Chapter 14: Coordination and Response: II Animal Receptor Organs

The Mammalian Eye

• %%Cornea%%
  • A clear layer coating iris.
  • Refracts light in the eye.
• %%Iris%%
  • Colored section of eye.
  • Controls amount of light entering by contracting and dilating pupil.
• %%Pupil%%
  • Allows entrance of light.
• %%Lens%%
  • Behind iris.
  • Focuses image on retina.
• %%Retina%%
  • Contain photoreceptors; rods and cons.
• %%Optic Nerve%%
  • Each photoreceptor cell is attached to neuron.
  • Carries nerve impulses to brain.
• %%Fovea%%
  • Section in middle of retina.
  • Provides clear images.
• %%Ciliary Muscles%%
  • Alters the thickness of muscles.
• %%Choroid Coat%%
  • Contains number of blood capillaries which nourish eye.
  • Painted black (due to supply of blood vessels) to prevent internal reflection of light.
• %%Aqueous Humor%%
  • Watery fluid.
• %%Vitreous Humor%%
  • Transparent jelly like fluid.

NOTE: both aqueous humor and vitreous humor serve to keep eyeball form and refract light.

• Rods and Cons

  

  

Controlling the entry of light in eye

• Achieved by altering diameter of pupil.
• Size of pupil controlled by iris muscles - circular and radial muscles.
• When circular muscle contract, radial muscles relax, and pupil becomes smaller.
• When radial contract, circular muscle relax , and pupil enlarges (diltes).
• Pupil enlarges when surrounding light intensity is low, and smaller when the light intensity is high.

Vision

Focusing (Accomodation)

It is the ^^adjustment of lens^^ of the eye so that ^^clear images^^ of objects at different distances are formed on ^^retina.^^

• @@Focusing on distant object@@
  • Circular ciliary muscles relax.
  • Suspensory ligaments are pulled tight - lens become flatter and less convex.
• @@Focusing on nearer object@@
  • Circular ciliary muscles contract.
  • Suspensory ligaments are released loosely - lens becomes thicker and more convex.