vision (dr maloney) Flashcards
three key functions of oculomotor system
- controls what we look at
- stabalizes image
- alignes both eyes
name all 7 oculomotor muscles
6 extra ocular muscles: superior oblique, inferior oblique, superior rectus, inferior rectus, medial rectus, lateral rectus
eyelid: levator palpabrae
what oculomotor muscles are inervated by the oculomotor nerve (III)
levator palpabrae, superior rectus, inferior rectus, medial rectus, inferior oblique
what cranial nerve controls the lateral rectus
abducens (VI)
what cranial nerve controls the superior oblique
trochlear (IV)
pupillary sphincter muscle (function)
makes pupile smaller
pupillary dilatory muscle (function)
dilates pupil
ciliary muscles (funciton)
bends/stretches lense (controlls focus)
rods (general info/what do you know)
- used in dark/dim light
- have low acuity
- monochromatic
- in the periphery
cones (general info/what do you know)
- used in bright light
- color vision
- have high acuity (most sharp/clear)
- concentrated in the fovia
- 3 types
retinal (def + function)
protein found on retina/photoreceptors that changes shape (conformational change) due to light
conformational change causes a chemical cascade: closes sodium ion channels which leads to depolarization. photoreceptors are active in the dark, inactive in light
when are photoreceptors depolarized and releasing neurotransmitter (glutamate)
in the dark
Photoreceptor cells are depolarized and constantly release the neurotransmitter glutamate. This is due to the presence of a molecule called cGMP, which keeps sodium channels open, allowing positive ions (Na⁺ and Ca²⁺) to flow into the cell. The continuous influx of ions keeps the photoreceptors in an excited state (depolarized), and they keep releasing glutamate, signaling to the downstream neurons (bipolar cells).
when are photoreceptors NOT depolarized and NOT releasing glutamate
in the light
when light hits the photoreceptor, retinal changes its shape, activating the protein opsin. This triggers a biochemical cascade which leads to the breakdown of cGMP. As cGMP levels fall, the sodium channels close, stopping the inflow of positive ions, causing the photoreceptor to hyperpolarize. This hyperpolarization reduces or stops the release of glutamate, altering the signal sent to the bipolar cells and ultimately leading to the perception of light in the brain.
summary (5 steps) of light transduced into neural activity
- photons hit retinal causing conformational change
- opsin (protein) changes shape in response to retinal conformational change
- other proteins change their interactions with opsin, triggering signaling cascade that leads to closure of ion channels
- voltage of photoreceptor changes and neuron stops releasing glutamate
- decrease in glutamate leads to responses (receptor potentials) in bipolar cells (both inhibition + excitation)
name the 4 opsins
Lopsin, Mopsin, Sopsin, Rodopson
what color are long wavelength cones (Lopsin/Lcone)
red
what color are medium wavelength cones (Mopsin/Mcone)
green
what color are short wavelength cones (Sopsin/Scone)
blue
how many types of cones do mantis shrimp have
12
how many photoreceptors in retina
~125 million photoreceptors
how many retinal ganglion cells in optic nerve
~1 million
the homunculus problem (def)
how do we actually UNDERSTAND visual information as opposed to simply being able to represent the visual information over and over in different areas of the brain and not really ‘getting anywhere’
how do we know who is who and how do we translate what we are seeing into having actual meaning for us
which cells are in the “horizontal path” in vision
horizontal cells, amacrine cells
which cells are in the “virticle path” in vision
rods + cones, bipolar cells, retinal ganglion cells
bipolar cells (in visual system) function
pool info from multiple photoreceptors (spacial summation)
amacrine cells function
larger scale lateral inhibition (than horizontal cells), adjust for light levels (switching btwn rods/cones), motion detection
horizontal cells function
lateral inhibition (comparing nearby points in space)
object detector (def)
sensory neurons that look to identify specific objects or stimuli that are relevant for that animal (fly detectors in frogs, faces in humans)
filter (def)
sensory neurons filter specific types of information on other parts of the nervous system (reduces redundancy)
efficient coding (def)
sensory neurons recode what we see in a more efficient way to reduce metabolic and physiological demand
3 principles of/for vision
- object detectors
- filter(s)
- efficient coding
who came up with the principles of vision
horace barlow
fovia (def)
place on retina with highest acuity (focus), highest density of cones accross retina (worse night vision)
true/false: opsins are g-couples proteins
TRUE!
what causes color blindness
lack of one or more of the opsins
the cone mosaic (def)
bayer filter (in digital cameras)
cones can’t be in the exact same space so we have a random mosaic of cones in our eyes
how many types of horizontal cells are there
two
what RGC type does fine detail
midget/parvocellular
retinal ganglion cells (RGC) def
outputs info from the retina into the brain (optic nerve)
what type of RGC does movement
direction selective RGCs
what type of RGC does large object tracking
parasol/magnocellular cells
what type of RGC does luminance
intrinsically sensitive retinal ganglion cells (isRGCs)
what type of RGC does color
bistratisfied/kinocellular RGCs
what structure in the brain is responsible for object detectors
superior colliculus
