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Homeostasis, the Eye and the Brain (Nervous System (Central Nervous System…

- - - - Synapses- connect neurones by impulses in the form of chemical neurotransmitters which set off an elec. impulse in the next neurone
  - - - Sensory neurones carry impulses from receptor to CNS
      - Motor neurones carry impulses from coordination centre to effector, providing a response which requires no conscious thought
- - - - In BRIGHT light, the iris' circular muscle contracts and the radiat muscles contract to allow less light into the eye
      - In DIM light, the radial muscles contract and the circular muscle relaxes, widening the pupil and allowing more light to enter the eye
    - - To look at NEAR objects, the ciliary muscles surrounding the lens contract and the suspensory ligaments relax, thickening the lens, allowing more refraction and greater detail of the picture.
      - To look at FAR objects, the ciliary muscles surrounding the lens relax and the suspensory ligaments contract, thinning the lens, allowing less refraction.
  - - - Lens does not refract enough or eyeball is too short- image is focused BEHIND the retina
        
        Solution = convex () lens glasses which refract light to focus on retina
    - - Lens refracts too much or eyeball is too long, image is focused IN FRONT of the retina
        
        Solution = concave )( lens glasses which refract light outwards so that the lens refracts it less and it will focus on retina .
    - - Convex/concave glasses
      - Contact lenses (PROS: Lightweight, hard to see, useful for sportspeople, CONS: Risk of eye infection)
      - Laser eye surgery to change cornea shape (PROS: Precise and effective CONS: Risk of infection/complication)
      - Replacement lenses (PROS: Effective for longsightedness CONS: Higher risk of infection and retina damage which will hinder sight)