Neural development Flashcards
How does the brain emerge?
Fertilization of egg → multicellular blastula
Ectodermal cells (blastula) →neural plate → neural groove → neural tube
Neural tube: Proencephalon →forebrain
Mesencephalon → midbrain
Rhombencephalon→ hindbrain
Caudal neural tube →spinal cord
What is neurulation?
the early process that go into forming the nervous system
Ectodermal cells on the dorsal surface form neural plate
As the nervous system continues to develop, the cells at the lateral borders of the neural plate push upward. → form neural groove
As the groove deepens, the cells pushing up at the border of the neural fold region eventually meet and fuse → form neural tube that runs anteriorly and posteriorly along the embryo.
At both ends of the neural tube are openings (neuropores), that close on, when the anterior neuropore is sealed, this cavity forms the primitive brain, consisting of 3 spaces, or ventricles.
From this stage on, the brain´s gross features are formed by the growth and flexion (bending) of the neural tube´s anterior portions.
Which signal is important in the signaling pathways defining neural development?
Wnt signaling controls the initial formation of the neural plate and many subsequent patterning decisions in the embryonic nervous system, including the formation of the neural crest.
What is a hox gene?
One group of animal genes containing homeobox sequences is specifically referred to as Hox genes.
is responsible for determining the general body plan, such as the number of body segments of an animal, the number and placement of appendages, and animal head-tail directionality.
The majority of Hox genes are expressed in the CNS, where they have critical functions in the neuronal specification and target connectivity.
Where are new neuron and glia cells created?
During prenatal development, closer to the hollow of the neural tube are several proliferative zones in which neurons and glial cells are produced by the division of proliferating cells. They are
Neuroblasts = stem cells for neuron
Glioblasts = stem cells for glia, differentiate into astrocytes and oligodendrocytes.
What accounts for postnatal development?
Growth of synapses = synaptogenesis Growth of dendrites Growth of axon bundles The proliferation of glial cells Myelination of nerve fibers
What is neuronal proliferation?
Neuronal proliferation is the process of cell division in the developing embryo and fetus. It is responsible for populating the nervous system with neurons.
What is the developmental pruning of synapses?
Synaptic pruning is a natural process that occurs in the brain between early childhood and adulthood, the brain eliminates extra synapses.
How does pruning happen?
- Infancy: large amount of brain growth, explosion of synapses formation between neurons → vital role in learning, memory formation, and adaptation early in life
- At about 2-3 years of age, the number of synapses hits a peak level → remove synapses that it no longer needs. → pruning
Once the brain forms a synapse, it can either be strengthened or weakened. This depends on how often the synapse is used. In other words, the process follows the “use it or lose it” principle: Synapses that are more active are strengthened, and synapses that are less active are weakened and ultimately pruned.
What influences synaptic pruning?
- Early synaptic pruning is mostly influenced by our genes.
- Later on, it’s based on our experiences.
What is pruning in a deep neural network?
removing unimportant weights from a network –> pruning synapses
removing nodes –> pruning neurons
What are the benefits of pruning and its effect?
Better generalization
Fewer training examples required
Improved speed of learning and/or classification
Pruning synapses → making the network sparse
Pruning neurons → making network dense
How does cortical development happen?
- Precursor cells are undifferentiated cells from which all cortical cells arise through cell division and differentiation.
- First 5-6 weeks of gestation, cells in the subventricular zone divide in a symmetrical fashion → exponential growth in numbers of precursor cells.
- At the End of 6 weeks, precursor cells → asymmetrical division begins → one of the two cells after division becomes a migratory cell destined to be a part of another layer, the other cell remains in the subventricular zone
- Migratory cells travel outward to the surface of the developing cortex →cortical plate → cortex is built inside out: the first neurons to migrate lie in the deepest cortical layers, whereas the last to migrate move farthest toward the cortical surface.
Where does neurodevelopment happen during our lifetime? esp. after birth
Neurogenesis in adult mammals has now been well established in 2 brain regions
Hippocampus → key role in learning and memory
Olfactory bulb
What is a deep belief network? and how can it be used?
Deep Belief networks (DBN) are layer-based networks that are collections of simple, unsupervised networks such as restricted Boltzmann machines.
- Firstly, when trained on a set of examples without supervision, a DBN can learn to probabilistically reconstruct its inputs.
- Then, a DBN can be further trained with supervision to perform classification.
