Chapter 8 - Brain Development Flashcards
ontogenetic development
the development of the individual human from a sperms and egg cell. the development of the nervous system and behavior go hand in hand. after fertilization, the following distinction can be made:
- zygote: from conception
- embryo: from week 2
- fetus: from week 8-9
- baby: from birth
spina bifida
a birth defect caused by the neural tube not closing sufficiently, in which the spine and spinal cord are not formed properly. can be prevented by taking folic acid while pregnant
15th day after fertilization
the emerging embryo resembles a fried egg: a structure formed by several sheets of cells with an elevated spot in the middle called the embryonic disk
23rd day of fertilization
anterior neural folds close to form the brain. if it does not happen properly, it leads to anencephaly, which is a series of severe abnormalities in the brain that are fatal once the baby is born. the rest of the tube gradually develops into the spinal cord
25th day of fertilization
forebrain, midbrain, and hindbrain are visible.
7-9 months
the gyri and sulci are formed 7 months after conception. at 9 month, the brain has the overall shape of an adult brain, but its cells are different
neural stem cells
neural stem cells in the neural tube have an extensive capacity for self-renewal. in adult humans, neural stem cells line the ventricles, forming the sub-ventricular zone
functions of stem cells
in addition to self-renewal, neural stem cells have the function of giving rise to progenitor cells (pre-cursor cells), which can also divide. these cells produce neuroblast and glioblast cells, which cannot divide
neurotrophic factors
chemicals that can turn on (express) certain genes that instruct the cell to develop in a specific way
gene methylation
a chemical process that turns off specific genes
summarized
- when a stem cell divides, it produces two stem cells: one dies and the other divides again (this is a cycle)
- stem cells develop into precursor cells, which can also divide
- progenitor cells produce non-dividing cells, neuroblasts and glioblasts
- neuroblasts develop into specialised neurons, and glioblasts develop into specilized glial cells
7 stages of brain development
- cell birth (neurogenesis)
- cell migration
- cell differentiation
- neural maturation
- synaptogenesis
- apoptosis and synaptic pruning
- myelination
- cell birth (neurogenesis)
this is the formation of nerve cells from stem cells that happen in the neural tube, up to about 25 weeks after conception. all neurons are produced except hippocampus, in which neurogenesis continues throughout lifetime.
- cell migration
from the neural tube, the cells travel to the right place, which goes from the inside to the outside. cells know where to go because of redial glial cells, which guide them from subventricular zone to the cortical surface
- cell differentiation
the brain relies on a general-purpose neuron that matures into a specific cell type in a specific location when exposed to local environmental chemicals. this happens when the cells reach their destination. then chemicals in the environment determine what type of specialised cell they should become by turning on certain genes
- neural maturation (from week 20)
neurons begin to develop by growing dendrites and then axons. dendrites grow, and axons look for targets on which to form a synapse. the development of dendrites starts with the creation of branches (dendritic aborization) and ends with the growth of dendritic spines.
- synaptogenesis
formation of synapses. starts around 5 months after conception. after birth, synaptogenesis accelerates, creating many new synapses.
- apoptosis and synaptic pruning
first there is an overproduction of neurons, and then unnecessary cells die (apoptosis). the synapses on the remaining neurons are either included in a functional network and reach adulthood, or they are eliminated through synaptic pruning.
apoptosis
pre-programmed cell death due to dependence on neurotrophic factors
- myelination
the formation of myelin around axons. increased connectivity in the default network is related to higher intelligence. this continues till adulthood. myelination is an index of cerebral maturation. white matter increases, gray matter decreases, but not in language areas, where it increases
birth to 18-24 months (piagets stages of cognitive development)
stage 1: sensorimotor
experiencing the world through senses and actions
- object permanence
- stranger anxiety
about 2-6 years (piagets stages of cognitive development)
stage 2: pre-operational
represents things with words and images but lacks logical reasoning
- pretend play
- egocentrism
- language development
about 7-11 years (piagets stages of cognitive development)
stage 3: concrete operational
thinks logically about concrete events: grasps concrete analogies and performs arithmetical operations
- conversation
- mathematical transformations
about 12+ years
stage 4: formal operational
reasons abstractly
- abstract logic
- potential for mature moral reasoning
neural (cortical) plasticity
brain is a flexible organ, connections are not fixed
role of the environment
an enriched environment leads to the formation of more synapses
testosterone
testosterone is an androgen (male sex hormone), when it is present, it leads to a male; when it is not present, it leads to a female.
estrogens
female sex hormones and involved in menstrual cycles and pregnancy
chemoaffinity hypothesis
states that specific molecules in different cells in various midbrain regions give each cell a distinctive chemical identity
