Brain Development Week 1 Flashcards
In what gestational week does human brain development begin?
Week 3
When does neuron production in humans begin?
Embryonic day 42 (42 days post conception)
This process is largely complete by mid-gestation.
Fill the blanks:
The brain increases in size by —- fold during the preschool period, reaching approximately ——% of adult volume by age 6.
4 fold
90%
How does the connectivity of the brain in the early postnatal period compare to that of adults?
During the early postnatal period, the connectivity throughout the developing brain far exceeds that of adults. Connectivity is gradually pruned back via competitive processes that are influenced by experience.
How many neurons (in general) does the mature human brain contain?
More than 100 billion
Label the parts of this neuron
1 Dendrites (collections of dendrites knows as dendritic arbors)
2 Nucleus
3 Cell body
4 Node of Ranvier
5 Schwann cell
6 Myelin sheath
7 Axon
8 Axon terminal
What is the point of connection between two neurons called?
A synapse
What does gray matter comprise of?
Neocortex and subcortical nuclei
What is the neocortex?
A 2-5mm thick layer of cells that lies on the surface of the brain. (Cortex comes from latin term meaning tree bark)
Image: Neocortex: The thin,dark purple strip that follows the brain surface.
Although it may appear to be uniform, it is parcellated into structurally and functionally distinct areas, giving rise to specialised brain areas.
What is the main function of dendrites?
To RECEIVE electrochemical input signals from other neurons.
What is the main function of axons?
Like telephone wires, they send electrochemical signals to neurons located in distant locations. §
What does white matter refer to?
Fibre pathways of the brain comprised of fiber tracts (bundles of axons). Axons are wrapped in myelin which is white in appearance.
List five facts about the ventricular system of the brain.
- Filled with CSF which is completely recycled several times a day.
- Cushions and protects brain.
- Removal of waste.
- Transport of hormones and other substances.
- **During brain development, the walls of the ventricles are the site of most neuron production. **
What is the first step in brain development?
Differentiation of the neural progenitor cells.
What is gastrulation?
A set of processes that begins of embryonic day 13 and transforms an embryo from a blastula (blastocyst in mammals consisting of an epiblast and hypoblast) to a three layered structure that sets the stage for all subsequent developments in the embryo.
What is the first step in the process of gastrulation?
The appearance of the primitive streak, a slit like opening in the upper layer of the embryo which provides access to the lower regions of the embryo.
FYI embryo turns to foetus in week 8.
The rostral end of the embryo will turn into what part of the baby?
Head
Name the three layers of the gastrula and what they develop into.
Endodermal layer: Gives rise to structures of the gut and respiratory tract.
Mesodermal layer: Muscle, bone, cartilage, vascular system.
Ectodermal layer: Epidermal ectodermal stem cells give rise to skin, nails and sweat glands. Neuroectodermal stem cells (neural progenitor cells) give rise to brain and CNS. The region of the embryo containing neural progenitor cells is called the NEURAL PLATE.
Why is gastrulation important?
- Forms the basis of the body plan including primary body axes.
- During gastrulation, movements bring cells into close proximity with each other allowing for inductive interactions that are the basis of neurulation and organogenesis.
What can happen when gastrulation goes wrong?
Severe congenital malformations
Conjoined twinning
Spina bifida
Disease in adulthood: cancer/immune system malfunction
What is the primitive node?
A molecular signalling center located at the rostral end of the primitive streak. Cells of the primitive node send signals to cells migrating along the midline of the embryo and these signals trigger gene expression in the migrating cells. This triggers the differentiation of epiblast cells into neural progenitor cells.
What role does the primitive node play?
Sends signals that trigger gene expression resulting in cell differentiation.
Sends signals that establish the rostral-caudal organisation of the embryonic nervous system.
When does the neural tube develop?
In the third week of gestation between E20 and E27.
Which morphogens play an essential role in the early patterning of the presumptive neocortex?
Emx2 and Pax6
Produced in opposite gradients along the anterior-posterior extent of the neocortical proliferative zone. Conce of Emx2 highest in posterior and medial regions.
Interaction of these two gradients contributes to early patterning of the neocortex.
When does neuron production begin in the embryonic period?
E42
Most of our billions of neurons are produced by mid-gestation.
Neurons are post-mitotic cells, once formed they are no longer capable of dividing and producing new cells.
When is cortical neurogenesis complete in humans?
E108
What are Cajal-Retzius cells? (CR cells)
Cells that control the positioning of neurons into the correct layers of cortex. They produce a molecular signal called reelin, that it part of the pathway that signals neurons when to stop migrating and take up their positions in the cortex.
What is fate restriction?
Describes the phenomenon whereby in early corticogenesis, progenitor cells can receive signals to produce any neural line but as development proceeds, the progenitor loses the capacity to generate those cells.
McConnell experiments transferring progenitor cells from younger donor animals to older ones and vice versa*
Axons———
Dendrites———-
(Receive input from other neurons/Send signals from the neuron)
Axons send
Dendrites receive
When does the formation of the thalamocortical and corticothalamic pathways begin and end?
TC pathway (body to brain) and CT pathway (brain to body) begin to form by the later part of the second trimester and are complete by GW 26.
