4_Ontogeny - Ontogeny: brain development in man From...

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Unformatted text preview: Ontogeny: brain development in man From conception to human being •Conception: a unique combination of genes •At day 14: (blastocyst) individual being (before, cells can develop to various tissues, eg placenta) •Until the 8th week: embryo •From the 9th week: foetus •At the 12th week: macrostructure of the brain completed ~ human life (Crevits, also the limit for legal abortion) Totipotent cells Development of neurons Pluripotent cells BERT => - ERNI => - Sox2 Fertilization Embryo Blastocyst Fetus When BERT (peptide) binds to ERNI (peptide), ERNI is inhibited. ERNI can no longer inhibit the Sox2 gene. Sox2 gives the comment for the development of cells to neurons. By blocking Sox2, other organs can develop earlier than the nervous system. outer layer => placenta inner cell mass => embryo From day 14 (blastocyst): individual being Prior to day 14, cells can develop to any type of cell and organ (eg placenta). •1 Embryonic development The ectoderm thickens along the dorsal midline to form the neural plate. The neural plate invaginates, forming a neural groove flanked by neural folds. The neural groove fuses dorsally and forms the neural tube. The neural tube differentiates into the CNS. Neural crest cells form some PNS structures. The anterior (rostral) end of the neural tube expands and forms the three primary brain vesicles In week 5 of embryonic development, secondary brain vesicles form Telencephalon and Diencephalon arise from the prosencephalon Mesencephalon remains undivided Metencephalon and Myelencephalon arise from the rhombencephalon •2 Summary of embryonic development Evolution and development (the recapitulation theory) Human brain at 5 weeks Brain of an adult fish Telencephalon Cerebral cortex Thalamus Hypothalamus Diencephalon Third ventricle Posterolateral growth of the telencephalon (cerebral hemispheres) encloses the diencephalon and superior aspect of the brain stem Coronal Section •3 Embryonic Brain Regions Brain Structures Present in Adult Cerebrum Cerebrum (cerebral hemispheres; includes cerebral cortex, white matter, basal ganglia) Forebrain Forebrain Thalamus Diencephalon Cerebral cortex Hypothalamus Diencephalon (thalamus, hypothalamus, posterior pituitary, pineal gland) Midbrain (part of brainstem) Midbrain Pons (part of brainstem), cerebellum Hindbrain Medulla oblongata (part of brainstem) Diencephalon Cerebral hemisphere Midbrain Hindbrain Midbrain Midbrain Pons Cerebellum Pons Medulla oblongata Hindbrain Medulla oblongata Spinal cord Cerebellum Forebrain Spinal cord Finally, the adult structure … Embryo one month old Fetus three months old There is also an evolution at cellular level Shore, R. 1997 •4 Ontogenie Phases in the development of the nervous system - Development of neurons (neurogenesis) - Migration of neurons to the periphery (cortex) - Growing of axon and dendrites - Sprouting of synapses (synaptogenesis) - Coating of myelin (myelination) - Pruning of extensions (pruning) - Programmed cell death (apoptosis) Hersenen in ontwikkeling Hersenen in ontwikkeling In de twintigste week van de zwangerschap heeft een foetus het overgrote deel van zijn totale voorraad hersencellen aangemaakt. Er is echter in het tweede deel van de zwangerschap en na de geboorte nog wel een zeer intense toename in het aantal synapsen tussen de verschillende neuronen. In de twintigste week van de zwangerschap heeft een foetus het overgrote deel van zijn totale voorraad hersencellen aangemaakt. Er is echter in het tweede deel van de zwangerschap en na de geboorte nog wel een zeer intense toename in het aantal synapsen tussen de verschillende neuronen. •Het is onmogelijk dat al deze verbindingen genetisch gecodeerd zijn. •Tijdens de eerste tien levensjaren vormen de ervaringen van het kind de basis voor een selectie tussen deze verschillende verbindingen. •Wat waarschijnlijk genetisch opgeslagen is, zijn de regeltjes die de neuronen volgen om verbindingen te maken… •De meest gebruikte synapsen worden versterkt, terwijl ongebruikte synapsen verdwijnen (pruning). Zo is een kind bij de geboorte in staat om alle fonemen van alle talen ter wereld uit te spreken. Na de leeftijd van tien maanden – zelfs nog voor het kind echt kan praten – kan het alleen nog de klanken uitspreken van de talen die het regelmatig hoort. •5 Possible roles for neurogenesis in adults Some areas of neurogenesis in the adult in subventricular zones, the hippocampus and along the cental canal of the spine 1. Neurogenesis plays a role in the encoding of new memories. 2. Stroke induces a transient increase in neurogenesis. the newly generated neurons seem to contribute to recovery of function. 3. Epileptic seizures trigger a burst of new neurons in the hippocampus, but seizure-induced neurons fail to properly integrate into the neural circuit. This “wiring problem” may underlie cognitive deficits that often do not manifest until many years later. 4. In depression, neurogenesis slows. This may help explain the long-recognized shrinkage of the hippocampus in people with long-lasting depression. In contrast, antidepressants increase neurogenesis, leading to speculate that this mechanism may explain the therapeutic effects of antidepressants. Brain development in adolescence Plasticity in adults A stoke patient with damage to the fibers transmitting information from the eyes to the cortex Although the macrostructure has become “adult”, the brain does not work like an adult’s. When images appeared in the preserved visual field, they appeared distorted. => hypothesis: distortions resulted from reorganisation in the deprived cortex (D. Dilks, J of Neuroscience, sept 5, 2007) •6 Brain development in adolescence Some brain changes relevant to adolescent behavior Puberty is a matter of genes… The “puberty gene” GRP54 => encodes for kisspeptine => hypothalamus: gonadotropin-releasing hormone (GnRH) => hypofysis: gonadotropins: LH (luteinizing hormone), FSH (follicle-stimulating hormone) => gonadal development => estrogen, progesterone, testosterone prefrontal prefrontal cortex cortex Prefrontal cortex (PFC) (judgment) is not fully developed until mid-20’s amygdala Amygdala and nu. accumbens (reward system) tend to dominate the PFC. nucleus nucleus accumbens accumbens Moreover, the reward system is less sensitive than in adulthood (demanding more reward to respond). This imbalance may lead to planned thinking, self-control impulsiveness , risk-taking => … drugs … Brain development from childhood through early adulthood Grey matter thickens in childhood but thins in adolescence: pruning the process of eliminating “overabundant” neurons Myelination and maturity Coating of myelin is not complete until age 20 Areas of the brain that regulate emotion, judgment, and impulse control myelinate during adolescence Myelination occurs earlier in girls than boys. This is why teenage girls seem more emotionally mature than boys Myelination folows an inverted U shape over livetime, peaking around 50. This is called wisdom Gogtay, N. et al., Proc. Natl.Acad. Sci. USA, 2004. 101, 8174–8179 Myelin: a fatty substance coating some axons, speeds electrical impulses White matter gains (due to advancing myelination) •7 Summary adolescent brain •Arond 12, the brain has the size, folding and regional specialization of an adult’s •Grey matter thins in a wave that begins at the back of the brain and reaches the front by early adulthood: use it or lose it! Substance abuse, Smoking, Drinking… •White matter is being gained, layers of myelin are added. The prefrontal region is the latest. •The prefrontal region is going to dominate the nucleus accumbens. have dramatic and erosive effects especially on the (adolescent) brain “The adolescent brain acts like an adult, but doing it much more difficult” The Human Brain: … Dendrites can grow at any age. Synaptic connections occur at any age; easier earlier in life Brain is adaptable (plasticity) => Use it or lose it •8 The Human Brain: AN ART WORK !!! Cerebral hemisphere: Dorsal View 1. Frontal pole 2. Superior frontal sulcus 3. Middle frontal gyrus 4. Superior frontal gyrus 5. Precentral sulcus 6. Longitudinal cerebral fissure 7. Precentral gyrus 8. Postcentral gyrus 9. Central sulcus 10. Postcentral sulcus 11. Occipital pole Cerebral hemisphere: Ventral View 1. Frontal pole of left cerebral hemisphere 2. Olfactory bulb 3. Olfactory tract 4. Orbital gyri and sulci 5. Straight gyrus 6. Temporal pole of left cerebral hemisphere 7. Olfactory trigone 8. Optic nerve 9. Optic chiasma 10. Anterior (rostral) perforated substance 11. Optic tract 12. Tuber cinereum with infundibulum 13. Oculomotor nerve 14. Mamillary body 15. Uncus of parahippocampal gyrus 16. Basis pedunculi 17. Basilar sulcus of pons 18. Trigeminal nerve 19. Abducens nerve 20. Pyramid of medulla oblongata 21. Facial nerve 22. Vestibulocochlear nerve 23. Glossopharyngeal nerve 24. Vagus nerve 25. Cranial roots of accessory nerve 26. Spinal roots of accessory nerve 27. Rootlets of hypoglossal nerve 28. Flocculus 29. Ventral rootlets of 1st cervical spinal nerve 30. Pyramidal decussation Cerebral hemisphere: Lateral View 1. Superior frontal gyrus 2. Superior frontal sulcus 3. Central sulcus 4. Precentral gyrus 5. Postcentral gyrus 6. Supramarginal gyrus 7. Angular gyrus 8. Postcentral sulcus 9. Parieto-occipital sulcus 10. Superior parietal lobule 11. Intraparietal sulcus 12. Precentral sulcus 13. Middle frontal gyrus 14. Inferior frontal sulcus 15. Inferior frontal gyrus 16. Anterior ascending ramus of lateral sulcus 17. Transverse temporal gyrus 18. Anterior horizontal ramus of lateral sulcus 19. Superior temporal gyrus 20. Superior temporal sulcus 21. Middle temporal gyrus 22. Stem of lateral sulcus 23. Inferior temporal sulcus 24. Inferior temporal gyrus 25. Preoccipital notch 26. Posterior branch of lateral sulcus 27. Triangular part of inferior frontal gyrus 28. Opercular part of inferior frontal gyrus •9 Cerebral hemisphere: Sagittal View 1. Medial frontal gyrus 2. Cingulate gyrus 3. Central sulcus 4. Paracentral lobule 5. Cingulate sulcus 6. Callosal sulcus 7. Subparietal sulcus 8. Precuneus 9. Parieto-occipital sulcus 10. Cuneus 11. Isthmus of cingulate gyrus 12. Lingual gyrus 13. Calcarine sulcus or fissure 14. Medial occipitotemporal gyrus 15. Collateral sulcus 16. Parahippocampal gyrus 17. Uncus of parahippocampal gyrus 18. Rhinal sulcus 19. Subcallosal area 20. Paraterminal gyrus 21. Indusium griseum 22. Rostrum of corpus callosum 23. Genu of corpus callosum 24. Trunk of corpus callosum 25. Splenium of corpus callosum 26. Fimbria of hippocampus 27. Cut surface of thalamus 28. Anterior (rostral) commissure 29. Interthalamic adhesion 30. Column of fornix 31. Septum pellucidum Cerebral hemisphere: Coronal View 1. Body of corpus callosum 2. Frontal horn of lateral ventricle 3. Septum pellucidum 4. Body of caudate nucleus 5. Columns of fornix 6. Anterior (rostral) commissure 7. Optic chiasma 8. Anterior limb of internal capsule 9. Globus pallidus 10. Lateral medullary lamina 11. Putamen 12. External capsule 13. Claustrum Cerebral hemisphere: Parasagittal View 1. Medial frontal gyrus 2. Cingulate sulcus 3. Cingulate gyrus 4. Central sulcus 5. Paracentral lobule 6. Callosal sulcus 7. Isthmus of cingulate gyrus 8. Subparietal sulcus 9. Precuneus 10. Parieto-occipital sulcus 11. Cuneus 12. Calcarine sulcus or fissure 13. Rostrum of corpus callosum 14. Genu of corpus callosum 15. Trunk of corpus callos 16. Splenium of corpus callosum 17. Choroid plexus in interventricular foramen 18. Interthalamic adhesion 19. Habenular trigone 20. Hypothalamic sulcus 21. Pineal body 22. Anterior (rostral) commissure 23. Tectum of midbrain 24. Mamillary body 25. Medial longitudinal fasciculus 26. Choroid plexus of 4th ventricle Brain Stem & Cerebellum 1. Oculomotor nerve 2. Interpeduncular fossa 3. Basis pedunculi 4. Basilar sulcus of pons 5. Motor (minor) root of trigeminal nerve 6. Sensory (major) root of trigeminal nerve 7. Abducens nerve 8. Middle cerebellar peduncle 9. Vestibulocochlear nerve 10. Facial nerve 11. Flocculus 12. Choroid plexus protruding through lateral aperture of 4th ventricle (foramen of Luschka) 13. Glossopharyngeal nerve 14. Vagus nerve 15. Accessory nerve 16. Olivary nucleus 17. Pyramidal tract 18. Hypoglossal nucleus 19. Pyramidal decussation •10 Cerebellum Spinal Cord 1. Flocculus 2. Uvula of vermis 3. Tonsil 4. Biventral lobule 5. Pyramis of vermis 6. Tuber of vermis 7. Inferior semilunar lobule •11 ...
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