S2 W3 Prenatal development Flashcards
Natal
of one’s birth, processes of birth/pregnancy
Prenatal development
development of huans before they are born
Postnatal development
development of human after they are born, often specifically referring to infancy
Neonate
an infant who is less than a month old
Prenatal Periods
1-Germinal period (single cell zygote => morula =>blastocyst) = conception to attachment to uterine wall. 0 to 10 days
2-Embryonic period (embryo) = attachment to uterine wall ends in the 8W when all major organs have taken primitive shape. 2 to 8 GW
3-Fetal period (fetus) = largest amount spent in this period.9GW to Birth
3 gerlan layers
Endoderm = the inner lining of some systems and some organs such as the liver and pancreas.
Mesoderm = bones, muscles, the heart and circulatory system, and internal sex organs.
Ectoderm = skin, the brain, and the nervous system
What is an ectoderm?
It becomes a neural plate, which differentiates into cells, that will become the fore/mid/hindbrain. Neural plate folds to become neural tube.
Prenatal indirect methods
Presenting loud sounds on surface of abdomen and asking mothers to report fetus movement.
Inferences from non-human animal models.
Autopsy of human embryos and fetuses.
Inferences from studies measuring the perception and memory of neonates.
=> Practical, ethical issues
Prenatal direct study methods
Fetal ultrasound, brain acitivty using fMRI
Phases of Brain development
Neurulation / Neural plate induction
Neurogenesis / Neural proliferation
Migration / Neuronal migration
Maturation / Dendrite and axon growth
Synaptogenesis / Synapse formation
Apoptosis / Neuronal death
Myogenesis / Formation of myelin
Neurulation neural plate induction
The ectoderm becomes the neural plate - a patch of tissue on the dorsal surface of the embryo that will become the nervous system.
Development induced by chemical signals.
Growth factors - several chemicals produced in developing and mature brains that stimulate neuron development and help neurons respond to injury.
Impact: neural tube defects (NTD)
Genetic/environmental factors: increase risk of NTDs. Maternal folic acid supplements have been demonstrated as effective in reducing the risk of NTDs
Neurogenesis
Two types of cells: neurons, glial cells ( = outnumber neurons, nourish, repair and myelinate neurons, crucial for development.)
Neural proliferation
neurogenesis continues after birth. Proliferation is a part of neurogenesis - i.e., the generation of new cells via mitosis. The multipotent cells turn into neuroblasts and glioblast which then become the neurons and glial cells during migration
Migration/neuraonal migration
Radial glial cells: act as guide wires for the migration of neurons. Migrating cells are immature, lacking dendrites. Cells that are done migrating align themselves with other cells and form structures (i.e., they aggregate).
neuronal migration disorder (NMD)
characterized by neurological deficits in childhood. Most common symptom of NMD is intractable epilepsy.
Causes (can vary): genetic in origin and multiple genetic disruptions/mutations have been associated with NMD.
Maturation/Dendrite and axon growth
Once migration is complete and structures have formed, axons and dendrites begin to grow to their ‘mature’ size/shape.
Axons (with growth cones on end) and dendrites form a synapse with other neurons or tissue (e.g., muscle).
Growth cones and chemo-attractants are critical for this stage
Synaptogenesis / Synapse formation
multi-stage process. Dependent on the presence of glial cells – especially astrocytes.
Therefore, occurs at about 23 weeks of gestation after migration. Many synapses form randomly (as axons and dendrites meet).
Chemical signal exchange between pre- and postsynaptic neurons is needed.
Neuronal death, apoptosis
Between 40-75% neurons made, will die after migration – death is normal and necessary (within reason). Neurons die due to failure to compete for chemicals provided by targets.
Neurotrophins: promote growth and survival, guide axons, stimulate synaptogenesis.
Myogenesis / Formation of myelin
Myelination begins in PNS at 2MG. Motor roots become myelinated before sensory roots. 3rd trimester myelinatin occurs in CNS (first in sensory tracts).
Synaptic prunning
Pruning improves the efficiency of the brain and the transmission of signals between neurons. Synaptic pruning is relatively slow prenatally and is most rapid following the 2nd year of life (Konkel, 2018).
Fragile-X syndrome is a genetic disorder that:
results in developmental delays, learning disabilities, and behavioral problems;
is caused by a defective FMR1 gene which suppresses production of proteins that stimulate pruning.
Excess synapses are not pruned sufficiently. ‘Noise’ in the neural system causes symptoms such as attention deficit symptoms
prenatal learning
At 6 months gestation, fetuses = have the capacity to learn despite immaturity of the foetal nervous system, show basic forms of memory (e.g., habitation of response to repeated auditory stimuli).
