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NE101 Lecture Notes

Neural cell types evolved by repurposing existing

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Most synaptic proteins are ancient and predate functioning nervous systems! Neural cell types evolved by repurposing existing cellular machinery that did not have a cell-to-cell signaling function. Synapses arose when cells evolved the ability to form close association and send signals directly to this existing machinery. Evolution of neurons – main points (1) Lots of ancestral cellular machinery for detecting and responding to stimuli (ligands) already in place in common ancestor of all animals. (2) Neurons appear when cells evolve the ability to send signals to other cells using this machinery. (3) Neural evolution in bilaterians is a process of elaboration and increasing complexity. Evolution of Brains earliest nervous systems were decentralized like the nerve nets of modern cnidarians evolution of body symmetry was associated with changes in sense organ distribution: bilaterally symmetrical animals evolve a “front” (head), with most sense organs, along with a “back”, “top”, and “bottom”. Cephalization: the related evolutionary trend of increasing concentration of nervous tissue in the head, leading to animals with centralized brains. Faster transduction/processing of sensory information More energetically efficient Brain organization varies among animals But ancestral bilaterians had brains (i.e., protostome and deuterostome brains are homologous) Universal principle I: regionalization specialized regions to process different stimuli compartmentalization in the nervous system ex. olfactory system Universal principle II: serial and parallel organization sensory information is processed serially in dedicated pathways in the brain. different modalities are processed in parallel and later integrated in higher-order centers. Universal principle III: development the expression of developmental patterning genes is highly conserved in animal brains gene expression refers to the pattern of when and what genes are “turned on” or “turned off”. ex. Pax6 is expressed in developing mice where eyes will develop Truine brain hypothesis (1960s) part of your brain there is a Reptilian complex (e.g. basal ganglia) → distant past part of your brain Paleomammalian complex → more recent part of your brain Neomammalian complex → most recent Vertebrate brain evolution = steadily increasing complexity and addition of new regions, culminating in the “best” kind of brain Critiques: (1) Implicitly considers evolutionary process to be linear w/humans at the top. (2) Implies mammals evolved from “simple” reptiles, which is not the case; mammals are sister to the reptiles. (3) Reptiles have limbic and cortical structures, all mammals posses a neocortex.
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(4) Reptile behavior is not simple and stereotyped.
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