Lecture 8

-EYE

• Detects electromagnetic waves from wavelength of 400-750nm (visible light)
  
• Detects EM waves using rods and cones
  
  • Rods  function in dim light, they're very sensitive, can respond to a single photon of light, doesn't see colors (black and white are colors), all you see is shades of grey with a rod
    
  • Cones  function in bright light, record color images
    
    • White = all colors at once
      
    • Black = none of the colors
      

• a rod has free floating discs in outer segment
  
  • each of these discs has a photopigment in the outer surface of its membrane, this pigmented membrane is going to pinch off the end of the rod and consume discs and and three new discs are made every hour, discs are made at the bottom and migrate upward
    
• photopigment called rhodopsin (is 11 cis-retinale + scotopsin)
  
  • 11 cis-reinale goes through a series of shape changes
    
    • One is the
      

    This opsin is called scotopsin in rods (the opsin of rhodopsin)
    

    -when only looking with rods (not enough light stimulating cones) using scotopic vision
    

  -if we turn up the light to bright light, the rod gets flooded with too much light and can't function and you are only using cones, this is called photopic vision
  

  -when use both rods/cones  mesopic
  

  -which one, rods/cones, is based upon how much light is available
  

  -rod has peak absorption of 505 nm
  

  -in dark the rod fires, ion channels open and Na and Ca flood in
  

  -the ion channels are held open by cyclic GMP and Na/Ca come in
  

  -think of Na as the main thing that causes the release of the NT
  

  -Ca plays a special role in NT release
  

  Cyclic GMP formed by glymulate cyclase, but is inactivated by Ca entering the cell, this causes cyclic GMP to be reduced and the amount of Ca coming in is reduced, when Ca is reduced more cyclic GMP is made
  

  THIS IS A CYCLE, it does not open or close it just finds a happy medium
  

  -when get rid of the light, hitting the rod, this process changes
  

   
   

  ______________________________________________________________________________________________________________
  

  http://en.wikipedia.org/wiki/Photoreceptor_cell
  

   
   

  ONE photon works for rods, not for cones
  

  • CAN change one rodopsin molecule, making one metarhodopsin
    
  • One meta can change 100s of transductions
    
  • One transduction can stimulate 1000s of
    

     
     

  Scotopic vision
  

  • No color, only the rods were working
    

   
   

  Photopic vision
  

  • In normal light, rods are maxed out and not really functioning
    

   
   

  Mesoptic vision
  

  • Transition period between the 2
    

   
   

  Types of cones:
  

  • Long wave cone
    
    • Peaks at 557 nm
      
    • Only one to see red
      
    • In yellow spectrum
      
    • longwaveconeopsin
      
  • Medium wave cone
    
    • Peak at 535 nm
      
    • mediumwaveconeopsin
      
  • Short wave cone
    
    • Peak at 420 nm
      
    • Shortwaveconeopsin
      

       
       

  660 nm - bright red (paper)
  

  410 nm - bright violet - (disk on it)
  

  TINY dot is a hole in disk
  

  Put you in dark room, with strobe light
  

  If we can get DOT in center of foveola, since there are no short wave cones…it disappears!
  

  Analysis AT BRAIN, not receptors - it sees what it wants
  

   
   

  Daishi
  

  € Invar
  

  it
  

  
   

  or
  

   
   

   
   

   
   

   
   

   
   

   
   

   
   

  Light hits Cone A center
  

  hyperpolarizes
  

  Glutamate coming out of A slows down
  

  A bipolar cell Na channels held down by glutamate
  

  Therefore more Na channels open and increase output of A
  

  Therefore ON CENTER
  

   
   

  B hit by light
  

  B bipolar cell Na channels held open by glutamate
  

  Therefore reduction in glutamate closes channels, output is decreased
  

  THEREFORE OFF CENTER
  

   
   

  Center surround antagonism
  

   
   

  ROD bipolar cells are only ON Center
  

   
   

  http://en.wikipedia.org/wiki/Bipolar_cell_of_the_retina
  

   
   

  Ganglion cells
  

   
   

  W - 40%
  

  • Connect mainly via amacrine cells?
    
  • Directional movement
    
  • Important in scotopic vision
    

   
   

  X - parvo cells - 55%
  

  • Color
    
  • Shape
    
  • Firing tonally
    
  • Main transmitter of visual image
    

   
   

  Y - magno cells 5%
  

  • Rapid changes in visual field
    
  • Movement
    
  • Intensity
    
  • Phasic bursts
    

     
     

   
   

  Uri is
  

   
   

  http://en.wikipedia.org/wiki/Visual_system
  

   
   

  Layers of LGN
  

   
   

  End in layer 4
  

   
   

  LGN and cortex have visual maps
  

  • Foveola has largest mapping
    

     
     

  Cortex
  

  • Blobs
    
  • No blobs - layers 2 and 3 - interblob areas
    

     
     

     
     

Parvo blob	Color
Parvo - interblob	Shape
Magno - movement	Depth of field, location

 
 

 
 

 
 

EAR

 
 

• Inner ear has sensors to detect rotational acceleration
  
  • Semicircular canals
    
• Head position and linear acceleration
  
  • Utricle and saccule
    
• Choclea
  
  • Sound
    

Semicircular canals have endolymph

•  
  

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

5

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