Sense organs

• Sense organ


  Groups of receptor cells that respond to specific stimuli or changes in the environment such as light, sound, touch, temperature and chemicals
• Eye


  • Protects the internal structures
  • Refracts or bends light to help focus it
• Cornea


  Tough transparent curved layer located at the front of the eye
• Iris


  Colored ring of muscles that controls the size of the pupil
• Pupil


  Circular opening at the center of the iris that lets light into the eye
• Lens


  Clear flexible structure that refracts light to focus it onto the retina
• Retina


  Lining on the inside surface at the back of the eye that contains millions of light sensitive receptor cells
• Blind spot


  Small area on the retina directly in front of the optic nerve that contains no light sensitive cells
• Pupil reflex


  1. Pupil constricts in bright light

  2. Pupil dilates in dim light
• Pupil reflex


  • Muscles of the iris respond by constricting or dilating the pupil
  • Unconscious process
• Circular muscles


  Muscles in the iris that constrict the pupil
• Radial muscles


  Muscles in the iris that dilate the pupil
• Accommodation


  1. Lens changes shape to focus on near or distant objects

  2. Ciliary muscle contracts or relaxes to change lens shape
• Rods


  Light sensitive cells in the retina that are sensitive to low light intensities and enable night vision
• Cones


  Light sensitive cells in the retina that enable color vision in bright light
• Fovea


  Small depression at the center of the retina responsible for central vision and high visual acuity
• Peripheral vision is less defined than central vision focused on the fovea