Brain Development

Question 1

Describe the development of the nervous system from early embryonic stages through adulthood.

Answer 1

The nervous system develops in an intricately coordinated process from early embryonic stages all the way through childhood, adolescence, and adulthood. During early development, the brain forms the ability to dynamically transfer information across billions of interconnected neurons. This enables the coordination and control of mental and bodily functions, including perception, cognition, and movement.

Question 2

Embryonic stage

Answer 2

The embryo is initially formed through fertilization, which occurs when a sperm cell and an egg cell unite into a single cell. This fertilized egg cell, or zygote, starts dividing through the process of mitosis to generate the cells that make up an entire organism.

Question 3

The three layers

Answer 3

Sixteen days after fertilization, embryonic cells form three layers that develop into different body tissues.
* endoderm
* mesoderm
* ectoderm

Question 4

Endoderm

Answer 4

The endoderm, or inner tissue, is responsible for generating the lining tissues of various spaces within the body, such as the mucosae of the digestive and respiratory systems.

Question 5

Mesoderm

Answer 5

The mesoderm, or middle tissue, gives rise to most of the muscle and connective tissues.

Question 6

Ectoderm

Answer 6

The ectoderm, or outer tissue, develops into the body’s outer layer of skin, hair, nails, as well as the nervous system. It is probably easy to see that the outer tissue of the embryo becomes the outer covering of the body.

Question 7

When does the human nervous system begin to form?

Answer 7

Two weeks into embryonic development, the human nervous system begins to form. As the embryo develops, a portion of the ectoderm differentiates into the precursor for the tissue of the nervous system.

Question 8

What is the neural plate and how does it contribute to nervous system development?

Answer 8

Cells that differentiate from the ectoderm form a neural plate, which folds inward to create a neural groove lined by neural folds. These folds fuse to form the neural tube, setting the foundation for the brain and spinal cord.

Question 9

What is the neural crest and how does it contribute to the development of the nervous system?

Answer 9

Cells from the neural folds eventually separate from the ectoderm to form a cluster of cells referred to as the neural crest, which runs lateral to the neural tube. Neural crest cells migrate away and develop into several parts of the peripheral nervous system (PNS), including the enteric nervous system that governs the function of the gastrointestinal tract.

Question 10

Where does the CNS develop?

Answer 10

The Central Nervous System develops along the neural groove.

Question 11

What happens during the third week of embryonic development?

Answer 11

During the third week, the anterior end of the neural tube develops into the brain, and the posterior portion forms the spinal cord. This basic arrangement leads to more complex nervous system structures by the fourth week.

Question 12

What are the three primary vesicles of the developing brain?

Answer 12

• the forebrain (prosencephalon)
• the midbrain (mesencephalon)
• the hindbrain (rhombencephalon)
• they are generated by the anterior end of the neural tube which begins developing into the brain

Question 13

Where is each primary vesicle located in the neural tube?

Answer 13

Forebrain is uppermost, midbrain is next, and hindbrain is lowest.

Question 14

When do the primary vesicles differentiate into secondary vesicles?

Answer 14

Primary vesicles begin to differentiate into five secondary ones by the 5th week of embryonic development.

Question 15

Secondary vesicles

Answer 15

• telencephalon
• diencephalon
• mesencephalon (midbrain)
• metencephalon
• myelencephalon

Question 16

How does the forebrain (prosencephalon) differentiate?

Answer 16

It divides into the
* telencephalon -> becomes cerebrum: cerebral cortex, hippocampus, basal ganglia
* diencephalon -> thalamus + hypothalamus

Question 17

Thalamus and hypothalamus roles

Answer 17

Thalamus= the central relay hub for sensory signals Hypothalamus = involved in homeostasis and regulating functions including hunger, sleep, and mood

Question 18

What happens with the midbrain?

Answer 18

It remains as the mesencephalon, composed of the tectum, cerebral aqueduct, tegmentum, and cerebral peduncles. It is involved in head/eye movements, motivation, and reward.

Question 19

How does the hindbrain (rhombencephalon) differentiate?

Answer 19

It divides into the metencephalon (forms pons and cerebellum) and myelencephalon (forms medulla oblongata - breathing, digestion, heart rate, blood pressure).
* cerebellum = 10% of brain’s mass; coordinates movement, posture, and cognition
* The cerebellum connects to the rest of the brain via the pons, because the pons and cerebellum develop out of the same vesicle.

Question 20

Brain stem

Answer 20

Is composed of the structures formed by the midbrain and the hindbrain, with the exception of the cerrebellum -> midbrain, pons, medula oblongata

Question 21

What are the two main types of cells in the brain?

Answer 21

Neurons and glial cells (neuroglia).

Question 22

What are neurons, and what is their primary function?

Answer 22

Neurons are electrically excitable cells that transmit signals (action potentials) to other neurons. They are the fundamental units of the brain and nervous system and are responsible for communication, sensation, movement, and information processing.

Question 23

What are glial cells, and what is their main role?

Answer 23

Glial cells, or neuroglia, are support cells that help neurons function and communicate. They do not transmit electrical signals but provide essential support for the nervous system

Question 24

How many main types of glial cells are there, and where are they found?

Answer 24

There are six main types of glial cells: four in the central nervous system (CNS) and two in the peripheral nervous system (PNS).

Question 25

CNS Glial Cells

Answer 25

* Astrocyte - support * Oligodendrocyte - insulation, myelination * Microglia - maintenance of neural networks * Ependymal cell - creating cerebrospinal fluid

Question 26

PNS

Answer 26

* Satellite cell - support * Schwann cell - insulation, myelination

Question 27

What is the first stage of neuron growth after the neural tube closes?

Answer 27

The first stage of neuron growth begins after the neural tube has closed. This is called neural proliferation, and begins in the ventricular zone of the neural tube.

Question 28

When does neurogenesis (new neuron generation) begin in embryonic development?

Answer 28

Neurogenesis begins about four weeks after conception. Neurogenesis = the process of generating new neurons

Question 29

When does most neurogenesis in the human telencephalon occur?

Answer 29

Most neurons in the telencephalon (cortex, hippocampus, basal ganglia) are generated before birth. After birth, neurogenesis extensively occurs in the cerrebellum. * the bulk of neurogenesis (i.e., the 86 billion neurons) in the CNS occurs between the fourth week post-conception to 18 months after birth—during this early developmental period, approximately 4.6 million neurons are generated every hour

Question 30

What are the cells formed during neural proliferation?

Answer 30

Neural stem cells are formed during neural proliferation.

Question 31

What are the two basic types of stem cells, and how do they differ?

Answer 31

Pluripotent cells can become any cell type in the body, while multipotent cells can form the embryo and extraembryonic tissues (though often "multipotent" is compared as being more limited than pluripotent)

Question 32

What is the significance of pluripotent stem cells in medicine?

Answer 32

Pluripotent stem cells are being studied for regenerative treatments (e.g., diabetes, spinal cord injuries, heart disease) because they can develop into any cell type.

Question 33

What do neural stem cells produce during CNS development?

Answer 33

Neural stem cells are special cells which produce radial glial cells, which then differentiate into neurons and glial cells

Question 34

What is the ultimate result of neural proliferation?

Answer 34

Neural proliferation generates billions of cells that develop into the complex structure of the central nervous system (CNS).

Question 35

What can newly formed neurons do after they are generated?

Answer 35

They may stay and continue dividing or migrate to other parts of the nervous system.

Question 36

What is neuronal migration?

Answer 36

It is the process by which neurons move from their original location to a new target location in the nervous system.

Question 37

Where does migration occur for central nervous system (CNS) neurons?

Answer 37

Migration remains within the neural tube for CNS neurons.

Question 38

Where does migration occur for peripheral nervous system (PNS) neurons?

Answer 38

Migration for PNS neurons may occur across different neural regions.

Question 39

What are immature neurons like during migration?

Answer 39

They lack fundamental neuronal characteristics such as axons and dendrites.

Question 40

What supports neuronal migration?

Answer 40

Sophisticated molecular and cellular signaling that pulls and pushes immature neurons to their targets.

Question 41

Describe the general pattern of neuronal migration.

Answer 41

Migration typically follows an inside-out pattern: neurons travel from the inside of the neural tube outward to their target.

Question 42

What are the two main modes of neuronal migration?

Answer 42

Radial migration = Neurons are guided by radial glial cells to move toward the brain surface, establishing the layered structure of the neocortex (primary mode). Tangential migration = Neurons move orthogonally to the direction of radial migration, sometimes to the surface of the CNS. * these are not mutually exclusive, neurons may alternate between these modes during their migration.

Question 43

What are the two main mechanisms of neuronal migration?

Answer 43

Somal translocation = An extension from the neuron’s soma leads it to its target, used in both radial and tangential migration. Glial-mediated migration=Immature neurons "climb" along extended glial cells to reach their target locations; specific to radial migration.

Question 44

What happens after neurons reach their target locations?

Answer 44

They develop dendrites and axons, enabling communication and the formation of functional neural circuits.

Question 45

What is aggregation in the context of neuronal development?

Answer 45

Aggregation is the process by which migrating neurons align and integrate with other neurons to form neural circuits.

Question 46

What are the two key mechanisms that support neuronal aggregation?

Answer 46

Cell-adhesion molecules on cell surfaces recognize and bind to molecules on other cells, enabling cell-to-cell interactions and tissue stabilization. Gap junctions form communication channels between adjacent cells, allowing exchange of ions and metabolites like glucose.

Question 47

What do cell-adhesion molecules do?

Answer 47

They recognize and bind to molecules on other cells, enabling cell-to-cell interactions and helping to stabilize tissue.

Question 48

What are gap junctions, and what is their function in neuronal aggregation?

Answer 48

Gap junctions are communication channels between adjacent cells that allow the exchange of ions and metabolites such as glucose, promoting biochemical coupling.

Question 49

What is the result of neuronal aggregation and integration?

Answer 49

These processes facilitate neuronal interactions and integration, ultimately forming the neural circuitry of the human nervous system.

Question 50

What is neuronal cell death, and why is it important during development?

Answer 50

Neuronal cell death is the elimination of neurons in the nervous system. It occurs extensively during development and actually supports healthy brain development by refining neural networks.

Question 51

What are the two main types of neuronal cell death?

Answer 51

Apoptosis (programmed, controlled cell death) and necrosis (passive, accidental cell death).

Question 52

What is apoptosis?

Answer 52

Apoptosis is active, programmed cell death that selectively eliminates excess and immature neurons, supporting proper neuronal connectivity and network maturation.

Question 53

What is necrosis?

Answer 53

Necrosis is passive, accidental cell death resulting from trauma, toxins, or oxygen depletion. It is characterized by cell swelling, membrane rupture, and leakage of cellular contents. It can result from a stroke, where disrupted blood flow leads to accidental cell death, or TBI. Excessive necrosis is associated with pathologies such as Alzheimer's Disease and Parkinson's disease.

Question 54

How do apoptosis and necrosis differ in their effects on surrounding tissue?

Answer 54

Apoptosis efficiently dismantles and removes dead neurons, minimizing disruption. Necrosis leaves behind cellular debris, which can disrupt surrounding brain tissue.

Question 55

Why is understanding and regulating cell death important?

Answer 55

Understanding and regulating cell death is crucial for preserving brain function and preventing neurological diseases.

Question 56

What was the traditional view about new neuron generation in the adult human brain?

Answer 56

Until about 25 years ago, it was believed that new neurons could not be generated after birth, although it remains a controversial topic.

Question 57

Where is adult neurogenesis most consistently observed in the brain?

Answer 57

* Subventricular zone of the lateral ventricles * Subgranular zone in the dentate gyrus of the hippocampus * Such neurons often do not survive or integrate into existing neural circuits.

Question 58

What is neuroplasticity?

Answer 58

Neuroplasticity is the brain’s ability to reorganize or “rewire” its connections in response to experience.

Question 59

How does learning relate to brain structure?

Answer 59

Learning something new physically changes the structure of your brain through neuroplasticity.

Question 60

How does the brain store information?

Answer 60

The brain stores information in networks of modified synapses, and activating these networks allows retrieval of the information

Question 61

What is Hebb’s rule?

Answer 61

“Neurons that fire together, wire together.” If two neurons are active at the same time, the synapses between them are strengthened.

Question 62

What is long-term potentiation (LTP)?

Answer 62

LTP is a persistent strengthening of a synaptic connection based on simultaneous activation of neurons.

Question 63

What role do NMDA receptors play in LTP?

Answer 63

NMDA receptors, normally blocked by magnesium, open when rapid presynaptic inputs depolarize the postsynaptic neuron, allowing calcium to enter and trigger AMPA receptor insertion.

Question 64

What happens to AMPA receptors during LTP?

Answer 64

AMPA receptors migrate from inside the postsynaptic cell to the membrane, making the neuron more responsive to glutamate and strengthening the synapse.

Question 65

What is long-term depression (LTD)?

Answer 65

LTD is the weakening of synaptic connections, often by removing AMPA receptors from the membrane, making the neuron less

Question 66

Why is LTD important for learning and memory?

Answer 66

LTD weakens and prunes unused synapses, allowing important connections to stand out and making learning more efficient.

Question 67

How do drugs of abuse relate to LTP?

Answer 67

Some drugs of abuse co-opt the LTP pathway, leading to synaptic strengthening that can contribute to addiction.

Question 68

Is neuroplasticity only about strengthening synapses?

Answer 68

No, neuroplasticity also involves weakening some synapses (via LTD) to refine neural circuits.

Question 69

Is synaptic strengthening specific?

Answer 69

Yes, LTP is specific to neurons activated simultaneously, strengthening only those connections.

Question 70

Sensitive periods

Answer 70

Sensitive periods refer to developmental time windows during which experiences have an especially strong impact on brain organization. While similar experiences can still affect the brain outside of these sensitive periods, the consequences for brain reorganization will not be as strong. Involves heightened neuroplasticity

Question 71

Critical periods

Answer 71

Critical periods refer to the limited time windows during which experiences, or lack thereof, have lasting effects on brain function and behavior. Disruptions during critical periods due to atypical experiences or adversity may lead to irreversible changes to brain structure. Involves heightened neuroplasticity.

Question 72

How do sensitive and critical periods differ?

Answer 72

Sensitive periods offer broad windows for experience to shape neural circuitry, while critical periods are a subset that can result in irreversible changes to the brain.

Question 73

Example sensitive period

Answer 73

Language acquisition (especially second language learning) is a sensitive period—peak proficiency is more likely when exposure occurs in early childhood. A study found that childrenm(Chinese+ Korean) who began learning the second language (English) before age 7 were able to reach proficiency akin to native English speakers; children arriving between age 7 and puberty were less proficient; and after puberty, an individual’s second language proficiency is likely to remain low. These findings support a brain-maturation account, such that the ability to learn languages gradually declines and ultimately flattens as the brain matures. This is not to say learning a second language is impossible after puberty, it just becomes harder, because Lower neuroplasticity after the sensitive period contributes to slower and less successful second language learning.

Question 74

Example critical period

Answer 74

Can be exemplified in sensory development and first-language learning. Depriving an animal of visual input during infancy leads to irreversible vision impairment because the brain reorganizes to prioritize input from the non-deprived eye.

Question 75

What is cross-modal plasticity?

Answer 75

Cross-modal plasticity is the brain’s ability to reorganize so that regions normally used for one sense (e.g., vision) process input from other senses (e.g., touch or hearing) after sensory l

Question 77

How does cross-modal plasticity affect individuals with early blindness?

Answer 77

Their occipital cortex (usually for vision) shifts to process tactile and auditory sensations, and this reorganization can persist even if vision is restored.

Question 78

Language as a critical period

Answer 78

In the early 1970s, the tragic story of Genie, an adolescent girl who for most of her childhood experienced severe isolation and neglect, caught the world by storm. When discovered, Genie was unable to communicate verbally with language. Researchers studied Genie’s linguistic development over many years and concluded that, despite initial progress in speech and grammar, her language proficiency remained severely impaired

Question 79

What is adolescence considered in terms of brain development?

Answer 79

Adolescence (ages 10–24) is widely considered a sensitive period for brain development due to significant social, cognitive, and emotional changes.

Question 80

Adolescent Brain

Answer 80

Substantial neuroimaging research has shown that the frontal lobes, which include regions of the brain involved in executive function, such as the prefrontal cortex, are late-developing and undergo significant maturation that continues well into adolescence. Subcortical regions, on the other hand, develop much earlier, around early adolescence. Parallel to these brain development findings, prior work indicates that adolescence is marked by increased sensation-seeking and risk-taking behaviors

Question 81

Can risk-taking in adolescence be positive?

Answer 81

Yes, some risk-taking is essential for identity formation, decision-making skill development, and fostering independence.

Question 82

Neural efficientcy and neuroplasticity

Answer 82

high neuroplasticity and flexibility in a brain network corresponds to low stability and efficiency, and vice versa.

Question 83

How is brain development influenced by external factors prenatally

Answer 83

Prenatal brain development is highly sensitive to external (environmental) factors, especially because the brain is forming its basic structure and circuitry during this time. * maternal nutrition * maternal stress * substance exposure -> alcohol, nicotine, drugs * infections and viruses * hormonal imbalances * ocygen supply * medication use * social factors (DV, poverty)

Question 84

How is brain development influenced by external factors postnatally

Answer 84

* nutrition * appropriate stimulation * secure caregiver attachment * environment (clean/dirty) * exposure to stress/trauma * sleep quality * screen time and social media use * illness

Question 85

What brain regions are responsible for drive and priority and how do they vary between adolescents and adulthood?

Answer 85

Prefrontal Cortex (PFC) * Function: Planning, decision-making, prioritization, impulse control. * Subregions: *Dorsolateral PFC: Goal-setting, working memory, abstract reasoning. Ventromedial PFC: Valuation and emotional decision-making. Orbitofrontal cortex: Evaluating rewards and consequences. 📌 Develops Last: The PFC is not fully mature until the mid-20s, making adolescents more prone to impulsivity and short-term thinking.