Development of the Nervous System

just stuff learned until exam 1

why can’t some behaviors not be displayed

nervous system needs to be developed enough to support them

what do environmental influences on development often require first

nervous system change

what do many developmental disorders involve

a deviation in nervous system development

zygote

fertilized ova, cells dividing

morula

solid ball of about 100 cells

blastula

the morula starts to form a cavity which fills with fluid and turns into a solid ball

gastrulation

blastula gets bigger and then inverts/collapses in on itself and pushes in

gastrula

forms body layers that eventually become layers of our body

what are the three layers of gastrula

endoderm, mesoderm, ectoderm

what does the endoderm become

internal organs

what does the mesoderm become

bones, muscles, circulatory system; middle of our body

what does the ectoderm become

skull, nervous system, skin

notochord

primitive temporary structure that tells the ectoderm what to become; driver of early development, induces cells of the ectoderm above it to become primitive nervous system

where is the neural plate and neuroepithelium

right above the notochord

how is the neural tube formed

neural plate folds into the neural groove, edges push upward to the groove, edges of the neural plate move and touch each other

neural tube

where all the cells of the brain get developed

when does human neurulation start

around day 21, ends by day 28

what are some issues that can happen from improper neurulation

anencephaly, spina bifida

anencephaly

complete normal production of the spinal cord, but deviation in the neural tube closure at the front; empty space because the neural tube hasn’t closed at one portion of the neural axis, cells float into the embryonic space and there is no cortical tissue because neural tissue didn’t capture it

spina bifida

causes rupturing of a cavity and CNS tissue comes out of the spinal cord

neurogenesis

cell birth

where does neurogenesis happen

inside surfaces of neural tube

ventricular zone

cells that line the inside hole of the neural tube, gives rise to new cells

neuroepithelial cells

the progenitor cells in the ventricular zone that differentiate into neurons and glial cells.

how can we see neurogenesis in dividing cells

natural thymidine and man-made BrdU

thymidine

a nucleoside that incorporates into DNA during replication and is used to measure cell division, new DNA incorporates it

BrdU

tricks cells into incorporating it into their new DNA because it’s similar to thymidine; when you inject it into an animal it tricks cells into thinking it’s thymidine and can track cell division

what does BrdU allow us to see

can see cells’ birth place if sacrificed earlier, can see the cells’ final place if sacrificed later

what is an example of neurogenesis occurring after birth

male birds showing another wave of it during the breeding season when testosterone was high, and if the birds were castrated there was no song; forcing females to sing gave them testosterone and after a few weeks neurogenesis was seen

what brain systems produce new neurons

olfactory bulb, amygdala and hypothalamus, hippocampus, cerebral cortex

what is an example of neurogenesis in the olfactory bulb

mother rats giving birth and being interested in their pups when they weren’t originally; changes the valence of the scent cues from the pups

how is neurogenesis shown in the hippocampus

when learning something, once those cells become incorporated they become firmed/concreted

what does inhibiting neurogenesis in the hippocampus lead to

blocks learning

what is neurogenesis in the hippocampus reduced by

stress

cell migration

critical part of putting the nervous system together, how cells get to the right layer that each have different functions

radial glia

helps cells know which layer to go to during migration; structural cells that form a scaffold through the early brain that allow newborn cells to latch onto and the cells slither up the scaffolding and pull themselves along until they find their resting spot, can allow them to travel in any direction

where are neurons born

in the inner layer

how do cells know when to stop moving along the radial glia

the time the cells are born dictates where they’ll be in the layers; earliest neurons have genes that express that they should stop at an early layer, and the same thing applies to other layers/cells

what is a case where layering/age effect doesn’t apply properly when it comes to radial glia

weaver/reeler mice

what happens to weaver/reeler mice

the gene to make radial glia is mutated, they have the same number of neurons but they’re not in the same layered structure, learning/functioning isn’t the same

what do cells use after radial glia is used/refines where cells wind up after radial glia

somal translocation

what does somal translocation involve

cell/young neuron elongating what becomes its axon and gripping onto extracellular structures and pulling itself forward

what do types of cells differ in

morphology (shape), receptors (dopamine, gaba, progesterone, etc), neurotransmitters

how is cell differentiation determined

genetically, local molecules near cells

where are differentiating factors that determine what a cell will become

throughout the neural tube

what molecules in the developing brain are released by glial cells

guidance cubes and growth factors

guidance cube molecules

tell a growth cone to stop as it gets closer

what are growth cones looking for

growth factors, guidance cubes that say stop and don’t go that way and others that attract them

what are the two types of molecules that guidance cues and growth factors can be

substrate bound and diffusible

substrate bound

mostly detected only when growth cone is very close, glia around the target cells is confirming it’s correct, cells that make these are released in very small distance if not stuck to the cell itself

diffusible

detectable at a distance, but strength is influenced by concentration gradient, growth cone is expected to get closer to the target based on diffusion, leads growth cone to the substrate bound

attractant

growth cone sniffs it out and extends itself toward this kind of glial cell, it’s a good match, growth cone hones in on it

repellent

tells growth cones to move away, it’s going in the wrong direction

collapse

if growth cones are going in the direction of glial cells making repellents and can’t find what they want they collapse; pushed the axon into an environment that doesn’t have a corresponding attractant

growth permissive

keeps growth cone highly regulated, leads the growth cone down a path of sorts using attractants and repellents

follower neurons

once enough pioneer neurons have made the pathway, the use the attractive cue then just follow the same pathway/axons of the pioneers, just need to find axons of the cells that have already found the target until their own growth cone verifies they’re supposed to be there

what happens after the growth cones reach where they’re going

terminal button is formed

how do terminal buttons form

axons branch out and growth cones start to develop bumps

maturation

end of presynaptic cell connecting with postsynaptic, formation of mature synapse, connection between the two becomes functional, the cell now has the capacity to make, package, and release neurotransmitters into the synaptic gap

synaptic pruning

the process by which excess neurons and synapses are eliminated to optimize neural connections and improve efficiency in the nervous system.

when are most human synapses made by

around 2

why is synaptic pruning critical

a cell has made it to the target, but if it wasn’t correct, the synapse dies/cell dies, and it’s pruned; if the target was correct but wasn’t healthy, can’t feed the presynaptic cell

why do synaptic connections slow down

the environment tells the brain what is necessary to keep and what isn’t, there is a metabolic cost to keeping all of the cells, use it or lose it

why are dendrites rough

they contain nubbins called dendritic spines

where do presynaptic axons and terminal buttons touch

dendritic spines

what do the bumpy dendritic spines allow for

better latching on, more surface area (more space for incoming axons to make a synapse)

synaptic connection with which type of dendritic spine is the weakest

filopodium

what does the mushroom dendritic spine communicate to the synapse

it’s stable, they’re staying put

when do synaptic nubbins start to go away

adolescence