Senses and Communication - Summary

Senses & Communication

Light

  • Light is an electromagnetic wave or stream of photons.
  • Visible light ranges from 300-800 nm.
  • Luminance/Radiance: Light emitted from an object (unit: lumen, ~4 x 10^9 photons).
  • Illuminance/Irradiance: Light falling on a surface (unit: Lumens per square meter).
  • Short wavelengths damage tissues while long wavelengths pass through.

Light Transmission & Attenuation

  • Sunlight is broad spectrum and attenuates as it travels.
  • Absorption, reflection, and transmission vary by wavelength.
  • Color and brightness depend on the environment and pigments.

Bioluminescence

  • Light produced by living organisms; less intense than sunlight.
  • Involves Luciferin and Luciferase chemical reaction.

Eye Evolution

  • Flat light-sensitive arrays can evolve into focused lens eyes in a few hundred thousand years.

Vision

  • Requires reflection, straight-line transmission, and refraction.
  • Refraction focuses light using a lens.
  • Diffraction bends waves around objects.

Vertebrate Eye Structure

  • Sensitivity: Performance in low light.
  • Resolution: Ability to distinguish detail.
  • Refraction/focusing by cornea and lens.
  • Fovea: High visual acuity area.

Photoreceptor Cells

  • Rods: Contrast detection in low light (spatial summation).
  • Cones: Color detection in bright light (usually 1 cone - 1 neuron).

Photoreceptor Types

  • Two classes: microvillar and ciliary.
  • Invertebrates: microvillar.
  • Vertebrates: ciliary.

Cephalopod Eyes

  • Lack rods and cones; use microvillar photoreceptors.
  • Different pigments than vertebrates.
  • Retinal design more direct (“sensible”).

Compound Eyes

  • Ommatidia receive light from a narrow angle.
  • Lightweight solution for small, mobile organisms.

Apposition & Superposition Eyes

  • Apposition: Ommatidia sheathed by pigment cells.
  • Superposition: Light leaks between ommatidia.

Color Vision

  • Achieved by different photoreceptors absorbing different wavelengths.
  • Receptors with overlapping sensitivities.
  • Colored oil droplets act as filters.
  • Dichromat: two cone types.
  • Trichromat: three cone types.
  • Tetrachromat: four cone types.

Nocturnal Species

  • Large eye and pupil size.
  • Large lens and short focusing distance.

Sensitivity & Resolution

  • Better resolution: larger eyes, tighter photoreceptor packing, high cone:rod ratio.
  • Better sensitivity: larger eyes and pupils, high rod:cone ratio, tapetum.