the eyes

Question 1

The electromagnetic spectrum:

Answer 1

• Ability to distinguish different levels of the electromagnetic system which is between 400-700 nanometers
• Color is what our brain processes the signal as.

Question 2

the human eye

Answer 2

• Extraocular muscles: used to position eyes In different locations, so our retina can process the information with high validity
  Cornea, lens, light processes through here and make sure image is focused.

Question 3

the retina and fovea

Answer 3

• Fovea= part of retina where we have the highest density of photoreceptors, that’s why we move our eyes so the reflected light hits the Fovea.
  
  • Cone types help us see color, there is three different cone types
    At higher light levels we have three cone types that are active, at low light levels we have one rod active, which is why we cant see color in the dark.

Question 4

cells of the retina (this is a big one)

Answer 4

• Visual stimulus means light falls on the retina
  
  • Where the photo receptor is, we can see there is a change in the membrane potential and that means the voltage difference between the inside and the outside of the cell is changing in response to this ligjt
  • Its not an action potential at the first state, but the fluctuation in the membrane potential then causes changes in the bipolar cell, goes in different polarity but then induces a change in the ganglin cell, which does produce action potentials.
    So based on the electrical changes in the photoreceptors and the bipolar cells, we will then get changes in the ganglin cells, possibly action potentials in response to this light that will then go to the brain.

Question 5

three cone types

Answer 5

blue cone= has the most response at wavelength 419, if it was 400 the response would be lower

Question 6

cone combination in the fovea and periphery

Answer 6

A change in the light position will result in a big change in activity within the ganglia cells.
- This explains why we have less spatial resolution in our periphery and much better when the eye is focused on a specific point

Question 7

interactions in the retina

Answer 7

• Each ganglion cell responds to light stimulation of a small region on the retina. Diagram on the left is an image of individual photo receptors within the retina, red circles represent the photoreceptors which trigger responses to the ganglion cell.

Question 8

visual pathways in the brain

Answer 8

• crossection between the right hemisphere (RH), 80-90% of signals come back to the PVC.
• light from the left visual field goes to both eyes, however the retinal ganglion cells from the nasal retimal left eye end up crossing over the optic eyes and coming back to the right thalamus
• we can also see the corresponding fribres for the left visual field in the right eye and the temporal retina on the same sight coming back to the right hand side.

Question 9

the retinogeniculate pathway

Answer 9

• retina —> LGN
  the lateral geniculate nucleus (LGN) contains six layers of neurons.
• the inner two are magnocelluar (M) layers
• the outer four are parvocelluar (P) layers
• the koniocelluar (K) sublayers are found below each of the M and P layers
  = prjects to the PVC and associated w conscious perception

Question 10

Centre surround receptive field structure in the LGN

Answer 10

• receptive fields of LGN neurons have a centre-surround organisation.
• each LGN neuron responds to light stimulation of a small location in the real world
• retinotopic: we can record action potentials from neurons in the LGN

Question 11

retina hypothalamic pathway:

Answer 11

• the suprachiasmatic nucleus (SCN) recieves light information from the environment,
• entrains behaiour to a 24-hour light/dark cycle
• when we wake, eat
• the retina to hypothalamus which provides light to circadium pathways
  melanopsin cells help synchronize our lives

Question 12

the bionic eye

Answer 12

• the device consists of a camera for collecting visual scene information
• a receiver for processing the image data
• an implant that coverts the image data to electrical impulses in the microelectrode array.
• useful for blindness where photoreceptors are damages- not if the optic nerve damage

Question 13

whats it like to see with a retinal implant

Answer 13

• the implant generates an array of phosphenes
• the array of photophones like a picture made up of light dots
• good for locating hazards

Question 14

visual pathways

Answer 14

• conscious vision involves neurons in the LGN
• our biological clock is synchronized by the melanopsin ganglion cells

Question 15

transduction of light into the neural signals

Answer 15

• structure and function of retina
• photoreceptors and ganglion cells
• receptive fields