Summary of Photoreceptors (rods vs cones) | Processing the Environment | MCAT | Khan Academy

Main Ideas and Concepts:

Definition of Photoreceptors:
- Photoreceptors are specialized nerve cells that convert light into neural impulses.
- Rods and Cones are the two types of Photoreceptors in the retina.
Structure:
- Rods:
  - Elongated, rod-shaped cells.
  - Contain optic discs with proteins (Rhodopsin) that absorb light and trigger a phototransduction cascade leading to action potentials.
- Cones:
  - Cone-shaped cells.
  - Also contain optic discs with proteins (Photopsin) that function similarly to Rhodopsin in Rods.
Quantitative Differences:
- Approximately 120 million Rods versus 6 million Cones in an average retina (20 times more Rods).
Location in the Eye:
- Rods are primarily located in the periphery of the retina.
- Cones are concentrated in the fovea, the central region of the retina.
Functionality:
- Rods:
  - Responsible for black and white vision.
  - Highly sensitive to light (1,000 times more than Cones), making them effective for low-light conditions.
- Cones:
  - Responsible for color vision.
  - Less sensitive to light but essential for detecting colors (red, green, and blue Cones).
Recovery Time:
- Rods have a slow recovery time, meaning they take longer to reset after being activated by light.
- Cones have a fast recovery time, allowing for quick adaptation to changes in light conditions.

Understanding Phototransduction:
- Light hits the photoreceptor (rod or cone).
- The protein (Rhodopsin in Rods, Photopsin in Cones) absorbs the light.
- This triggers a cascade of biochemical reactions leading to the firing of an action potential that is sent to the brain.
Adaptation to Light Changes:
- Rods: Gradual adjustment to dark conditions (e.g., entering a dark room).
- Cones: Rapid adaptation to bright conditions (e.g., transitioning from outside to indoors).

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