Cortical Development Flashcards
(38 cards)
Stages of Brain Development
- 0-4 weeks: Neurolation
- 4-8 weeks: Neuronal Proliferation
- 12-Birth: Neural Migration
- 16/18 weeks – late childhood: Apotosis
- 18 weeks – Late childhood: Synaptogenesis
- 30 weeks – Adulthood: Myelination
Neuronal Proliferation
Neurons destined for the neocortex are produced in the proliferative zone near the cerebral ventricle (ventricular zone)
(proliferation means cells greatly increase in #)
organizer controls pattern of proliferation via chemical signals in neural tube
Neurolation
Folding & fusion of the ectoderm to create the neural tube
Neural tube becomes the CNS
Happens week 0-4;
Week 5: ecotoderm differentiated into different brain structures
Neural Migration
Neurons migrate along radial glial cells to the relevant layer of the cortex
phase 3 of prenatal development
cells need to migrate from ventricular zone and aggregate in this process
Brain volume growth
Total: Peak = 10 (females) & 14 (Males)
Grey: Peak = 10 (males) & 8 (females)
WM: steep increase in first year; Then less rapid growth up to young adulthood
Grey Matter in adolesence
So despite global changes in GM – we can see that it the thickness that is showing the most marked reduction
Change in grey matter volume refers to a change in:
Thickness
Surface area
Sulcation
Process of brain growth in the 2nd – 3rd trimester
Abnormality = Lissencephaly (smooth brain)
Abnormality of sulcation
Lissencephaly (smooth brain)
Gyrification
development of the surface folds
Sulcation development
13-17 gestational weeks - appearance of the first sulcus
18-19 gestational weeks - development of the periinsular sulci
20-22 gestational weeks - central sulci and opercularization of the insula
24-26 gestational weeks - covering of the posterior insula
27-28 gestational weeks - closure of the lateral sulcus (Sylvian fissure or lateral fissure)
3 types of sulci
Primary
Consistently located
Easily recognisable
Central and Superior Frontal
2) Secondary
Branches of the Primary Sulci
3) Tertiary
Branches of the secondary Sulci
Individual differences
8/9month of pregnancy and into first year of life
Theories of Gyrification
- Skull preventing the brain growing
- Axonal Tension Theory
- Differential Radial Growth – Richman 1975
- Differential Tangential Growth – Ronan 2014
- Constrained cortical expansion - Tallinen 2014, 2016
Axonal Tension Theory
Axons connecting two areas are pulling on cortex and this causes them to fold. BUT: Axonal tension does exist but it quite weak; there are more gyri than sulci
Constrained Cortical Expansion
Grey matter is expanding rapidly
White matter isn’t
Based on this theory:
Polymicrogyria based on Constrained Cortical Expansion Theory
Poly microgryia = thin cortex but large surface area so it folds more
Lissencephaly based on Constrained Cortical Expansion Theory
Lisencephaly = thick cortex but low surface area so it folds less
2 ways neurons migrate along radial glial cells
2 ways cells move:
radial migration: move out in a straight line
tangential migration: cells travel in right angles
Radial Unit Hypothesis process…
1. Ventricular zone = Generate Neurons Intermediate Progenitor (IP) divide to forms pairs of neurons
- Neurons Transverse Intermediate zone and Subplate Zones along RG cells
- Pass through deep layers and settle between Cortical Plate and Marginal Zone
Symmetrical Radial Division
Laterally – side way and therefore affects surface area
Asymmetrical Radial Division
Linear increase in radial coloumns results in an increase in cortical thickness
What determines position of neurons in neuronal migration?
Position of the neurons is determined by information in the VZ + a protomap in the SP and CP & is preserved by transient radial glial scaffolding
What impacts cortical thickness?
The number of IP and RG cells = cortical thickness
Human Vs. Rodent Brain
Outer sub-ventricular zone = larger
the division of the RG cells fromm sub-ventricular RG cells - which allows for ‘extra coloumns’ and a much larger cortex
oRG
oRG = non-epithelial radial-glial like cells – able to self renew and produce neurons similar to classic RG cells
oRG and classic RG divide asymmetrically to produce IP cells
IP cells divide once or twice to produce immature neurons
oRG cells and IP cells are known as ‘transit amplifying neurons’ as they amplify the number on neurons being migrated
THEREFORE contribute to the larger cortex in humans