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Flashcards in Development of Nervous System Deck (30)
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What is gastrulation

- Conversion of bilaminar embryo into trilaminar embryo
- Migration of superficial epiblast cells (totipotent) interiorly creates a third layer


What are the steps involved in gastrulation

1. Epiblast cells migrate to primitive streak, form longitudinal axis
2. Cells push through primitive groove and form mesoderm
3. Mesoderm spreads between epipvastic and hypoblastic layers of embryonic disc
4. Areas where embryonic mesoderm cells are absent form cloacal and oral membrane


What is organogenesis

- Formation of body organs and organ systems
- Endoderm, mesoderm and ectoderm


What does the endoderm form

- Inner layer from hypoblast
- GI tract / associated glands
- Lungs
- Urinary tract / mucosae
- Thyroid cells
- Pancreatic cells


What does the mesoderm form

- Middle layer, somites paired mesodermal blocks
- Muscles
- Bones
- Circulatory system
- Tubule cells of kidney


What does the ectoderm form

- Outer layer, from epiblast
- Neurulation causes differentiation to brain and spinal cord
- NS
- Skin / epidermis
- Hair


What are the phases of neurodevelopment (4)

1. Neural plate formation and induction (delineation of ectoderm cells)
2. Neural proliferation, migration and aggregation
3. Axon growth and synapse formation
4. Cell death and synapse rearrangement


What occurs in neurulation (2)

- Neural plate develops neural folds to form neural tube
- Bending: 3 hinge points, median hinge point (over pre-chordal plate) and paired dorsolateral hinges
- Folding: Rotation of plate around hinge points, elevation (folding MHP) and conversion (folding DLHP)


What are the steps in neural tube formation (neurulation)

1. Cells migrate cranially from primitive node to form notochord
2. Notochord induces ectodermal cells to elevate and thicken, forming neural plate
3. Folds fuse to to elevation of hinge points and form neural tube (closes from middle outwards) with neural crest above
4. PNS develops from neural crest
5. Placodes give rise to ears and nose


What is BMP signalling

- Bone morphogenetic proteins
- Potent epidermalising agent
- Inhibition is required for neural crest induction and signalling
- Initially BMP promotes formation of non-neural ectoderm
- Inhibition is required to establish primitive neural tissue (neuroectoderm)


What is Wnt signalling

- Secreted signalling proteins
- Promote cell cycle progression in stem and progenitor cells
- Associated with BMP signal activation in dorsal spinal cord


What is a neural tube defect

- Failure of neural tube to close (1 in 500)
- Tube closes from the middle and extends anteriors / posteriorly


What are examples of neural tube defects

- Anencephaly (defect in anterior closure)
- Spina bifida (defect in posterior closure, leg weakness, orthopaedic abnormalities, paralysis)


Why is folate important in pregnancy

- Folate is a water soluble vitamin that is present in food (green leafy vegetables)
- Important in the synthesis of DNA, DNA repair and methylation of DNA
- Prevents NTD births among most women who have previously had NTD affected births
- Folate supplements of 0.4-5 mg per day suggested


What occurs during neural proliferation, migration and differentiation (2)

- Proliferation: Swellings of anterior brain become forebrain, midbrain and hindbrain, daughter cells become fixed
- Migration: Slow movement guided by radial glia, soma and immature axons, aggregation occurs once complete
- Differentiation: Cells location determines differentiation (function / precise connections), active


What occurs during axonal growth (3)

- Once migration is complete and structures have formed (aggregation)
- Axons and dendrites grow to their mature size / shape
- Growth cones guide axons with long range (chemo repulsion / attraction) and short range (contact repulsion / attraction) cues
- Fasciculation (grouping of axons)


What occurs during axonal synaptogenesis (3)

- Axons (with growth cones) and dendrites form synapse with other neurons or tissue (muscle)
- Formation of synapses depends on presence of glial cells (especially radial / astrocytes)


Describe what happens with neuronal death and apoptosis (4)

- Controlled cell death
- Responsible for shaping organs and tissue
- Unwanted cells are removed (evolution)
- 40-75% of neurons die after migration
- Death due to neurotrophin signals, lack of signals causes apoptosis (extrinsic)
- Survival or neurite out growth)


What postnatal growth occurs in the CNS

- Synaptogenesis
- Increased dendritic branches
- Myelination (prefrontal cortex continues into adolescence)
- Increased recovery from injury in adolescence in comparison to an adult


What is foetal alcohol syndrome

- Alcohol inhibits all stages of brain development
- Promotes neuronal cell death
- Infant show problems with sleep, muscle tone and sensory information processing
- Children are hyperactive, poorly coordinated
- Adolescent / adult show poor judgment, problems with arithmetic and frustration/anger


What are the primary brain vesicles

- Develop at rostral (anterior) end of neural tube
- Forebrain / Prosencephalon: Telencephalon and diencephalon
- Midbrain / mesencephalon
- Hindbrain / Rhombencephalon: Metencephalon and myelencephalon


What is the forebrain

- Prosencephalon
- Conscious awareness and cognition, voluntary actions and movement
- Sensory and motor connections
- Telencephalon (cerebrum, cerebral cortex)
- Diencephalon (thalamus, hypothalamus, epithalamus)
- Secondary vesicles sprout either side (hemispheres), optic vesicles invaginate, remaining is diencephalon


What is the midbrain

- Mesencephalon
- Relay and processing of information from cerebral cortex to spinal cord
- Tectum (dorsal surface, superior / inferior colliculus), cerebral aqueduct, tegmentum (red nucleus / substantia nigra)


What is the hindbrain

- Rhombencephalon
- Coordinates respiratory rhythm, motor activity, sleep and wakefulness
- Rostral portion becomes metencephalon and myelencephalon (medulla oblongata / brain stem)
- Pons: Bridge from cerebellum to medulla
- Medulla: Sensory and motor functions
- Cerebellum: Movement, body's position in space, best sequence of muscle contraction


What are specialities of the human brain

- Olfactory Bulbs: Smaller
- Brain Flexures: Cervical (brain stem / spinal cord), midbrain (pushes mesencephalon up) and pontine (4th ventricle)
- Convolutions: Increased SA, gyri / sulci, massive expansion


What is hydrocephalus

- Enlargement of ventricles due to increased CSF
- Leads to compression atrophy
- Congenital (ventricular abnormality) or acquired (fibrous adhesion blockage)
- Increased ICP, weakness, reduced coordination, dementia, brain damage


What is differentiation of the spinal cord

- Proliferation occurs in 2 zones
- Characteristic butterfly shape of gray matter
- Lateral walls of tube thicken


What are 3 important aspects of a differentiated spinal cord

- Sulcus Limitans: Separates gray matter into dorsal alar and ventral basal plates
- Alar Plate: Neuronal cell bodies, dorsal gray matter, receive and relay input
- Basal Plate: Cell bodies form ventral matter, motor fibres to skeletal muscle, ventral roots


When does development of PNS occur

- Cells from neural crest migrate pat neighbouring somites to numerous locations
- Form dorsal root ganglia (sensory), sympathetic and parasympathetic ganglia


What is SHH

- Sonic Hedgehog
- Controls important developmental processes
- Secreted from the notochord and floor plate
- Promotes proliferation, downstream activation of Gli3
- Mutations: Cause of severe holoprosencephaly (HPE), lead to cyclopia, failure of axial midline to form