Visual system physiology Flashcards
What is cones and rod mediated vision and what happen if you lose them
Rod mediated vision is called scotopic vision
-lose you have night blindness
cone mediated vision is photopic vision
-lose you are blind
What is mesopic vision
Vision that occurs when both rods and cones are activated by the light levels of the environment
convergence of cells for rods
Rods need one photon and multiple rods converge onto a single bipolar cell which contact a single macrine cell
-allows for the highest levels of sensitivity but lower resolution
Convergence of cells for cones
Need 100 photons to respond
One cone directly contacts one bipolar cell
this allows for best resolution but low sensitivity
Dark Current
Gutamate release is highest when it is dark which leads to depolarization
this is because for rods, photons act as a hyperpolarizor of the cell
What types of potentials do Neuronal cells use
Graded potentials rather than Action potentials
therefore the varying streams of glutamate lead to various degrees of neurotransmitter release
not binary
ON-center bipolar cells
Activation of a photoreceptor in the center of this bipolar cells receptive field causes depolarization of this bipolar cell
contains a glutamate receptor called mGluR6 which is a Gi GPCR receptor
glutamate binds to the mGluR6 receptor that decreases cation influx by closing cGMP-gated Na+ channels
high levels of glutmate closes the channel and the ON-center bipolar cell remains inactive
Low levels of glutamate allows the channel to be open nd the ON-center bipolar cell will depolarize
works with light
OFF center bipolar cells
Activation of a photoreceptor in the center of this bipolars cell receptive field causes hyperpolarization of this bipolar cell
express ionotropic receptors for glutamate (non-NMDA) AMPA that when glutamate is present it binds the receptor and the ion channel opens and the cell will depolarize
works at night
Ganglion cell
If the associated bipolar cell is depolarized it releases glutmate on to the ganglion cell to depolarize it
-contain NMDA or Non-NMDA receptors
Ganglion cells use Action potentials rather than graded potentials
become the optic nerve and release glutmate at the cortex
Amacrine cells
inhibitory and release GABA or glycine
suppresses nearby activity
important in allowing to see in low light conditions to enhance edges, shadows, and contrasting areas of luminance
Lateral Genticulate body
Direct target of the retina
Control the motions of the eye to converge on a point of interest
control focus of the eyes based on distance
Determine relative position of objects to map them in space
Detect movement relative to an object
Suprior Colliculus
Creates a mp of visual space to activte appropriate motor responses required to move the eyes into their intended position within the orbits
coordinates head and eye movement to visual targets
Pretectum
Reflex control of pupil and lens, sends projections to Edinger-Westphal then on to ciliary ganglion
Hypothlamus
Small number of fibers branch off the optic tract, forming the retinohypothalamic trct and terminate in the supraoptic, suprachiasmatic and paraventricular nuclei of the hypothalamus
visual input to the hypothalamus drives the light-dark entrainment of neuroendocrine function and other circadian rhythms
Medial Temporal area
Contains neurons that responds selectively to the direction of a moving edge
tracks the motion across a scene in terms of directionality and background/foreground context
ignores color
also called V5
Accessory optic system
Consists of several small nuclei
advanced visual processing
important role in eye movements of compensation and pursuit, particularly in alternation with saccadic-type eye movements responding to prolonged watching of large field motion
Primary Visual Cortex
V1 (striate cortex)
Constructs local image features including size, shape, orientation local direction of movement, and binocular disparity
Mostly excitaatory and has some GABAnergic interneurons
Identify the edges and contours of Objects
Visual association cortex V2
V2 (extrastriate)
Depth perception occurs by analyzing the disparities between the two eyes
Visual association cortex V3a
Identification that motion is occuring
Visual association cortex V4
Complete processing of color inputs
Visual association cortex V5
Medial Temporal Area
identifies the direction of a moving edge in terms of context with background and foreground
Ocular dominance columns
Found in the primary visual cortex
A slab of cells that preferentially respond to input from one eye or the other
are found in stripes
Orientation columns
Found in primary visual cortex
organized region of neurons that are excited by visual line stimuli of varying angles
Orientated perpendicular to the cortical surface
mapped in swirls
Blobs
Found in the primary visual cortex
Organized region of neurons that are sensitive to color that assemble into cylindrcal shapes
All 3 color coding cones are required for accurate color detection
Achromatopsia
Three types of cones in the retina function normally
but damage to specific extrastriate cortical areas that render patients unable to see information supplied by the retina
Color blinding
Improper function at the level of the cones
Melanopsin ganglion (MG)
Photosensitive ganglion that project directly to the suprachiasmatic nucleus of the hypothalamus, the light sensitive nucleus of the pretectum and the limbic system
does not project to the visual cortex so it is called the non image light responsive system
play a role in regulation of circadian rhythms, sleep, and mood
Ventral pathway
V1 to V2 to V4 and then to the Temporal lobe (what pathway)
involved in interpreting images (reckognizing or copying shapes, forms, faces, and complex patterns)
selectively activated by shape color, texture, and object recognition
face recognition is specialized area
Dorsal Pathway
V1 to V2, V3 to MT/V5 and then to Parietal lobe (where pathway)
Primary pathway with associating vision with movement
also complete motor actions based on visual input through this pathway
selectivity activated by directionality and speed of movement
Agnosia
see an object but is either unable to copy or identify what it is. Cant see parts of an object contributing to a whole or cannot interupt, understand, or assign meaning to the object
inabillity to construct or draw visual stimuli or they cannot recognize a picture of an object
damage to the temporal lobe and interruption of the ventral pathway
Prosopagnosia
A type of agnosia that results in the abillity to identify a face as a face, recognize its parts, and detect facial expressions indictative of emotion but cannot recognize a particular face as belonging to a specific person
damage to the temporal lobe and interruption of the ventral stream
