brain facts chap 6 ; the developing brain

in development, neurons that arrive latest make the (deepest/outermost) layer of the cortex

outermost

what are 6 stages of neural development

proliferation, migration, differentiation, synaptogenesis, apoptosis, and rearrangement

what initiates the formation of immature nerve cells

signaling molecules turn on certain genes and turn off others

what happens during proliferation

the pool of early stage brain cells increases by billions

what happens during migration in neural development

newly formed neurons travel to their final destinations

name the three layers that emerge during the very early stages of embryonic development

the ectoderm (outer-most layer), mesoderm (middle layer), and endoderm (inner-most layer)

what induces the development of specific cell types in very early stages of embryonic development

signals produced by surrounding tissues turn certain genes on and others off

what is neural induction

the process in which signals from the mesoderm trigger some ectoderm cells to become nerve tissue

what singaling molecule, secreted by mesodermal tissue lying beneath the developing spinal cord, causes exposed neurons to convert into a specialized class of glia

sonic hedgehog

the fate of a developing cell is largely determined by what

its proximity to various sources of signaling molecules

the concentration of each type of signaling molecule decreases farther from its source, creating what

gradients of signaling molecules throughout the brain

sonic hedgehog secreted by mesodermal tissue lying beneath the developing spinal cord causes exposed neurons to convert into what

a specialized class of glia

describe what happens when neurons are exposed to sonic hedgehog secreted by the mesodermal layer lying beneath the developing spinal cord in high concentrations, medium concetrations, and low concentrations

exposure to high concentrations makes neurons turn into a specialized class of glia, medium exposure makes neurons turn into motor neurons, and low exposure results in interneurons

what are neural stem and progenitor cells

special cells that can divide and become a variety of mature cell types

in the embryo, neurons arise from a fairly small pool of what two types of cells

neural stem and progenitor cells

what is the main difference between early divisions of the initial neural pool of cells and later divisions in embryonic development

early divisions are symmetric, meaning the split results in two identical daughter cells that both keep dividing. later divisions become more asymmetric, meaning that perhaps only one daughter cell keeps proliferating while the second progresses toward its ultimate cell fate as a neuron or glial cell

how fast is proliferation of the brain in early development (how many cells in how much time)

billions of cells are produced in a matter of weeks

describe the concentration of neural stem cells and progenitor cells in the brain during adulthood. What does this mean

there are only a few neural stem and progenitor cells left in the brain in adulthood, meaning neurogenesis is limited to a few regions of the brain

when during gestation does the human brain begin to form

after three weeks

protein defects causing a premature switch from symmetric to asymmetric divisions in embryonic development may result in what

microcephaly

what is microcephaly and what errors during embryonic development might cause it

microcephaly is a disorder characterized by a severe reduction in brain size. It could be caused by a premature switch from symmetric division to asymmetric division in the nervous system during embryonic development

what could excessive proliferation of brain cells lead to

megalencephaly

what error in embryonic brain development might cause megalencephaly

excessive proliferation

what is megalencephaly

disorder where you have a very large and heavy brain

what is pattern separation

the ability to discriminate between similar memories

what brain area is most important in pattern separation

the dentate gyrus

how long after conception does migration begin

three to four weeks after conception

what happens to the ectoderm 3 to 4 weeks after conception

it starts to thicken and build up along the midline of the embryo

ectoderm overlying the notochord thickens to form what in embryonic development

the neural plate

what happens within a few days of the development of ridges on the neural plate

the ridges fold toward each other and fuse into a hollow neural tube

what happens to the head end of the neural tube

it thickens into three bulges which form the hindbrain, midbrain, and forebrain

when do the first signs of the eyes and the hemispheres of the brain appear in human gestation

at week 7 in humans

in ~week 7 of gestation in humans, where do newly produced neurons move from and to where

they move from the neural tube's ventricular zone, which lies along the inner surface of the tube, toward the border of the marginal zone, or outer surface.

what do neurons do after they stop dividing in human gestation

they form an intermediate zone where they gradually accumulate as the brain develops

what happens at the intermediate zone in neural development as the brain develops

neurons gradually accumulate

what guidance mechanism accounts for 90% of neural migration in humans

radial glia

what is the function of radial glia in migration during neural development

neurons use radial glia as scaffolding to reach their final destinations

during brain development where do radial glia project from and where to

they project radially from the intermediate zone to the cortex

what is radial migration in neural development

migration of neurons on radial glia

in development, neurons that arrive earliest make the (deepest/outermost) layer of the cortex

deepest

in neural development how is migrating sideways or tangentially (parallel to the brain's surface) different from migrating radially

migrating tangentially uses a different mechanism than radial glia

what are some external factors that can prevent proper migration

exposure to alcohol, cocaine, radiation, etc.

what can misplacement of cells during migration result in

intellectual disability or epilepsy

mutations in genes that regulate migration in neural development have been shown to cause what

rare genetic forms of intellectual disability and epilepsy in humans

what is the difference between neural developmental stages like induction, proliferation, and migration and later stages

induction, proliferation, migration, and similar stages happpen internally during fetal development, but later phases of brain development depend increasingly on external experience

what kind of factors influence the connections formed by neurons after birth

factors such as listening to a voice, watching a mobile spin, and proper nutrition

where are the longest human axons found

in the periphery, extending from the lower spinal cord all the way to muscles in the toes

how many times longer than the diameter of the corresponding soma can an axon be in humans

up to 1,000,000 times longer

what is the growth cone of an axon

an enlargement at the tip of the axon that actively explores the environment to seek out its precise destination

how does the axon of a neuron grow

by the extension of its growth cone

how is a growth cone guided to its final destination

it is guided by molecular cues in its environment

are growth cone guiding molecules studded on the surface of cells or secreted into areas near the growth cone

both

how can the growth cone respond to environmental molecular cues

it has receptors that the molecules bind to

what is the function in the nervous system of the netrin, semaphorin, and ephrin families of proteins

they are signaling molecules that provide guidance to the growth cone as the axon grows

describe the way that attractive and repulsive signals work together to guide the growth cone to its destination

Attractive cues lay a path growth cones follow, while repellent molecules funnel growth cones through precise corridors

are growth cone guiding molecules similar across many species or characteristic of humans

similar across many species

how are growth cone guiding proteins different in flies or worms from in mammals like humans

they are smaller in flies or worms, but have very similar functions

where was netrin first discovered and what was it doing there

it was first discovered in a worm, where it was used to guide neurons around the worm's nerve ring

what proteins guide developing axons around the mammalian spinal cord

netrins

how does a neuron respond to input at thousands of synapses

the combined effects of cues from these synapses ultimately determine how a receiving neuron responds

besides intial guiding of the growth cone to a final destination, how can specificities of what neuron connects to what be made

additional molecules mediate target recognition when the axon reaches the proper location

how is the synapse anchored together

both sides of the synapse produce proteins that span the synaptic cleft and connect the neurons

in relation to synaptic vesicles, what must the terminal of an axon do to become specialized for releasing neurotransmitters

it must stockpile itself with proteins that enable vesicles to be held in place and then released

what has to happen on the postsynaptic side of a synapse for a synapse to function properly

receptors that respond to neurotransmitters must cover the membrane

how do astrocytes regulate synaptic development

they secrete molecules that regulate aspects of it

what happens to the amount of synapses between neurons in a culture dish when there are no astrocytes in the dish

some neurons only form a few synapses

many synapses in the brain are contacted by what

astrocytes

how many synapses can one astrocyte influence

thousands across multiple neurons

what might underlie the degradation of synapses that occurs during aging

the loss of certain synapse promoting molecules

it is thought that defects in synapse promoting molecules could underlie disorders such as what

autism

what determines what type of neutransmitter a neuron will use to communicate

an array of various signals

what type of neurotransmitters can motor neurons use and can this vary

they can use acetylcholine, and that doesn't vary, all motor neurons use acetylcholine

when certain immature neurons are maintained in a culture dish with no other cell types, they produce the neurotransmitter \_________. In contrast, when the same neurons are cultured with specific cells, such as cardiac tissue, they produce the neurotransmitter \_________

norepinephrine, acetylcholine

Many researchers believe that the signal to engage the gene, and therefore the final determination of the chemical messenger a neuron will produce, is
influenced by factors that come from the location of the synapse itself. (this isn't a question, just know this)

:)

what is saltatory conduction

saltatory conduction is the "jumping" of an action potential between the unmyelinated nodes of ranvier

how many times faster can a neuron with myelin transmit signals as compared to the same neuron without myelin

as much as 100 times faster

when does formation of myelin occur

throughout the lifespan

why do neurons use saltatory conduction

it makes the signal travel faster

what percent of neurons formed during development survive to adulthood

50%

what is apoptosis

programmed cell death

what is paring back

the process by which the initial neural network is decreased in number of neurons, creating a more efficient system

when does apoptosis occur in neurons

when the neuron fails to receive enough trophic factors from its target tissues

what are trophic factors

chemical signals that prevent apoptosis in neurons

where are trophic factors made

in the target tissues of a neuron

what is the difference in function of different types of trophic factors

each different type supports a distinct type of neurons

what does nerve growth factor important for

it prevents apoptosis in sensory neurons

how far into the lifespan of a human does apoptosis occur

until death

how can apoptosis be a bad thing in neurons

neurodegenerative diseases can activate apoptosis inappropriately

do excess neurons in early development form synapses

yes. An excessive amount

in primates, neural projections from the two eyes to the brain have what issue

they overlap

describe the amount and concentration of synapses in a young primate's cerebral cortex vs an adult's

there are more of them and they are about twice as concentrated in the young primate

what is pruning

the process by which unused connections in the brain atrophy and die

what is pruning heavily dependent on

the relative activity of connections

in relation to the activity level of synapses, which synapses are pruned and which survive

synapses with a lot of activity survive, those without are lost

how do astrocytes aid in formation of eye-specific connections

they engulf and eliminate unnecessary synapses