Basics of Brain Development

Question 1

experience expectant

Answer 1

the brain adapts to the presence or absence of an experience that is typical human experience:

-during critical period in development
-all members of the species have the experience

Question 2

experience-dependent

Answer 2

individual differences in the brain organization and structural development from diferent experiences

-occurs through development

-reflects individual differences

Question 3

Steps in Brain Development

Answer 3

• The very beginning: Neurulation
• Taking shape: Encephalization
• The birth of neurons
• Migration of neurons
• Differentiation of neurons
  – Growth of axons and dendrites
  – Establishment of synapses
• Regressive processes
• Summary

Question 4

Neurulation

Answer 4

• Neurulation begins: end of the 3rd week
• The outer surface of the embryo,
  ectoderm, forms a neural plate at day 16
• It turns in on itself to form the neural groove

Question 5

Neurulation

Answer 5

• This deepens & fuses
  into the neural tube
• Separates
• Cells inside(the neural tube) give rise
  to the CNS
• Cells outside give
  rise to the ANS

Question 6

Encephalization

Answer 6

• By 4 weeks, the neural tube differentiates

into the 3 primary parts of the brain:
–forebrain (Prosencephalon)
–midbrain (Mesencepahlon)
–hindbrain (Rhombencephalon)
* And into the spinal cord
* At the same time, it is curving

Question 7

neuron

Answer 7

they create networks that allows information to pass through the brain

Question 8

glia

Answer 8

makes possible for neurons to survive,make network and send information effectivaly

they play a role in neuron migration

Question 9

Neurogenesis

3rd week to adulthood

Answer 9

• From the inside of the neural tube, the ventricles form(ventricular zone) - disolves later on
• From the outside, neurons and glial cells form
• Different kinds of neurons born from different areas

along the neural tube
* Each neuroblast appears to clone a set number of neurons

• Intrinsic factors signal cloning to begin & end
• Neuorgenesis actually continues across life
• mostly done pre-natal
  – Definitely in hippocampus, olfactory bulb
  – Once thought in other areas of cortex –not so sure
• Diet, exercise, many factors influence

Question 10

Migration of cells

Answer 10

• Passive & Active Migration
• Genetic & neurotrophic factors guide
• Active migration aided by radial glial fibers
• End point “recognized”, and migration stops

Question 11

neuron migration

4-6 week of conception

Answer 11

• neurons are creted in the ventricular zone and they migrate to other parts of the brain
• Active cell migrations assisted
  by Glial cells that acts as guides for the neuros
• The neurons can use those to
  guide their journey

Question 12

Cell Migration: Inside Out

Answer 12

• First layer 1 is laid down, then the rest is inside out
• The cortical plate will become the deep layers of the cortex, V & VI
• Later born neurons migrate radially into the cortical plate, through V & VI, and
  become layers IV - II
• Thus each group of migrating cells must pass through the layers already laid down by the earlier arrivals

Question 13

neurons creation

Question 14

Growth of Axons: Intrinsic processes

Answer 14

• Axons grow & reach specific destination
• This controlled by signaling molecules that act to attract or repel growing axon (e.g.,
  cell adhesion molecules; nerve growth factors).
• Axons gradually become myelinated (more later)

Question 15

Growth of Dendrites:Intrinsic properties

Answer 15

• Dendrites grow & branching increases
• Dendritic sprouting begins around prenatal week 15 (about same time axons reach the cortical plate)
• Between prenatal weeks 25 and 27, dendritic spines appear

Question 16

synaptogensis

20 weeks- early adulthood

Answer 16

creating connection between neurons

create synapses which is done by dentrites growing and axons growning and synapses (what connects them form)

Question 17

Myelination

Answer 17

• Myelin is lipid/protein substance
  – Oligodendroglia produce myelin in CNS
  – Schwann cells produce myelin in ANS
• Myelin wraps itself around axon as form of insulation.
• Myelin speeds conduction velocity
• Myelination has implications for both serial and parallel processing (e.g., multitasking).
• as well as controls jerky movements

Question 18

Myelination

Answer 18

• Myelination beginning
  prenatally into young adulthood
  (and in some regions, as “late” as middle age).
• Starts in primary sensory areas prenatally, then to brain stem, cerebellum, and corpus
  collosum in first year postnatal
• **formation of fatty sheafts on axons that support long-term connectivity between areas
  **

Question 19

Overproduction:
a principle of neural development

Answer 19

• Both axons and dendrites continue to develop into second postnatal year
• There is an initial overproduction of axons and dendrites followed by retraction
• And an initial overproduction of synapses
• Overproduction and pruning an essential step in establishing organization

Question 20

What causes regressive
processes?

Answer 20

• Some paring back is signaled by genetics
• But most pruning is the result of competitive processes
  – those synapses that are used become more efficient
  – those cells and synapses that are not used become silent, atrophy, or die
  – allows for the establishment of optimal circuitry

Question 21

synaptic pruning

age 2 to adolecence

Answer 21

the loss of synapses due to lack of use

Question 22

plasticity

Answer 22

development is not fixed in biology program rather it adpts to enviroment and experiences

Question 23

Effects of Experience

Answer 23

Effects of Experience
* More dentrites with
enrichment

• More synapses
• Some maintained, i.e.
  less pruning
• Others established
  through learning
• Not all pruning bad –
  think of competitive
  processes that optimize
  organizationEffects of Experience
  *

Question 24

Social policy issues

Answer 24

• Early home environment and brain
  development: experience expectant
  processes more permanently impacted
• Family, school, neighborhood –
  resources available
• Different kinds of enriching experiences
• Forms of intervention?

Question 25

Experience Expectant & Dependent

Answer 25

* Experience-expectant (Greenough)
– Development based on the expectation that
appropriate environments will provide information
needed to select appropriate subsets of synaptic
connections. Common to all members of the species
(examples: all human have two eyes;
language; attachment)
– Lasting impact (critical/sensitive period)

• Experience-dependent (Greenough)
  – Unique to each individual, it most likely involves active
  formation or strengthening of synaptic connections
  throughout the life span based on each person’s
  interaction with his/her environment. 5
  – Can be changed