Week 11 - Brain Development and Plasticity

Question 1

How does a brain begin to form?

Answer 1

Neural plate forms at day 16, plate lengthens and folds into neural tube (NT) at 22 days, fully forms and begins to form brain and spinal cord at day 27.

Question 2

What are Neural Tube Defects (NTD)?

Answer 2

occurs if NT fails to close properly, leaves part of brain or spinal cord exposed which are then vulnerable to damage. Varying degrees of damage can be fatal.

Question 3

What happens in the three-vesicle stage?

Answer 3

Cranial part of NT enlarges and differentiates into the forebrain midbrain and hindbrain. Completed by week 3-4.

Question 4

What are the stages of neuronal development?

Answer 4

Proliferation (ie. neurogenesis/gliogenesis), Migration, Differentiation, Synaptogenesis, Myelogenesis(formation of myelin). Stages occur simultaneously.

Question 5

What happens in the proliferation period of neuronal development?

Answer 5

The brain grows and develops, at peak 250,000 neurons formed per minute, mostly complete by 5 months with exception of olfactory bulb and hippocampus cells.

Question 6

What happens in the migration period of neuronal development?

Answer 6

Neural progenitor cells migrate at different rates and directions, aim to reach target cell.

Question 7

What happens in the differentiation period of neuronal development?

Answer 7

The stage when a neural progenitor cell begins to take on the appearance & characteristics of a specific neuron
Involves: Formation of axon and dendrites, Acquisition of enzymes required to produce neurotransmitters, and Acquisition of receptors to receive synaptic transmissions

Question 8

What happens at the synaptogenesis period of neuronal development?

Answer 8

Formation of synapses, Lifelong but slows as age, 1-2yrs old = Peak synapse formation.

Question 9

What happens in the myelogenesis period of neuronal development?

Answer 9

Myelin surrounds the axon forming an electrically insulating sheath. Oligodendrocytes form myelin in CNS. Moves from the spinal cord to Hindbrain, Midbrain and Forebrain. Slow process ie. 10 to 12 years after birth.

Question 10

What is Apoptosis?

Answer 10

Programmed cell death. Removes unwanted neurons in a controlled manner. Maximal during late prenatal stage - reduces 28 billion neurons to 23 billion by birth.

Question 11

Overall, what happens in the embryonic stage (conception to week 8 gestation), (with regards to brain development)?

Answer 11

Rudimentary structures of the brain produced.
•Major compartments of central & peripheral nervous systems defined.
•Neuron production starts week 6 gestation.

Question 12

Overall, what happens in the Foetal Stage (week 9 gestation to birth), (with regards to brain development)?

Answer 12

• Characteristic pattern of gyral and sulci folding. •Development of the neocortex.
• Brain development focuses on neurogenesis, migration & differentiation.
• Neuronal cell loss.

Question 13

What are the characteristics of a newborn brain?

Answer 13

One ­quarter of its adult size.
Spinal cord and brain stem well developed.
Limbic system and cerebral cortex still primitive.

Question 14

What are the characteristics of brain development from birth to toddler age?

Answer 14

Synaptogenesis in cerebral cortex – ‘The exuberant period’
At its peak, the cerebral cortex creates 2,000,000 synapses/sec
Corresponds with mental milestones
Myelination most rapid in first 2 years
By two years old the brain is about 80% of its adult size

Question 15

What brain development occurs from toddler to adolescent age?

Answer 15

Over­abundant amount of synapses in all areas of the cerebral cortex exists throughout middle childhood.
Synaptic pruning increases.
Brain = 90% of adult volume by age 6.

Question 16

What three main methods of synaptic pruning are proposed?

Answer 16

Axon degeneration, Axon retraction, and Axon shedding. All result in axon removal and subsequent deletion of synapse. Hormones and neurotrophins likely to play a major role in process.

Question 17

What is the Hebb rule?

Answer 17

Neurons that wire together fire together.

Question 18

What brain development occurs during the adolescence period (13-18)?

Answer 18

Synaptic pruning continues until end of adolescence, therefore, grey matter decreases in volume. Myelination continues especially in the frontal cortex, therefore, white matter increases in volume.

Question 19

What is theorised to be one of the reasons for “teen impulsiveness”?

Answer 19

The prefrontal cortex matures later than limbic and reward systems, which leads to neural imbalance.

Question 20

How does the brain change from the end of adolescence to 60s?

Answer 20

Brain reaches its peak power at age 22 and lasts about 5 years, from there functions begins to slowly decrease. Cortex becomes thinner, myelin sheath begins to degrade, Decrease in brain plasticity, and Chemical changes lead to a decrease in memory, reasoning, spatial skills and speed of thought.

Question 21

For experimental purposes, what age is considered elderly?

Answer 21

65 onwards.

Question 22

What is dementia?

Answer 22

A set of symptoms that may include persistent disorder of the mental processes caused by brain disease or injury and marked by memory disorders, personality changes and impaired reasoning.

Question 23

Do our brains stop developing?

Answer 23

YES - if considering certain structural and functional aspects eg. Brain size, speed of neural processing.
NO- if considering Neuroplasticity.

Question 24

What is neuroplasticity?

Answer 24

The capacity of the nervous system to reorganize itself by forming new neural connections.

Question 25

What are some neuroplasticity mechanisms involved in learning and memory?

Answer 25

Strengthening of existing synapses, Formation of new synapses, Elimination of old synapses, and Modification of dendritic branches.

Question 26

What are some neuroplasticity changes involved in learning to read?

Answer 26

Individuals who learned to read as adults were compared to those who never learned to read and there was increased grey matter and corpus callosum in those who learned to read, meaning the brain likely changes as a result of learning.