Chapter 10: The Visual System Flashcards
What’s the main function of the Eye?
To focus and project light onto the Retina.
Explain how light enters and travels in the eye. (5)
1) Light enters through the Pupil - which is controlled by the Iris to monitor how much light comes into the eye.
2) Light then goes through the Lens - it changes shape to focus light on the Retina.
3) Light image is FLIPPED and INVERTED onto the Retina.
4) Fovea, part of the Retina, maintains high ACUITY vision, making the Center of our vision sharper.
5) Optic Disc is where we have out Blind Spot AND whee Retinal Ganglion Cells penetrate and then exit the eye to pass on the light signal to the brain with a neural one.
Why are we unaware of out blind spot?
Due to something called the Process of Completion; using visual info around the spot to complete the image.
Identify the 5 layers of Cells in the Retina and their function.
1) Retinal Ganglion Cells: Process visual information, transmit it to the brain via their axons.
2) Amacrine Cells: Diverse, function kind of unknown - specialized in lateral communication across the layers. Receive signals from Bipolar cells and are involved in the regulation and integration of activity in Bipolar and Retinal Ganglion cells.
3) Bipolar Cells: Main pathways from Photoreceptors to Ganglion cells, i.e. the shortest and most direct pathways between the input and output of visual signals in the retina.
4) Horizontal Cells: Edges enhancement and Sharpening visual image.
5) Photoreceptor cells (Cone and Rod): specialized neurons found in the retina that convert light into electrical signals that stimulate physiological processes
Explain Cone and Rod Photoreceptors through Duplexity Theory.
Duplexity theory claims Cones and Rods mediate different types of vision: photopic and scotopic.
Cone Receptors: Photopic
- Light vision
- High acuity
- Low sensitivity with few receptors (needs more stimulation to activate)
- Low convergence! (only singular communication between layers of cells, which makes the signal stronger and maximizes acuity)
- Fovea Area
- Cone-like structure
Rod Receptors: Scotopic
- Dark/dim vision
- Low acuity
- High convergence! (each Rod is contacted by other Rods - input from many Bipolar cells. Reduces strength of signal and lowers acuity)
- High sensitivity with many receptors (why is works in dim light)
- Periphery
- Rod-like structure
What are Opsins?
Light sensitive proteins that send light within Cones and Rods - they are responsible for our Visual Spectral Sensitivity (color).
What is the Purkinje Effect?
A difference in color contrast under different levels of illumination.
True or false; There is a lack of any photoreceptors at the Blindspot/Optic Disk.
True.
Are Rods present in every class of vertebrae?
Yes they are! Very specialized in Nocturnal animals.
Identify and describe the 2 parallel channels of the Lateral Geniculate Nucleus (LGN).
1) Parvocellular Layers
- Top 4 layers of the LGN
- Made up of small body neurons
- Responsive to color, detail and slow/still objects
- Receives most input from Cone Photoreceptors.
2) Magnocellular Layers
- Bottom 2 layers of the LGN
- Made up of large body neurons
- Responsive to movements
- Receives most input from Rod Photoreceptors.
True or False: The Primary Visual Cortex (PVC) is a biased map of the retina.
True, 50% of the PVC processes Foveal Signals (cortical magnification, center of image sharp) of which undergo Reorientation (correcting the flipped image projection on the retina).
Explain how On-Center Ganglion Cells in the Retina and LGN work.
There is an ON response (neuronal firing) whenever light is shined near the center of vision. There is also an Off-Surround when light is shone anywhere near the periphery (no neuronal firing).
Explain how Off-Center Ganglion Cells in the Retina and LGN work.
There is an OFF response (no neuronal firing) whenever light is shined near the center of vision. There is also an On-Surround when light is shone anywhere near the periphery (neuronal firing).
Explain the function of On Center and Off center cells.
Important in detecting contrasts and edges in image processing.
What are Simple Striate Cells in the PVC?
They respond best to edges in a particular position and orientation.
Monocular.
