Structure of the Eye and Iris Reflex

Eye Anatomy

• Cornea
  • Transparent, no blood vessels.
  • Oxygen diffuses from the air.
  • Refracts/bends light.
• Iris
  • Colored part of the eye.
  • Controls pupil size.
• Pupil
  • Not a structure, but a gap in the iris.
  • Allows light to pass to the lens.
• Lens
  • Refracts light.
  • Can change shape to focus light on the retina.
• Retina
  • Contains receptor cells: cone and rod cells.
  • Cone cells: sensitive to color, not effective in low light.
  • Rod cells: sensitive to light, see in black and white.
• Fovea
  • Concentrated with cone cells.
  • Focus area for clear vision.
• Optic Nerve
  • Transmits impulses from receptor cells to the brain.

Iris Reflex

• Purpose: Protects retina from light damage.
• Bright Light
  • Pupil constricts (small size).
  • Circular muscles contract, radial muscles relax.
• Low Light
  • Pupil dilates (large size).
  • Circular muscles relax, radial muscles contract.
• Muscle Types
  • Circular Muscles: Around the pupil.
  • Radial Muscles: Stretch from inside to outside, like a radius.

Conclusion

• Bright light causes constriction to protect the retina.
• Low light necessitates dilation for better vision.
• Understanding muscle function is key to understanding pupil size changes.

These notes summarize the key points from the lecture on the eye's structure and response to light intensity changes via the iris reflex.