NSCI 110 1st Edition Lecture 36 Outline of Last Lecture I BDNFs brain development neurotrophic factors are necessary for proper development II Zygote formation embryo stage fetal stage III Experiences genes hormones and brain injuries all influence the development of neural circuits IV Neural plate pinches in and forms a neural tube that becomes the central nervous system a It is lined with neural stem cells that may differentiate into neuroblasts or glioblasts then further into specific types b Some remain in adults in the subventricular zone V Differentiated cells differ by changes induced through epigenetic alterations a Methylation b Neurotrophic factors Outline of Current Lecture I Neural migrations begins at the subventricular zone and radiates outward to form layers of the cortex a Neuroblast soma follows path of radial glial cells b Growth cones aid advancement outward II Cell adhesion molecules provide a surface to which growth cones can attach a Tropic molecules are produced by target cells and increase axon affinity III Chemoaffinity hypothesis there are guidance cue gradients that attract axons to their targets a Increased tropic molecule concentration closest to the target cell IV Dendritic growth occurs at a slower rate than axonal growth V Apoptotic signals are induced by genetic mechanisms whereas synaptic pruning is induced by loss of functionality in a neural network a Loss of synapses and less dendritic arborizations b Cortex becomes thinner Current Lecture Shortly after neurogenesis begins neuroblasts begin to differentiate Neural migration o Radial glial cell path making cell that a migrating neuron follows to its destination Begin at subventricular zone and radiate outwards to the pia mater Cell bodies remain in subventricular zone and project to brain s surface o Cortex is inside out innermost developed first then outermost These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o As the neuroblast soma moves dorsally the leading process has a growth cone tip that advances to maintains its length Filopods are spike like projections at the ends of growth cones At the ends of these developing axons that reach out to search for potential targets or sample intercellular environment Microtubules depolymerize polymerize to shorten and lengthen F actin cytoskeletal elements direct the cone in different directions o Cell adhesion molecules are proteins expressed on a cell s surface or in its environment can be secreted Provide surface for growth cones to adhere depends on filipodia s receptors genes expressed and origin Attract or repel growth cones o Tropic molecules are produced by targets being sought by the axons Cues that guide growth cones toward or away Concentrations increase closer to the target cell Chemoaffinity hypothesis test question on this o Sperry removed frog s eye and replaced it after rotating it 180 degrees o If vision restored to normal suggests nerves were guided to new sites of termination Vision direction of aim was inverted so nerves were guided back to the original sites o Shows that there are guidance cue gradients used for axon targeting in development o Surgery severs axons of neurons destined to the tectum Neurons wired to placed based on their original locations in the eye suggesting they have specific chemical affinities based on their origin Dendritic growth o Slower micrometers day than axonal growth millimeters day o Arborization branching Excess branching occurs in infants those that are used more are maintained throughout the individual s lifetime o Growth of dendritic spines where most synapses occur Synaptic development o Fifth gestational during pregnancy month simple synaptic contacts Progesterone o After birth synaptic development increases rapidly in the first year of life Programmed cell death and synaptic pruning o Apoptosis due to genetic signals experience hormones Parts of the cell bleb off after committing to a site o Cortex becomes thinner in a caudal rostral gradient a process mostly due to synaptic pruning less dendritic mass o Synapses that are not part of a functional network are pruned away in an experience dependent manner Gray matter thickness an important exception to the thinning of the grey matter in childhood is in major language regions o These regions show an increase in gray matter o Increase in thickness of language related regions mostly in the left hemisphere Neuronal maturation period of time involving growth of dendrites axons and synapses o Goes on for years o Some regions continue throughout adulthood Glial development o Gliagenesis begins after most neurogenesis is complete and continues throughout life o Myelination provides a rough index of cerebral maturation and is not complete until age 20 o Region specific dorsal pathway some language and motor areas show myelin maturation later in life Sex differences in brain development o Females show more rapid growth early on o Decreasing gray matter is due to apoptosis and synaptic pruning o White matter maturation delayed after gray matter