Visual Process Flashcards
Explain wavelengths. (What they are ? Electromagnetic Spectrum and their dimensions)
-> Wavelengths refers to the distance between the two apexes of a wavelengths.
-> Wavelengths are also called frequencies.
-> Three dimensions are (Hue, Brightness and Saturation)
List out the structure of the eye (also the two properties of images on the retina).
-> Cornea: The outmost part of the eye. Helps us focus.
-> Extraocular muscles: Help human move our eyes, as we don’t have universal vision.
-> Iris: The coloured part of the eye. These are formed by tiny muscles that are used to control the size of the pupil.
-> Pupil: Controls the amount of light that enter the eye.
-> Lens: Further focuses on the light onto the retina.
-> Retina (2 properties): Where the cells and photoreceptors are. Objects are inverted on the retina. Also, lights from the above are focused on the lower retina, whilst lights from the below are focused on the upper retina.
Properties of the Retina and the Fovea.
-> The center of the retina is the fovea.
-> Fovea provides refined imagery while peripheral areas do not.
-> The further away from the fovea, the fewer photoreceptors there are.
-> There are more cones than rods in the fovea, vice versa in the peripheral.
-> When there is more light, cones will be more responsive. When there is darkness, the rods take over.
Explain the three cells (and 2 connecting cells) in the Retina and their ratio distribution.
-> 1st layer: Retinal Ganglion Cells (RGCs): The only cell in the retina that releases action potentials. The axons of the RGCs form the optic nerve.
-> 2nd layer: Bipolar cells: The bipolar cells are in the middle between the RGCs and the photoreceptors. They release receptor potentials when they are depolarised.
-> 3rd layer: Photoreceptors: Cones and rods. Resting membrane potential is less polarised as the ion channels are mostly opened. The photopigments in the photoreceptors are the reason why they are responsive to light.
-> Horizontal and the Amacrine cells are in between the photoreceptors and the bipolar cells, and between the bipolar cells and the RGCs respectively.
> When the photoreceptors receive light, photopigments are splitted, which shut the ion channels. The calcium + and sodium + gates are closed means there will be less receptor potentials released and the hyperpolarisation of the photoreceptors. Then glutamate is not released, and excites the bipolar cells
-> The ratio of photoreceptors to bipolar cells to RGC is 1:1:1 at the fovea. However, in the periphery area, the ratio can be x:y:1.
Explain the Transduction of Light into Electrical Signals in the Retina.
-> Firstly, when light enters the photoreceptors, photopigments inside are split into two.
-> When the photopigments are split into two, there are receptor potentials released, which close the the ion channels on the photoreceptors.
-> The ion channels on the photoreceptors are normally opened, which allows the influx of + ions (NA+ and CA+). This is why the photoreceptors are less polarised. However, with the channels shut, the membrane potential is hyperpolarised, which does not releases glutamate.
-> With glutamates are not released, it triggers the bipolar cells to depolarise, which also releases receptor potential and triggers action potential of the RGCs.
The Pathway of Visual Information
Objects from the right visual field:
-> The object enters the temporal retina in the left eye, and the nasal retina in the right eye.
-> The objects travel to the optic chiasm (where the information of both eyes meet).
-> It continues to travel to the left lateral geniculate nucleus.
-> Goes to the left primary visual cortex (route being named as optic radiation)
- The three cone types with different spectral sensitivities
- What is the name of normal colour vision?
- Name of colour blindnesses
- Test to examine colour blindness
-> Blue (419 Hz) -> Rod (496 Hz) -> Green (531 Hz) -> Red (559) Hz
-> Trichromatic Vision: The ability to view all three colours.
-> Lacking of Green cones: Deuteranopia; Lacking of Red cones: Protanopia
-> The Ishihara Colour Plates Test is used to test colour blindness
Explain On-Off Cells.
On cells: Center of the receptive field: inhibiting the RGCs if there is light; Peripheral of the receptive field: exhibiting the RGCs if there is light.
Off cells: Center of the receptive field: exhibiting the RGCs if there is light; Peripheral of the receptive field: inhibiting the RGCs if there is light.
The pattern of the light falling on the receptive field affects the on-off balance of the RGCs.
What is the Retinohypothalamic Pathway:
The Retinohypothalamic pathway is a pathway which facilitates the regulation of the body clock. It happens at the suprachiasmatic nucleus. The cell that is mainly responsible for the regulation is the melanopsin.
Bionic eye:
-> For people who have damaged photoreceptors.
-> Requires a right pattern of stimulus of the RGCs.
-> Only see light dots to know roughly what they are looking at.
Explain the Retinogeniculate Pathway
the pathway of the information of LGN to the primary visual cortex
3 layers of neurons of the pathway
1-2: magnocellular layer: the inner layers. Mostly responsible for movements
3-6: parvocellular layer: the outer layers. Mostly responsible for colour perceptions
In the middle of the each layer: Koniocellular layers: mixture of both
Information also spotted to travel back to the geniculate nucleus. Unexplainable
