Neurodevelopment Flashcards
Notochord
. Central event in gastrulation
. Distinct cylinder of mesodermal Ellis that condenses at midline of mesoderm and extensor from mid-ant. To post. Aspect of the embryo
. Generated by primitive pit surface indentation that elongates to primitive streak
. Disappears once early development is complete
. Sends inductive signals to overlying ectoderm that causes cells to differentiate into neural precursor cells
Neuroectoderm
. Ectoderm that lies immediately above the notochord
. Will give rise to entire nervous system
Neurulation
. Midline ectoderm thickens into distinct columnar epithelium (neural plate)
. On 18th day the neural plate invaginates along central axis to form neural groove that has neural folds on each side
. By end of 3rd week, the neural folds start to approach each other and fuse at midline converting neural plate into neural tube
Neural crest cells
. Cells at lips of neural fold that lie btw neural tube and overlying ectoderm
. Migrate away from neural tube and give rise to PNS and other types fo peripheral cells
Neural tube
. Walls thicken to rom brain and spinal cord
. Lumen is converted into ventricular system of brain and central canal of the spinal cord
Spinal cord formation
. Proliferation/differentiation of neuroepithelial cells in developing spinal cord produce thick walls and thin roof/floor plates
. Differential thickening of lat. walls produces sulcus limitans (shallow longitudinal groove) on death side that separate alar plate (dorsal part) from basal plate (ventral part)
. Plates produce longitudinal bulges through length of developing spinal cord
Alar plate
. Cell bodies form dorsal gray matter (dorsal gray horns in transverse sections)
Basal plate
. Cell bodies form ventral gray matter( ventral horns in transverse section)
Spinal ganglia
. Pseudounipolar neurons in spinal ganglia
. Derived from neural crest
. Form swellings on dorsal roots of spinal nerves (dorsal root ganglia)
Brain formation
. Fusion o neural folds in cranial region and closure of rostral neuropore
. Form forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon) as primary brain vesicles
Forebrain components
. Split during 5th week
. Telencephalon
. Diencephalon
Hindbrain components
. Metencephalon
. Myelencephalon
Flexures created during brain formation
. Midbrain flexure: formed by brain growing rapidly and bending ventral w/ head fold
. Cervical flexure: at junction of hindbrain and spinal cord
. Pontine flexure: between midbrain and cervical flexures in opposite directions
Brain primary vesicle form what components of brain?
. Myecephalon: medulla oblongata
. Metencephalon: pons and cerebellum
. Midbrain: midbrain
. Forebrain: diencephalon and telencephalon
Neurogenesis
. Mitotic division of non-neuronal cells to produce neurons
. Takes place in innerlayer of neural tube
. Cells gradually form closely packed layer of cells (ventricular zone)
. Eventually cells leave ventricular zone and begin transforming into neuron of glial cell
Cell migration in nervous system development
. Massive movement of nerve cells to establish distinct nerve cell population
. Cells have to move over long distances to fill out brain
Cell differentiation in neuronal architecture
. Cells reach destinations then begins o express particular genes for a specific phenotype
. Fate fo differentiating cell depends on where in the brain it is and when during development it is occurring and what the cell’s neighbors are doing
. Considered hallmark of vertebrate development
Patterning along AP axis
. Ant. Portion of neural tube undergoes series of swellings, constrictions,a Nd flexures
. Caudal portion retains simple tubular structures and forms spinal cord
. Development characterized by sequential and hierarchical expression of different TFs at different times and in different parts of embryo
Main factors in specifying properties of specific types of neurons, glia, and other cells
. Combination of transcription factors (TFs) they express
Hox genes
. Conserved among animals
. Key role in assigning regional identities along AP axis
. Segmental pattern of Hox genes expression creates structure appropriate to particular AP position in the embryonic hindbrain while other 2 genes for TFs ems and otx play major roles in development of forebrain
. Expression of emx gene is restricted to the forebrain region and stop abruptly at its boundary w/ midbrain
Patterning of neural architectures along AP and dorso-ventral axes
. Floor plate (specialized glial cells) along ventral midline
. Basal region of neural tube gives rise to motor neurons
. More dorsal alar regions give rise to interneurons
. Region most dorsal forms roof plate and neural crest
Sonic hedgehog
. Signaling Protein
. Initially produced and secreted by cells of notochord just ventral to neural tube
. Ventral cells experience most sonic hedgehog expression to the ventrodorsal gradient is established in neural tube w/ high conc. In ventral regions
BMP and Wnt proteins
. Generates dorsoventral gradient in roof plate
. Induces differentiation of dorsal regions of developing spinal cord
. Specialized differentiation is achieved through expression of particular combo of TFs that determine regional identity throughout CNS
Synaptogenesis
. Establishment of synaptic connections as axons and dendrites grow
. Begin making synaptic connections w/ one another
Neuronal cell death
. Selective death of many n. Cells
. Normal part of development
. Cell death is crucial phase of brain development
. Neurons compete for connections to target structures
. Cells w/ adequate bypasses remain, those w/o a place to form synaptic connections die
Synapse rearrangement
. Loss of some synapses and development of others to refine synaptic connections
. Some synapses formed early in development are later retracted
. Takes place after period of cell death
. Which synapses are retained sesults from competition for tropic factors during development
