Lecture 36 Outline of Last Lecture I. BDNFs (brain development neurotrophic factors) are necessary for proper developmentII. Zygote formation  embryo stage  fetal stageIII. Experiences, genes, hormones, and brain injuries all influence the development of neural circuitsIV. Neural plate pinches in and forms a neural tube that becomes the central nervous systema. 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 zoneV. Differentiated cells differ by changes induced through epigenetic alterationsa. Methylationb. Neurotrophic factorsOutline of Current Lecture I. Neural migrations begins at the subventricular zone and radiates outward to form layers of the cortexa. Neuroblast soma follows path of radial glial cellsb. Growth cones aid advancement outwardII. Cell adhesion molecules provide a surface to which growth cones can attach a. Tropic molecules are produced by target cells and increase axon affinityIII. Chemoaffinity hypothesis  there are guidance cue gradients that attract axons to their targetsa. Increased tropic molecule concentration closest to the target cellIV. 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 networka. Loss of synapses and less dendritic arborizationsb. Cortex becomes thinnerCurrent Lecture- Shortly after neurogenesis begins, neuroblasts begin to differentiate- Neural migrationo 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 surfaceo Cortex is “inside out”  innermost developed first, then outermostThese 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. NSCI 110 1st Editiono 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 directionso 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 coneso 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 degreeso 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 siteso Shows that there are guidance cue gradients used for axon targeting in developmento 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 growtho 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 lifetimeo Growth of dendritic spines where most synapses occur- Synaptic developmento 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 pruningo Apoptosis due to genetic signals, experience, hormones Parts of the cell “bleb” off after committing to a siteo 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 regionso These regions show an increase in gray mattero 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 yearso Some regions continue throughout adulthood- Glial developmento Gliagenesis begins after most neurogenesis is complete and continues throughout lifeo Myelination provides a rough index of cerebral maturation and is not complete until age 20o Region-specific  dorsal pathway, some language and motor areas show myelin maturation later in life- Sex differences in brain developmento Females show more rapid growth early ono Decreasing gray matter is due to apoptosis and synaptic pruningo White matter maturation delayed after