most sensitive to:
- 1. 419 nm
- 2. 531 nm
- 3. 559 nm
Which type of cones are most sensitive to light? Least sensitive to light?
- Most sensitive - red cones
- Least sensitive - blue cones
1. Which cones are found in the central region of the fovea?
2. Why is one left out?
- 1. Red and green cones
- 2. Blue cones are left out because of chromatic aberration (blue refracts through lens at too great an angle, so image would be blurry)
When a single type of cone is missing or non-functional, what is the result?
- Red-green color blindness
- X-linked recessive