NB II: Yuste C2 Flashcards
Parts of the Nervous System
Maps and brain modules
Modules are internally organized into maps. Neurons with different functions are systematically located in particular places within the module (ex: precise map between visual field and location of neurons in the visual cortex responding to those positions). –> Topographic maps.
Benefit of modules being organized in maps
Carefully laying out connections and corresponding functional properties might help minimize the total amount of wiring that the NS needs.
Stages of neural development
Neurulation
The pinching off of the neural tube from the epithelium of the embryo. The neural tube then floats in the embryo, and the proliferation of neurons from its walls makes the tube grow and change shape.
Patterning
When the uniform neural tube becomes specialized into regions. Involved are key regions of the embryonic NS called “organizers” which are regions that secrete molecules that can trigger/induce a specific change in other cells, creating molecular gradients.
Organizers
Secrete molecules, creating molecular gradients. Cells in the embryonic NS receive different concentrations of these molecules according to their positions along the three molecular gradients: rostro-caudal, dorsal-ventral, and medio-lateral. These molecular gradients create different combinations of molecular signals that are turned into intracellular cascades that activate TFs, which regulate gene expression –> gives rise to different cell types according to location along the three molecular gradients.
Neurogenesis
A step in which billions new neurons are generated in the ventricular zone of the neural tube. Neuronal progenitor cells move up and down, and their oscillatory movements lead to cell division, generating new neuroblasts each cycle. As they are born, these neuroblasts get pushes away from the centre of the tube to the periphery, making the tube thicker.
Migration
By climbing up the radial glial fibers that extend across the developing neural tube, neuroblasts migrate to away from the ventricular zone to the periphery/top. Then, they generate an axon.
Axonal growth and pathfinding
Each developing neuron extends an axon and navigates in the embryonic NS searching for a target neuron to connect with. This only happens in the NS. This is done by the growth cone.
Growth cone
A specialized structure at the tip of a growing axon. Its purpose is navigation via reading chemical signals. It is very specific. It is attracted forwardly chemo-attractant and repelled backwards by chemo-repellants.
Chemoaffinity hypothesis
The growth cone is repelled or attracted by chemicals/molecular markers secreted by or on the surface of other neurons (the molecules neurons secrete/have in their surface depends on their position in the 3D molecular gradient axes). The combination of attractive and repulsive chemical cues directs the growth cone to its correct target.
Synaptogenesis
The formation of synaptic connections. Incredibly precise and self-assembled.
Occurs when growth cones find the membranes from the body or dendrites of their target neurons. The growth cone and the target neuron exchange molecular signals, likely also mechanical ones, reacting accordingly.
Signals include inducing molecules from the axon, which generate expression and clustering of NT receptors –> sophistical post-S structure exactly opposed to axon.
Growth cone turns into mature pre-S terminal.
