Lecture+7-Brain+Development

Exploration of the processes that lead to the formation and maturation of the brain.

Focus on:
- Formation of brain cells.
- Specialization of cells.
- Migration to designated areas.
- Connectivity among neurons.

Emergence of the human mind is a significant phenomenon.
Understanding initial brain construction aids in grasping how the brain adapts and reorganizes with influences and learning throughout life.
Diseases like schizophrenia and autism are increasingly viewed from a developmental perspective rather than solely adult conditions.

Embryonic Development Process:
- Starts with fertilization of the egg when the sperm unites with the egg.
- The fertilized egg is termed a zygote.

Initial Formation:
- Zygote undergoes cleavage (dividing processes) leading to a multi-celled structure.
- Transition from zygote to 8-cell stage and formation of blastula.
Gastrulation (Days 13-19):
- Three layers emerge:
  - Ectoderm: will develop into the nervous system and skin.
  - Mesoderm: will become muscles, bones, and blood.
  - Endoderm: will form internal organs.
Early Neural Development:
- Neural plate begins to form at around 2 weeks, folding to develop:
  - Neural Crest (Neural Folds)
  - Neural Groove
- Neural folds converge to create the neural tube by the end of the 3rd to 4th week, becoming the brain and spinal cord.
Primary Vesicles Formation:
- By week 8:
  - Prosencephalon: develops into the cerebrum.
  - Mesencephalon: becomes the midbrain.
  - Rhombencephalon: will evolve into the brainstem and cerebellum.
Brain Development at Birth:
- At birth, the brain structurally resembles a fully developed brain but continues to undergo significant growth in functionality and connections after birth.

Process of Development:
- Proliferation (Neurogenesis): Birth of new neurons primarily before birth.
- Cell Migration: Neuron travel to their final positions.
- Differentiation: Neurons develop specific characteristics and functions.
- Synaptogenesis: Formation of synapses.
- Cell Death (Apoptosis): Programmed cell death to maintain efficient neural networks.
- Synaptic Remodeling: Continual refinement of synapses based on activity.

Initially thought that adult brains could not produce new neurons; however, evidence suggests ongoing neurogenesis mostly in the hippocampus, impacting memory formation.
Exercise positively influences neurogenesis in the hippocampus.

Neurons travel from their birth region to their appropriate locations with the help of radial glial cells guiding their path.

Neurons differentiate by expressing specific genes upon reaching their destination.
Signals from neighboring cells influence differentiation outcomes.

Developing neurons create growth cones seeking out target cells.
Target cells release chemicals guiding the growth cones through attraction or repulsion.

Apoptosis occurs as a natural step, with a high percentage (20-80%) of neurons dying after competition for synaptic connections.
Neurotrophic factors from target cells support neuron survival, influencing growth and overall health of the neural network.

Importance of synaptic pruning, which begins around age two, optimizing neural connections and enhancing the efficiency of the brain's neural network throughout development.
There’s a significant synaptic loss from late childhood to mid-adolescence, particularly in the prefrontal cortex which is the last area affected.

The newborn brain, weighing approximately 370 grams, continues robust growth post-birth.
Rapid growth rate of 1% daily immediately after birth, tapering off to 0.4% by three months, eventually achieving about 90% of its adult size by age five.
An infant's brain contains 50% more synapses than an adult brain, necessitating pruning to maintain efficient operations.
Synaptic pruning optimizes the connectivity between neurons, promoting stronger connections and eliminating weaker ones.