The eye

• Structure and function


  How the eye responds to light
• Stimulus and Response


  1. Receptor

  2. Effector

  3. Sensory neurone

  4. Relay neurone (in CNS)

  5. Motor neurone
• The eye


  • Iris
  • Pupil
  • Sclera
  • Cornea
  • Lens
  • Optic nerve
  • Retina
  • Ciliary muscles
  • Suspensory ligaments

  
• Responding to light


  1. Light rays reflect into the eye and are refracted by the cornea and lens onto the retina

  2. Light receptors on the retina detect an increase/decrease in light intensity

  3. Electrical impulse is sent along the sensory neurone to the CNS and back via the motor neurone

  4. Circular muscles in the iris contract/relax and the radial muscles in the iris relax/contract

  5. The pupil constricts/dilates

  
• Light intensity


  • Pupil size
  • Circular muscle
  • Radial muscle

  
• The size of a pupil is changed by a reflex action
• Blink reflex


  1. Light rays reflect off of the object and into the eye

  2. The cornea and lens refract the light rays onto the retina

  3. The light receptors on the retina detect the light and generate an electrical impulse that is sent along the sensory neurone to the spinal cord

  4. The electrical impulse travels along the motor neurone to the muscles in the eyelid which contract
• Eye changes in bright light

  1. Light rays reflect off of the object and into the eye

  2. The cornea and lens refract the light rays onto the retina

  3. The light receptors on the retina detect the light and generate an electrical impulse that is sent along the sensory neurone to the relay neurone

  4. The electrical impulse travels along the motor neurone to the circular muscles in the iris which contract

  5. The pupil becomes constricted

  
• Image formation on the retina and transmission to the brain

  1. Light rays are reflected off of the object and enter the eye through the cornea and pupil

  2. The light rays are refracted by the cornea and lens so that they focus on the retina

  3. Light falling on the retina stimulates light receptors and an electrical impulse is generated which travels along the sensory neurone (optic nerve) to the brain