How does the nervous system develop?

Question 1

what are the 3 approaches to development of brain and behaviour?

Answer 1

1. emerging brain structure correlates with emerging behaviour
2. Emerging behaviour correlates with changes in brain structure
3. factors influence both behaviour and brain development

Question 2

What is an example of emerging brain structure correlating with behaviour?

Answer 2

myelination of motor cortex + increased complexity of grasping in infants

Question 3

what is an example of emerging behaviours correlating with changes in brain structure?

Answer 3

increased complexity of language + cortical thickening of language areas

Question 4

What is an example of factors that influence both brain and behaviour development?

Answer 4

Exposure to alcohol prenatally and impaired brain and behaviour development

Question 5

What are the 3 stages of prenatal development?

Answer 5

Germinal stage (conception-3wks)
Embryonic stage (3wks-9wks)
Foetal stage (9wks-birth)

Question 6

What happens from conception-3wks?

Answer 6

0-2wks - zygote travels down fallopian tube to uterus
cells multiply rapidly and differentiate as they multiply
Ectoderm thickens and becomes the neutral plate by day 8 of gestation. The sphere of dividing cells flattens

The neural plate folds to form the neural groove, which then closes over to form and a fluid-filled cylinder - the neural tube

Question 7

What is a neural tube defect?

Answer 7

Anencephaly - neural tube fails to completely close over
underdeveloped skull and brain - life-limiting condition
5-10000 births

Question 8

what happens from wk4-birth?

Answer 8

Embryo: up to 10wks

Foetus: wk10-birth

By week 4 -main divisions of CNS are formed:
- forebrain
- midbrain
- hindbrain
- spinal cord

By mid pregnancy, cerebral hemispheres have expanded to cover the rest of the brain

By 6 months, cell proliferation —> infolding —> sulci and gyri on surface of cortex. Lobes can be differentiated

Question 9

What are the 7 stages of nervous system development?

Answer 9

1. cell birth - neurogenesis
2. cell migration
3. cell differentiation
4. cell maturation
5. synaptogenesis - formation of synapses
6. cell death and synaptic pruning
7. myelination

Question 10

what happens during cell birth(neurogenesis)?

Answer 10

non-neuronal cells divide by mitosis to produce neurons
Single layer of cells along inner surface of neural tube –> ventricular zone (all neurons and glial cells come from there)

Question 11

What happens during cell migration?

Answer 11

Newly formed cells move from the ventricular zone to the correct destination in the nervous system

Travel along radial glial cells which act as guides

Cells move to establish distinct nerve cell populations (e.g., layers of cerebral cortex)

Question 12

What happens during cell differentiation?

Answer 12

Cells reach their destinations and start to express particular genes

Cell-cell interaction coordinates development – ensures right type of neuron for that part of the brain

Cells acquire distinctive characteristics – e.g., neurons – as the result of expressing particular genes

Question 13

What happens during cell maturation?

Answer 13

dendrite and axon growth

Question 14

What happens during synaptogenesis?

Answer 14

Formation of synapses - neurons extend their axons and dendrites and form many synapses with one another.
continues after birth

Question 15

What happens during cell death and synaptic pruning?

Answer 15

‘use it or lose it’: synaptic connections that do not become part of a functional neural network are lost

synaptic pruning/rearrangement and maturity proceed at different rates in different brain areas

Cell death aka apoptosis – ‘surplus’ cells die

Question 16

What happens during myelination?

Answer 16

• axons become wrapped in fatty sheath

speeds the conduction of electrical signals
Some prenatally; rapid shortly after birth; continues into adulthood

Question 17

What factors influence brain and behaviour development?

Answer 17

Intrinsic and extrinsic factors

Question 18

What are intrinsic factors?

Answer 18

originating within the developing organism, e.g. genes

Question 19

What is an example of intrinsic factors?

Answer 19

Down syndrome
extra chromosome 21 (trisomy 21)
physical properties (e.g. facial features)
developmental delays and intellectual disability
behavioral dysfunction varies
abnormal dendritic spines in the cerebral cortex

Question 20

What are extrinsic factors?

Answer 20

outside the developing organism, e.g. exposure to alcohol before birth; environment

Question 21

what is an example of extrinsic factors - eg. changes in visual cortex depending on experience?

Answer 21

Binocular/monocular deprivation experiments
Sensitive period during which visual experience crucial for proper development of vision
Cats
1st 4 months – synaptic development in visual cortex
humans
- cataracts - blurry vision until 6 months (then corrected)
- impaired face perception at 9 years
- ‘lazy eye’ (amblyopia)
- impaired depth perception, unless corrected in childhood

Question 22

what is an example of extrinsic factors - eg. enriched environments: rats?

Answer 22

simple lab cages vs complex environment
Increased dendritic branching with complex environment
ALSO
- More hippocampal neurons
- Thicker cerebral cortex

Question 23

how do extrinsic factors eg. socio-economic status and brain development in humans affect brain development?

Answer 23

Family income is positively related to cortical surface area, particularly in:
Temporal, frontal and prefrontal regions
Relationships most prominent in regions supporting language, reading, executive functions and spatial skills
lower income: small differences in income associated with relatively large differences in surface area

Question 24

what is an example of extrinsic factors - eg. injury and recovery?

Answer 24

Timing of the injury is key

• Rats:
  
  • at birth - sparser dendrites in adults
  • At 10 days - expanded dendrites as adults
• Humans:
  
  • in the womb or soon after birth - most dramatic consequences
  • first two years —> may produce no behavioral consequences (e.g. language)
  • Adulthood —> severe behavioral consequences (e.g., language)
• Brain has capacity to compensate for injury & recover functions, depending on timing

Question 25

what is an example of extrinsic factors - eg. fetal alcohol syndrome?

Answer 25

prenatal exposure to alcohol
distinct facial features
changes in neuroanatomy
most common non-genetic cause of learning difficulties
severity varies:
- binge-drinking particularly harmful
- first trimester

Question 26

what is an example of extrinsic factors - eg. Zika virus?

Answer 26

transmitted through mosquito bites
mild symptoms - fever, rash, headache etc
Infection during pregnancy = microencephaly
- Abnormal brain development and loss of brain tissue

Question 27

how do intrinsic and extrinsic factors interact?

Answer 27

extrinsic factors can influence the expression of specific genes: epigenetic influences
- E.g., genetically identical mouse embryos implanted into 2 different foster mothers, behaviour is affected – effects of prenatal environments and postnatal experiences on how genes are expressed

Question 28

How are age demographics changing?

Answer 28

• 1900: 4% 65+
• 2030: 20% 65+

Question 29

Who do dementias affect?

Answer 29

• 1-6% over 65s
• 10-20% over 80s
  Projections over the next 35 years estimate that 10-20 million elderly people in the United States will have mild to severe cognitive impairments

Question 30

what are 3 examples of typical changes as we age?

Answer 30

Age-related decline in:
perception
motor function
memory and executive function

Question 31

why do typical changes occur as we age?

Answer 31

myelin loss
reduction in size of specific brain areas (e.g. hippocampus)

Question 32

what are atypical changes as we age (disorders)?

Answer 32

Dementia: acquired & persistent intellectual impairment
- Memory & cognitive deficits
- Impairment in social & occupational functioning

two types of dementias:
1. non-degenerative
- Mostly caused by problems in cardiovascular system (eg. vascular dementia)
2. Degenerative
- Primary cause in nervous system (eg. Alzheimers, Parkinsons)
- Thought to have a degree of genetic transmission

Question 33

what is Alzheimers disease?

Answer 33

65% of all dementias
begins as a loss of memory for recent events
progresses to being unable to answer basic Qs
atrophy of the cerebral cortex, particularly temporal and frontal areas
cellular changes in the hippocampus which impair synaptic function:
- increase of senile/amyloid plaques (protein (beta-amyloid) from dead neurons)
- increase in neurofibrillary tangles (protein Tau) – abnormal filaments in nerve cells

Question 34

what is a genetic risk factor of alzheimers?

Answer 34

Apoe4 gene

Question 35

what are some examples of protective factors of Alzheimers?

Answer 35

physical and mental activity; adequate sleep; higher education; bilingualism(?)

Question 36

what is Parkinson’s disease and what are some key symptoms in motor behaviour?

Answer 36

loss of cells in substantia nigra (basal ganglia), and consequent loss of the neurotransmitter dopamine

key symptoms in motor behavior:

• tremor at rest
• loss of spontaneous movement
• rigidity
• posture disturbances
• cognitive slowing

Question 37

What is an environmental risk factor of Parkinson’s?

Answer 37

environmental pollutants

Question 38

How is Parkinson’s treated?

Answer 38

physical therapy; L-dopa (dopamine precursor); deep brain stimulation

Question 39

What is neuroplasticity?

Answer 39

The potential of the nervous system to change across the life-span as an adaptation to the environment

Question 40

Explain neuroplasticity in romanian orphans

Answer 40

• Barren environments; lack of caregiver interaction
  Malnourished; cognitive development impaired
  Smaller brains; reduced brain activityBUT, foster care —> rapid developmental gains, IF adopted early
  Brain can recover from brief (< 6 months) extreme deprivation