Please enable JavaScript.

Coggle requires JavaScript to display documents.

:eyes: (Photoreceptor cells (Organisation (Rods (Dim light) (Rhodopsin…

- - - - Store chemical substituents which respond to light
  - - - Rhodopsin photopigment
    - - Three photopigments (Blue, green, red)
    - - Contain opsins
        
        Membrane-bound proteins
        
        Bound to a chromophore molecule
        
        Retinal
        
        Vitamin A derivative
        
        Light sensitive
    - - Absorbed all bypassed light
  - - - Retinal undergoes conformational change
        
        Activates transducin
        
        Activates phosphodiesterase
        
        Deactivates guanylyl cyclase
        
        Cation channels close and cell hyperpolarises
    - - Guanylyl cyclase is ACTIVE
        
        cGMP concentration is high
        
        Ligand gated cation channels are open
        
        Na and CA influx keep depolarised state
- - - - White sclera
        
        Gives shape to eye
        
        Protects inner part
        
        Increases rigidity
        
        Allows extension of muscles to control eyeball movement within sockets
      - Cornea (front part)
    - - choroid
        
        Absorbs light at the back of the eye
        
        Dark melanin pigment forming the back of the eye
      - iris
        
        zonular fibres and ciliary muscles
        
        control shape of lens
        
        Circular and radial smooth muscles control size of pupil
        
        Allow light into eye
    - - back of the eye
      - Contains photoreceptors
      - Fovea centralis
        
        Part of the eye most sensitive to light
        
        Site of image focusing
  - - - Between lens and cornea
        
        Clear fluid
        
        Supply oxygen and glucose to relevant portion
    - - Between retina and lens
        
        Viscous, jellylike
        
        Gives shape to eye
- - - - Ciliary fibres contract
        
        Tension on zonular fibres decrease
        
        Lens becomes spherical/concave
    - - Ciliary muscle relaxes
        
        Diameter of muscle ring increases
        
        increased tension on zonular fibres
        
        Lens becomes concave/flattened
    - - Presbyopia
        
        Eyeball too short/lack of elasticity in the ciliary muscles
        
        Image focused behind retina
        
        Unable to accomodate far objects
- - - - Interact via two pathways
        
        ON pathway
        
        OFF pathway
        
        Difference is the type of glutamate receptor activated in bipolar cells
        
        complete opposite response in presence and absence of light
    - - Axons direct output from retina meeting at the base of the optic chiasm
        
        Terminate in the lateral geniculate nucleus in thalamus
        
        LGN transmits action potential to visual cortex for interpretation
        
        Other terminals
        
        Suprachiasmatic nucleus
        
        superior to optic chiasm
        
        Controls biological clock
        
        Brainstem and cerebellum
        
        hand-eye coordination
      - Some fibres crossover and travel to optic tracts of opposite sides of brain
        
        Provide cerebral hemispheres with input from each eye
    - - Horizontal cells
        
        Transmit inhibitory signals to adjacent neurons of activated rods and cones, enhance contrast
      - Amacrine cells
        
        Transmit changes in terms of illumination levels to ganglion cells, determining brightness