Visual System Physiology Flashcards
Photoreceptor cells are connected to?
Bipolar cells
Bipolar cells are connected to?
Ganglion cells
What cell’s axons form the optic nerve?
Ganglion cells
Where does the amount of rods peak?
20 degrees off center
Where does the amount of cones peak?
At the center - fovea
Cones are used for?
Color detection and visual acuity
Rods are used for?
Light detection and have a high sensitivity
Darkness does what to the photoreceptor cells?
Depolarizes
If a photoreceptor is depolarized, what will it release to the bipolar cell?
LOTS of glutamate
If LOTS of glutamate is released to a bipolar cell, what receptor will it bind?
mGLUR6
What is the action of mGLUR6?
It closes cGMP-gated sodium channels = bipolar cell is inhibited!
Light does what to the photoreceptor cells?
Hyperpolarizes
If a photoreceptor is hyperpolarized, what will it release to the bipolar cell?
LOW amounts of glutamate
If LOW amounts of glutamate are released to a bipolar cell, what happens?
The bipolar cell will spontaneously depolarize
If a bipolar cell depolarizes, it will release ____ to the ganglion cell and _____ it
Glutamate
Depolarize
What neurotransmitter do ganglion cells release?
Glutamate
What type of glutamate receptor does the ganglion cell have?
Normal - NMDA or non-NMDA that work to excite the cell with glutamate
What is the rate of glutamate release from photoreceptor cells?
Constant - only the amounts are changeable
What are some direct targets of the retina?
LGN Superior colliculus Pretectum Hypothalamus Accessory optic nuclei
Converge eyes to a point, controls focus, detects movement, maps position of objects around you
Lateral Geniculate Nucleus
What are the physiologic areas in the visual cortex?
V1, V2, V3A, V4, MT/V5
V1’s job?
Identify edges and contours of objects
V2’s job?
Depth perception
V3A’s job?
Identify motion; as in did it happen or not? - no processing
V4’s job?
Complete processing of color inputs
MT/V5’s job?
Tracks motion across a scene in terms of directionality and context of background
Lesion of V4 can result in?
Achromatopsia
Achromatopsia
Problems seeing color especially if lesion is bilateral
What is the organization of things in the 6 layers of the visual cortex?
Ocular dominance columns, orientation columns and blobs
What do ocular dominance columns respond to?
Input from one eye or the other
Ocular dominance columns and orientation columns run _______ to each other
Perpendicular
Neurons in an orientation column are excited by?
Visual line stimuli of varying angles depending on the column
Neurons in blobs are sensitive to?
Color
What shape are blobs?
Cylindrical that drill down into the cortex
Do ocular dominance columns, orientation columns and blobs span all layers of the visual cortex?
YES
What are MG cells?
Melanopsin Ganglion cells
What is special about MG cells?
They can directly sense light, specifically blue light
What do MG cells help to regulate?
Circadian rhythm
Where do MG cells project?
Hypothalamic suprachiasmatic nucleus in the pineal gland that releases melatonin
Non-image-forming light responsive system?
Melanopsin ganglion cells
Patient’s who are blind due to photoreceptor cell loss still have what?
MG cells, and thus are responsive to some blue light and have a circadian rhythm
Where is the lesion if a patient is blind and lacks a circadian rhythm?
CN2 –affects all cells in the retina
Why do older people experience sleep issues?
Their lens becomes more yellowish and decreases blue light transmission throughout the day
Blue light exposure before sleep can _____ sleep
Disrupt
Can treat seasonal depression, increase alertness and stimulate cognition
Blue light
This pathway is the primary path for associating vision with movement
Dorsal pathway
Dorsal pathway completes?
Motor acts based on visual imput
What is the dorsal pathway steps?
V1 - V2/V3 - MT/V5 - Parietal lobe
This pathway is the pathway that interprets images
Ventral pathway
Ventral pathway recognizes?
Shapes, forms, faces
What is the ventral pathway steps?
V1 - V2 - V4 - inferior temporal lobe
What areas in the temporal lobe have their own area, thus if one is damaged the others may not be?
Copying objects, naming objects and facial recognition
