chapter 23 Flashcards
what extends from the growth cone to guide the developing axon toward its proper destination
filopodia
the entire nervous system develops from the..
ectoderm
once a cell commits to a type of glial cell, will it be able to divide again
no
trimester and neron development
1st-neurogenesis
2nd-migration
3rd-differentiation
how do pioneer axons find their target in the developing human brain
other neurons give chemical signals, either chemoattractents or chemorepellents
ocular dominance
binocular organization of the cortex
monocular deprivation
one eyelid is sealed closed shortly after birth
open eye columns expand in width while closed eye columns shrink
how is monocular deprivation reversed
closing the previously opened and opening the previously closed-this is called reversed occulusion
critical period for ocular dominance
last until 6 weeks of age
what does the establishment of binocular receptive fields depend on
correlated patterns of activity that arise from the two eyes as a consequence of vision
binocular vision
vision using two eyes with overlapping fields of view, allowing good perception of depth.
types of vergence
convergence and divergence
convergence
coordinated contraction of both medial rectus muscles brings both eyes toward the midline (ie, the nose)
divergence
coordinated contraction of both lateral rectus muscles brings both eyes toward the periphery
our vision vs rats vision
our vision is convergent, so we have good depth perception. rats eyes are divergent so it can see further behind
where can ocular dominance shifts occur
in all mammals that have binocular vision
binocular competition
inputs from two eyes actively compete for synaptic control of post synaptic neuron
if activity of two eyes is correlated and equal in strength, the two inputs will be retained on the same cortical cell
if balance is disrupted by depriving one eye, the more active input will somehow displace the deprived synapses or cause them to be less effective
ocular dominance columns
are stripes of neurons in the visual cortex of certain mammals (including humans) that respond preferentially to input from one eye or the other
is visually driven retinal activity sufficient for modifications of binocularity?
no, it requires for one to pay attention to visual stimuli and use vision to guide behavior
ex-if animal is kept anesthetized, even though cortical neurons respond briskly, synaptic plasticity requires the release of “enabling factors” that are linked to behavioral state such as attention
rules for synaptic placticity
neurons that fire together wire together
neurons that fire out of sink lose their link
what does it mean by neurons that fire together wire together
if presynaptic neuron is active and postsynaptic neuron is strongly active under the influence of other inputs, the dynapse of the presynaptic anxon is strengthened
what does it mean when neurons that fire out of sync lose their link
when presynaptic axon is active and post synaptic neuron is weakly activated by other inputs the synapsed formed by the presynaptic axon is weakened
optic chiasm
visual signals from the left hemifields of both eyes are sent to the right hemisphere of the brain, while the signals from the right hemifields of both eyes are sent to the left hemisphere of the brain
So each hemisphere of the brain is responsible for processing the visual information in…
opposite visual field from both eyes
