Neurodevelopment Flashcards
Germinal Stage
The nuclei of the egg and the sperm fuse to form a zygote.
Zygote divides to form a cluster of homogeneous cells. Zygote continues to divide to initially form a morula then a blastocyte (200-300 cells).
Implantation occurs at approx day 6.
Embryonic Stage
By 2 weeks - differentiation of cells leads to the development of 3 distinctive cell layers:
ectoderm – nervous system
mesoderm – bone, muscle, connective tissue, skin
endoderm – digestive & respiratory tracts, liver, pancreas
Embryonic Neurodevelopment
Uneven rate of cell development forms midline. 2. Neural ridges on each side join to form neural tube. 3. Bulge of ectodern forms to create brain. Telencephalon and diencephalon - forebrain. Mesencephalon - hindbrain. Rhombencephalon - hindbrain. 4. Neural tube forms ventricles, central canal and spinal cord
Spina Bifida and Anencephaly
Spinal Bifida - failure of the closure of the neaural fold at the level of the spinal cord. Small openings often surgically corrected. Large openings - limb deformities. Prevented by folic acid. Anencephaly - brain fails to develop - results in stillborn.
Neurogenesis
Formation of neurones by the mitotic division of non-neuronal cells. Cells divide (mitosis) to form packed layer of cells (ventricular zone). Cells migrate out to there
Migration
Massive movement of neurones to distinct populations. Cells climb along radial glia cells. Chemically guided by cell adhesion molecules. Movement of cells from the cerebral cortex.
Differentiation
Once at the destination cells express genes. Cell-autonomous manner: processes directed from the cell itself. Induction: influences by neighbouring cells
Synaptogenisis
Growth cones at tip of axons and dendrites send fine outgrowths (filopedia) which adhere to the extracellular environment, contact and pull growth cone into the space
Neuronal Cell Death
Apoptisis - massive cell death. Pruning of cells. Chromosomes carry death genes e.g. Caspases. Cells that make connects survive - receive neurotrophic factors from target tissue promoting cell growth.
Synaptic Rearrangement
Active synapses take up brain derived neurotrophic factor from target cells. Transported to neurone soma. Stops cell death in early development. Stops synaptic pruning later.
Synaptic Rearrangement in Childhood
Thinning of grey matter on the exterior of the cortex. Occurs in a caudal-rostral direction with prefrontal cortex maturing in adolescence. Red/yellow - rapid thinning. Blue/purple - no thinning.
Schizophrenia features
Delusions (abnormal beliefs) Hallucinations (sensation of an experience that is not happening) Disordered thought (based on delusions and hallucinations) Abnormal behaviour.
Neurodevelopmental Model: Prenatal Stress
Prenatal second trimester: Migration of cells to more distal areas. Maternal stress leads to fetal exposure to cortisol which may lead to changes in brain development. Prenatal stress repgorams HPA axis. Links to Schizo because if there is a diminished feedback to the HPA axis this can cause it.
Neurodevelopmental Model: Childhood/adolescence
Synaptic Pruning: During adolescence large amount of grey matter is lost. If there is too much pruning in the frontal lobe. And incorrect cell location leads to decreased connectivity in childhood. At this stage we see the development of Schiophrenia.
Myelination
Starts at 24 weeks after conception. Continues after birth. Starts in spinal cord, spreads to hind, mid and forebrain. Sensory zones are myelinated before motor zones. 2 months - gropes to hold it. 4 months - grabs with whole hand. 10 months - uses pincer movements to hold.
