coordination and response part 2

• A stimulus is any change in the environment that can be detected by structures called receptors
• Sense organs and the stimuli they respond to

  • Skin - touch and temperature
  • Tongue - chemicals in food and drink
  • Nose - chemicals in the air
  • Ear - sound
  • Eye - light
• Eye structures

  • Cornea
  • Iris
  • Pupil
  • Lens
  • Retina
  • Fovea
  • Optic nerve
  • Blind spot
  • Suspensary ligaments
  • Ciliary muscles
• Cornea

  Refracts or bends light when it enters the eye
• Iris


  Controls how much light enters the pupil
• Lens

  Focuses light onto the retina
• Retina

  Contains light receptors some sensitive to different colors
• Optic nerve


  Carries impulses to the brain
• Pupil reflex

  1. Pupil diameter gets smaller/constricts in bright light

  2. Pupil diameter gets larger/dilates in dim light
• Antagonistic muscles in the iris

  Circular muscles and radial muscles
• Accommodation

  1. Ciliary muscles contract, suspensory ligaments relax, lens thickens for near objects

  2. Ciliary muscles relax, suspensory ligaments stretch, lens thins for distant objects
• Retinal receptors

  • Rods - used for night vision
  • Cones - used for color vision
• Rods are found all over the retina except at the blind spot and fovea, cones are concentrated at the fovea
• The blind spot is the area where the optic nerve leaves the eye and has no photoreceptor cells
• Fovea

  Small part of the retina with high concentration of tightly packed cone cells for sharp, color vision