Lecture 8

Question 1

Neurobiology of development (2)

Answer 1

• Phylogenetic development
• Ontogenetic development
• B&B focuses on ontogenetic

Question 2

Phylogenetic development

Answer 2

Evolutionary development of species from lower to higher species

Question 3

Ontogenetic development

Answer 3

Development of an individual from the time of fertilisation to the organism’s mature form

Question 4

Vertebrates

Answer 4

Animals characterised by brain and spinal cord

Question 5

Embryos

Answer 5

Embryos of different species more closely resemble one another than their respective parents.
Embryos are not simply miniature versions of adults.

Question 6

Gross development of the human nervous system (4 steps)

Answer 6

• Zygote: conception of 2 weeks
• Embryo: 2-8 weeks
• Foetus: 9 weeks to birth
• Baby: birth

Question 7

Origin of brain cells (4)

Answer 7

• Neural stem cells
• Progenitor/precursor cells
• Neuroblasts or glioblasts
• Specialised cells
• NB: neural stem cells are multipotent - they give rise to the many specialised cell types in CNS

Question 8

How does a stem cell know what to become?

Answer 8

Development of brain cells is influenced by chemical signals.

Gene expression is influenced by:

• Neurotrophic factors (chemicals), which may express specific genes and signal a cell to develop in a particular way
• Gene methylation, which may suppress specific genes

NB: environmental influences may alter gene expression

Question 9

Stages of brain development

Answer 9

1. Cell birth (neurogenesis)
2. Cell migration
3. Cell differentiation
4. Cell maturation (dendrite and axon growth)
5. Synaptogenesis (formation of synapses)
6. Cell death and synaptic pruning
7. Myelogenesis (formation of myelin)

Question 10

Neurogenesis

Answer 10

Formation of neurons from stem sells in the neural tube is complete ~25 weeks after conception.

• Except in hippocampus
• NB: brain tumours in adults arise from glial cells (glioblastoma), brain tumours in children may also be neuronal (neuroblastoma)

Question 11

Neural migration

Answer 11

Migration: 8-29 weeks

Question 12

How do cells know where to go? - Neural migration

Answer 12

Radial glial cells pathways
Paths run from subventricular zone to cortical surface
Cortical layers develop from the inside out: first layer VI, then V.

• NB: some neurons go off road and follow chemical signals.

Question 13

Cell differentiation

Answer 13

Brain relies on a general purpose neuron that matures into a specific cell type in a specific location when exposed to local environmental chemicals.

• Essentially complete at birth

Question 14

Neural maturation

Answer 14

Dendrite development

• Dendritic arborisation begins prenatally and continues up to 2 years after birth.

Axon development

• Neurotropic chemicals attract or repel approaching growth cones

Question 15

Synaptogenesis

Answer 15

Human brain has 100 trillion synapses

• Simple synaptic contacts 5 months after conception.
• Extensive synaptic development in deepest cortical layers 7 months after conception.

NB: not all synapses in e.g., visual cortex are visually related (synesthesia)

Question 16

Cell death

Answer 16

Apoptosis = programmed cell death

• Superfluous neurons die through apoptosis because they depend on neurotrophic factors produced by target cells

Question 17

Synaptic pruning

Answer 17

Synapses on remaining neurons persist into adulthood only when incorporated into a specific functional network, other synapses are eliminated

• NB: synaptic pruning induced by environmental cues may lead to variation in neural connectivity and perception.

Question 18

Myelogenesis

Answer 18

Cerebral myelination is a rough index of cerebral maturation.
Increased connectivity in the default network is related to higher intelligence.

• Myelination of the cerebral cortex continues into adulthood
• White matter increases
• Grey matter decreases (NB: grey matter in language regions increases.

Question 19

Piaget’s stages of cognitive development

Answer 19

• Stage I: sensorimotor
• Stage II: preoperational
• Stage III: concrete operational
• Stage IV: formal operational

Question 20

Stage I: Sensorimotor

Answer 20

• Birth to 18-24 months
• Experience the world through senses and actions (looking, touching, mouthing)
• Object permanence, stranger anxiety

Question 21

Stage II: preoperational

Answer 21

• 2-6 years
• Represents things with words and images but lacks logical reasoning
• Egocentricism, language development

Question 22

Stage III: concrete operational

Answer 22

• 7-11 years
• Thinks logically about concrete events; grasps concrete analogies and performs arithmetical operations
• Conservation, mathematical transformation

Question 23

Stage IV: formal operational

Answer 23

• 12+ years
• Reasons abstractly
• Potential for mature moral reasoning

Question 24

Brain hormones

Answer 24

NB: behavioural differences between males and females are not solely the result of environmental experiences

• Androgens
• Estrogens

Induce changes in the brain

• Number of neurons
• Branching of dendrites
• Growth of synapses

Question 25

Androgens

Answer 25

Mainly testosterone

• Male sex characteristics
• Secondary sex characteristics
• Changes in the brain

Question 26

Estrogens

Answer 26

Estrone, estradiol, estriol

• Menstruation cycle, pregnancy

Question 27

Chemoaffinity hypothesis

Answer 27

Specific molecules in different cells in various midbrain regions give each cell a distinctive chemical identity.
Incoming axons seek out a specific chemical and long in a general midbrain region

NB: precise positioning of neural placement is induced by postnatal experience.