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Lecture 1.docx

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University of Toronto Scarborough
Rutsuko Ito

Organizational principles of the mammalian brain  synaptic organization of the brain Course outline  basics of electrical activity in neuron  neurotransmission: pre-synaptic and post-synaptic mechanisms  synaptic integration and neuromodulation  synaptic organization of thalamus o midterm test  synaptic organization of basal ganglia  synaptic organization of hippocampus  synaptic plasticity and learning  synaptic organization of neocortex o midterm test  synapses in network: o oscillations  optogenetics: o light activated brain Course objectives  you will understand the core principles of how the brain is organized o at the systems level o at the circuit level o at the synaptic level  to achieve complex information processing  you will understand how electrical signals are generated and transmitted throughout the brain  you will understand how synaptic organization in a particular brain area is related to its function  you will understand the methodologies used in the field of cellular neurobiology  you will be able to read critically, and appreciate at a fairly sophisitcated level, articles written in the field of cellular neurobiology Evaluation  2 midterms o each 25% o multiple choice questions o short answers  Final exam o multiple choice questions from lectures 9 - 10 o essay question  long answer question  more structure o critical analysis of paper  paper will be posted two weeks before the exam  2 practice articles throughout the course, one of which was the paper from last year's final exam Resources  posting of lecture / reading / supplementary material  discussion forum on lecture content and critical analysis of empirical papers  announcements  email: o [email protected]  office hours: o tuesdays 1-3pm in sw627 The brain  human brain: o 100 billion neurons o 100 quadrillion synapses  how is the brain organized with so many neurons Brain organization  connections in monkey visual cortex o highly intricate and organized Study of brain organization  defining levels of organizations o brain is organized by different brain regions Level of organization  behavioral system: 10 cm o interregional system: 1cm  regional circuits: 1mm  neurons: 100um o synapse: 1um  molecule / ion channels: 1A  genes  systems neuroscience o behavioral system o interregional system o regional circuits  cellular neuroscience o neurons o synapse o molecule / ion channels Systems level organization  interregional system Serial and parallel organization  information flows from one area to another serially  information is organized in a parallel sense as well Hierarchical organization  top down control of functions o hierarchical relationships between neural circuitries as in the ascending striatalnigralstriatal dopamine pathways Topographical organization  topographical relationships are maintained in interconnected circuits  homunculus o topographical representation of the body in the motor cortex or somatosensory cortex Circuit organization  interregional and local circuit organization Circuit organization  same principles of circuit organization can be applied to interaction between neurons within a brain region (local) and across brain regions o six types of circuit organization patterns  A. feedforward excitation  two neurons that are connected to one another that excites a postsynaptic neuron in one direction  B. feedforward inhibition  two neurons and one interneuron are connected to one another such that activation of one neuron inhibits the activation of post synaptic neuron via the interneuron  C. convergence / divergence  neurons converge on one postsynaptic neuron  neuron diverge on multiple postsynaptic neurons  D. lateral inhibition  neuron connected to interneurons inhibits the activation of lateral or proximal postsynaptic neurons  E. feedback / recurrent inhibition  excitatory neuron connected to another excitatory neuron that in turn inhibits the previous excitatory neuron while connecting to another synapse  F. feedback / recurrent excitation  excitatory neuron connected to another excitatory neuron that in turn excites the previous excitatory neuron while connecting to another synapse Feed forward excitation / inhibition  knee jerk test o testing the normal functioning of sensory to motor connections to the spinal cord  example of feedforward excitation and inhibition  sensory neuron feeds forward back to same muscle -- exciting it  sensory neuron feeds forward to interneuron -- inhibits the muscle below it, contracting it o causes knee jerk reaction Convergence / divergence  connecting to one post synaptic neuron  connecting to many post synaptic neurons Local circuit organization in hippocampus  feedforward and feedback excitation o information flows in and feedbacks to same neuron (CA3) as well as feed forwards to another neuron (CA1)  feed forward and feedback inhibition o information flows in to one neuron (CA3) and feed forwards (excitation as well as inhibition via interneuron) to another neuron (CA1) which undergoes feedback inhibition Synaptic microcircuits  principles of convergence and divergence still apply on the synaptic level Neuron  functional and structural unit of the brain  dendrites --> soma (cell body) --> axon hillock --> axon --> terminal buttons Types of neurons  brain slice area of hippocampus CA1 o projection neuron:  larger, longer distance projections (often excitatory) o interneuron: small, locally projecting neurons (often inhibitory) Electrical activity in neurons  every neuron has a separation of electrical charge across its phospholipid cell membrane  an unequal distribution of the charges across the membrane results in a membrane potential (voltage) Equilibrium / reversal potential  balance of two forces: o electrical o chemical  E = the point at which elecctrochemical forces are qual and opposite, and there's no net flow of ions Nernst equation  forces that determine the passive distribution of ions across the membrane o concentrations of ions inside and outside cell o valence of the ion o
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