Visual System Physiology Flashcards
what are the photoreceptor cells connected to?
bipolar cells
what are bipolar cells connected to?
ganglion cells
the central processes coming off the ganglion cells form what?
the axons of the optic nerve which eventually end up in the nuclei of the brain
which system is heavily dependent on convergence?
rod system
why is convergence important in the rod system?
it allows the rod system to operate in dim light
where does the density of the cones peak at?
the fovea
where does the density of the rods peak at?
about 20 degrees to the side of the cones
what happens to the photoreceptor cells under dark conditions?
they depolarize
what happens to the photoreceptor cells under light conditions?
they hyperpolarize
what are rods and cones constantly releasing?
glutamate
when is glutamate release from the photoreceptor cells the highest?
when it is dark
when is glutamate release the lowest?
when there is light
when does glutamate act as an excitatory amino acid?
when the receptor is an NMDA or non-NMDA receptor
when does glutamate act as an inhibitory amino acid?
when the receptor is an mGlu6 receptor
what glutamate receptor do bipolar cells express?
mGlu6 receptor
what does the mGlu6 receptor do when it is activated?
it closes the cGMP-gated Na+ channel
what happens when the bipolar cell is activated?
it releases glutamate
what glutamate receptor is found on the ganglion cells?
NMDA or non-NMDA (so glutamate will act as an excitatory amino acid on the ganglion cells)
what is the most prominent target of the retina?
the lateral geniculate body
what is the role of the lateral geniculate body?
it regulates the flow of information to the primary visual cortex
what is the role of the superior colliculus?
it creates a map of the visual space to activate appropriate motor responses required to move the eyes
what does the superior colliculus connect with?
connects with the tectospinal tract to send projections to cervical anterior horn cells
what is the pretectum important for?
the pupillary light reflex
what does the pretectum send projections to?
the edinger-westphal and then on to the ciliary ganglion
what are the small number of fibers that branch off the optic tract known as?
the retinohypothalamic tract
where do the fibers of the retinohypothalamic tract terminate?
in the supraoptic, suprachiasmatic and the paraventricular nuclei of the hypothalamus
visual input to the hypothalamus drives what?
the light-dark entrainment of the neuroendocrine function and other circadian rhythms
what is the role of the accessory optic nuclei?
advances visual processing
what are 4 functions of the lateral geniculate nucleus?
control the motions of the eyes-to converge on a point of interest, control the focus of the eyes based on distance, determine relative position of objects to map them in space, detect movement
what are the projections from the LGB to the visual cortex known as?
optic radiations
what 3 areas make up the visual cortices?
primary visual cortex, parastriate cortex, and extrastriate cortex
what is the major job of V1?
to identify the edges and contours of objects
what is area V2 important for?
depth perception, which is detected by analyzing the disparities between the two eyes
what is the major function of area V3a?
identification of motion
what is the major function of V4?
complete processing of color inputs
what are lesions in the V4 area known to cause?
achromatopsia- dullness in color
what are the MT/V5 areas important for?
tracking motion across a scene in terms of directionality and context of the background
what are the ocular dominance columns?
a slap of cells that preferentially respond to input from one eye or the other
what are the orientation columns?
an organized region of neurons that are excited by visual line stimuli of varying angles
where are the orientation columns located?
perpendicular to the cortical surface
what are the blobs in the primary visual cortex?
an organized region of neurons that are sensitive to color assembled into cylindrical shapes
what type of ganglion cells can directly sense light?
melanopsin ganglion cells
what are the melanopsin ganglion cells sensitive to?
blue-wavelengths of light
where do the melanopsin ganglion cells project directly to?
they project directly to hypothalamic suprachiasmatic nucleus
what is the suprachiasmatic nucleus?
it is the neuroendocrine effector in the pineal gland which produces melatonin in a rhythmic pattern
what is the general pathway of the dorsal pathway of the visual system?
from the primary visual cortex to the parietal/frontal cortex
what is the dorsal pathway important for?
associating vision with movement and completing motor acts based on visual pathway
what is the dorsal pathway laid out?
V1–> V2/V3–> V5/MT–> parietal lobe
what is the general pathway of the ventral pathway?
primary visual cortex to the inferior temporal cortex
what is the ventral pathway primarily responsible for?
interpreting images (recognizing human symbols, copying forms, facial recognition)
what is the ventral pathway laid out?
V1–> V2–> V4–> temporal lobe
