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🤰 Prenatal Neurodevelopment | ||||||||||||
| Prenatal Neurodevelopment - Neural system development from 0 to 9 months. - Learn about Neuro development in Childs. Topics, Stages, prenatal, postnatal, birth, disorders, evaluation, clinic, hospital, neurodevelopmental therapy. - Find neuroscience, neurology and neurodevelopmental information for our lives. | ||||||||||||
Prenatal NeurodevelopmentThe prenatal period sets the foundation for all future brain architecture. Key stages include neural induction, proliferation, migration, differentiation, synaptogenesis, and programmed cell death. • Neural Induction and Patterning During weeks 3–4 of gestation, the ectoderm forms the neural plate, which folds into the neural tube. Signaling gradients of sonic hedgehog (SHH) and bone morphogenetic proteins (BMPs) pattern the tube’s dorsal–ventral and rostral–caudal axes. - SHH from the notochord directs ventral cell fate. - BMPs from the roof plate guide dorsal identities. - Transcription factors (e.g., OTX2, GBX2) define forebrain and hindbrain regions. • Proliferation and Migration Neural progenitors in the ventricular zone divide symmetrically then asymmetrically to produce neurons and glia. Newborn neurons migrate along radial glial fibers or tangential pathways to their target layers. - Radial migration builds the six-layered cerebral cortex. - Tangential migration seeds interneurons into the cortex. - Disruptions can lead to cortical malformations (e.g., lissencephaly). • Differentiation and Synaptogenesis Once neurons reach their destinations, they extend axons and dendrites under guidance from netrins, semaphorins, and ephrins. Synaptogenesis—formation of synaptic contacts—peaks during the third trimester. - Neurotrophic factors (BDNF, NGF) support survival and growth. - Filopodia on dendritic spines survey for presynaptic partners. - Overproduction of synapses allows experience to select functional circuits. • Programmed Cell Death and Pruning Apoptosis eliminates roughly 50% of neurons born prenatally and postnatally. Microglia phagocytose debris and sculpt synaptic connections, refining emerging networks. - Caspase activation triggers cellular dismantling. - Synaptic pruning reduces redundant connections. - Proper pruning is essential for efficient signal transmission. | ||||||||||||
Prenatal Development of the Neural SystemPrenatal NeuroDevelopment is related with the physiology of egg and sperm, intrauterine environment, genetic transmission, errors, mutations. Psychosocial environment influences via mothers’ stress hormones and self-care behaviors. 2 weeks to 6 months of gestation: Neurons divide and multiply. NO new neurons develop postnatally. Problems : fewer neurons at beginning of life (e.g., MR) 6 weeks to 6 months of gestation: Neurons migrate. Move from central ventricle toward skull, forming layers, each built on top or earlier ones. Problems : neurons in wrong layer of brain; abnormal connections 6 weeks to 6 months of gestation: Axons form basic links. Use genetic blueprints and chemical cues Neurons send electrical signals (from dendrite to end of axon) and chemical signals (from end of axon to nearby neurons or muscle cells). Problems : seizures, mood/attention problems Neural Tube Development: during 3rd and 4th week gestation, the dorsal ectoderm invaginates to form a closed midline neural tube that eventually gives rise to the CNS. Defects in closure are magnified throughout gestation. Ectoderm forms CNS and skin. Mesoderm forms coverings of CNS (meninges, vertebrae, and skull). Neural tube
| Development of neural tube: Starts from 18 days - CNS and PNS develop from midline ectoderm layer of fertilized egg. Neural plate appears from dorsal ectoderm. In the center of the plate, the cells on edge become narrower on inner surface, while those surrounding become narrower on outer surface, forming neural groove formed of neural folds. This gradually deepens, and folds over onto itself. It starts to close starting at midpoint and extending in both rostral and caudal directions. As it closes, there are two open ends (neuropores), which close at 25 days gestation, forming neural tube. Anterior end gives rise to brain, posterior end forms spinal cord. Process of conversion from open groove to sealed tube is neurulation. Neural tube defects occur third to four weeks gestation: neural tube has difficulty closing (anterior- anencephaly; caudal- spina bifida). Neural crest cells are adjacent to neural tube. They are free of overlying ectoderm and form irregular bundle of tissue surrounding tube. These clumps of cells migrate and differentiate to form ganglia. Regional DevelopmentDevelopment of the neural system by regions Three vesicles develop at anterior end of neural tube. Prosencephalic (becomes forebrain), mesencephalic (becomes midbrain), rhombencephalic (becomes hindbrain). 5th week of gestation. prosencephalic vesicle divides into telencephalon and diencephalon rhombencephalic vesicle divides into metencephalon and mylencephalon 7th week of gestation . telencephalon transformed into cerebral hemispheres diencephalon into thalamus and related structures metencephalon into cerebellum and pons myelencephalon into medulla oblongata In vestigial form, the neural tube becomes the cerebral ventricles and cerebral aqueduct Caudal (tail end) becomes spinal cord, elongating and developing into segments, each of which is associated with sensory and motor innervation Spinal cord keeps remnant of neural tube as central canal In cord, neural tissue desegregates into two main bodies of neurons - dorsal (posterior) horns and ventral (anterior) horns, divided by sulcus limitans Dorsal horns, also called alar plate, receive axons from dorsal root ganglia and involved in sensory events Ventral horns, also called basal plate, contain cell bodies of axons that innervate muscles and considered part of motor system | CortexDevelopment of Cortex The corticogenesis process begins at the 6th week of gestation. 6th week of gestation - basal ganglia visible 8-10 gestation weeks - early cortical plate forms from migrating cells; four layers of cortex are visible (ventricular, subventricular, intermediate, and marginal) As cortex develops, first expands anteriorly to form frontal lobes, then dorsally to form parietal lobes, then posteriorly and inferiorly to form temporal and occipital lobes Posterior and inferior expansion pushes cortex into a C shape, which shapes many of the underlying structures (lat vents, head of caudate of BG, hippocampus) 5th month gestation - increasing number of cortical cells causes smooth surface of brain to develop pattern of convolutions and sulci Pattern of convolutions and sulci - primary, then secondary, then tertiary. hippocampal sulcus: 13-15 weeks; parieto-occipital, calcarine, olfactory bulb sulci: 19 weeks; sylvan (lateral) and rolandic (central) sulci: Spreen says 24 weeks but other article says 14 weeks; secondary sulci (first temporal sulcus, superior frontal sulci): 28 weeks; tertiary not formed until third trimester and continue development after birth Gyral pattern of adult present at birth. Gyri and sulci patterns form after neuronal migration and reflect processes of neuronal specialization, dendritic arborization, synaptic formation, and pruning Formation of gyri signals that intracortical connections are established Extreme alterations suggest deviations in cortical connections and potential deficits: polymicrogyria - small, densely packed gyri associated with LD, MR, and epilepsy 6th month gestation - cortical plate thickens due to migrating neurons and more layers are formed, giving cortex final six-layered composition Development of Intercerebral Commissures
| Growth is slow and related to maturation of association cortex. First commissural fibers cross in rostral end of forebrain at 50 days gestation, creating anterior commissure and hippocampal commissure Fibers of CC cross develop in parallel with various cerebral lobes and process not complete until after birth Failure results in agenesis of CC Development of Ventricles.
| Cavities within cerebral vesicles of neural tube form vents and central canal of spinal cord Cavities of cerebral vesicles differentiate into two lateral vents, aqueduct of sylvius, fourth vent Embryology studies the embryological development of the human brain.
| FAS - The fetal and young child nervous system: the story of the development and maldevelopment of the brain.
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