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BIO271H1 2014 MIDTERM NOTES - section 1 (Lectures 1-6).pdf

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University of Toronto St. George
Christopher Garside

Lecture 1 Organization of the Nervous SystemCNSbrain and spinal cordPNSnerves innovating tissues of the bodyHippocampus responsible for episodic memory can still learn long term things unconscious about itmany cells have a voltage difference across their cell membranes termed the membrane potentialdifference of voltage on outside and inside of the cellExcitable cells can rapidly change their membrane potential in response to an incoming signal neuron is one type of excitable cellrapidly change membrane potential ex by generating APNeurons are excitable cells that can transmit electrical signals over long distancesPurkinje cells output neurons of cerebellum coordinates motorhas dendritic arbor tree Action potential how neurons transmit information to long distances Neurons and Gliaregardless of what a neuron looks like they all have similar zonesas a result in general neurons are polarized information goes in one directionneurons vary in structure and properties but use the same basic mechanisms to send signalsmotor neurons innervates musclessensory neurons neurons that bring information from the peripheralskin on handbrings information to the nervous systemPurkinje Cell cerebellum Cell body of motor and Purkinje cell is closer to the dendrites sensory neuron cell bodies are in another placeRegardless of what the neurons look like they all have these 4 important zoneszones show you the pathway of how information is going to flow through the neuron how electrical information is going to flowinformation flow is in one directionreceive information decide what to do with it and transmit itneuron is polarized information goes from one region to anotherDendrites receive information sensory part of neuronforms synapses with other incoming cells from many synaptic inputs within a short period of timeas much as 1000 inputssecondSignal integration zone decides where ALL of these signals go a large enough amount will generate an action potentialthe action potential generated convey information down axon and at the end of the axon it will cause the presynaptic terminals to release neurotransmitters neuron can then communicatenot all inputs or inhibition of APSignal integration zoneaxon hillock where AP Is generated on axon hillockend of the cell bodyaxon hillock The axon hillock is a specialized part of the cell body or soma of a neuron that connects to the axon As a result the axon hillock is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axonGlial cells are also important in the nervous systemNeural Zones Four Functional Zones 1 Signal Receptiono Dendrites and cell body soma receives inputs o These incoming signal received and converted to change in membrane potential 2 Signal Integration o Axon hillockwhere the axon comes off of cell bodyalso called the signal integration zone where action potential is generated o Strong signal is converted to an action potential AP o Decides what to do with inputs happens at axon hillockgenerate action potential or not o Axon hillockspike initiation zone region where youre most likely to generate an action potentialwhere an action potentialspike is generated in this signal integration zone 3 Signal Conduction o Axon some wrapped in myelin sheathhelps propagate signal effectively and quicklydisease Multiple Sclerosisdegradation of myelin sheathsdont have the proper conduction o Action potential travels down axon 4 Signal Transmission o Axon terminals o Release of neurotransmitters o Release of neurotransmitter releases a signal that is sent to next cell which will be received by dendrites and this process repeats v As a result of this organization neurons have a specific polarity information comes in and travels down a particular pathIf All these Neurons Look Different How Can We Define ThemDendrites are not just simple processescovered in small protrusions knobsSpick initiation zone region most likely to generate an APNeural ZonesNeurons communicate directly with OTHER cell types as wellwhen neuron innervates muscleall of our motor movements is caused by our neurons innovating our musclescalled the Neuromuscular Junction NMJTo differentiate between an axon and dendrite you need a fluorescent label of an antibody Somacell body responsible for metabolic maintenance of cellNerve processesaxondendritesDendrites extend from soma are branched receive signals from other neurons and carry them to the somaNeurons with extensive dendritic branching are often referred to as neurons with a dendritic arbor or treeAxons conduct signals away from the soma can be very long metersCarry information with high fidelity and without loss of signal strengthAxons terminate into axon terminals allowing the neuron to communicate with other tissuesDendrites receive and integrate the info sometimes the soma also receives info directlyAction potentials APs are then generated in the spikeinitiation zone located near the axon hillockAPspikenerve impulseAPs travel down the axon to the terminals where they cause neurotransmitter releaseDendritic Spinesdendrites are actually covered with small protrusions called spinesProtrusions exists on most dendrites in CNSspines are sites of postsynaptic regionMajority of information inputs are on the spines which comes off on main shaft of dendritesSpines are structures on dendritesPostsynaptic sitesdendritic spinesOn the signal reception zone dendritic arborin each dendritic branch there are a LOT of dendritic spines covered with spinesClicker in which neural zone does a change in membrane potential initiate action potential A signal receptionreceives input but does not generate an AP B signal integrationconverts inputs to AP or no AP C signal conduction D signal transmissionElectrical Signals in Neuronsneurons have a resting membrane potential like all cells o membrane potential is negative at rest o membrane potential electrical difference between the inside and outside of the cell o in neurons it is approximately 70mVneurons are excitable o can rapidly change their membrane potentialdepolarization membrane potential becomes less negativerepolarization membrane potential returns to resting valuehyperpolarization membrane potential becomes more negative than resting value At First Membrane Potential was Determine Experimentally2 electrodes one on inside and one on outsideRelative Difference Electrode outside the cell is 0 the recorded value inside of the cell is the membrane potential difference between inside and outside of the cellInside of the cell is more negatively charged than the outside and the value is about 70mV 70mV difference between the inside and outside of the cellNeuron has to use energy to maintain 70mvso why do they want to keep this membrane potential Allows neuron to store a bit of energy which can then be used to generate an electrical signalwhen cell wants to transmit a signal it can generate an AP ex From 70mV to50mVVERY rapid changewhen this happens the cell is excitatory Membrane potential at rest is polarized 70 more negative in the cellChange membrane potentialchange how polarized it is o 70mV0mVless polarizedat 0mV there is no difference inside and outside the celldepolarization o 70mV90mVmore polarizedhyperpolarization o if we depolarize and hyperpolarize then we return back to resting membrane potential we are repolarizingChanges in Membrane PotentialNeurons have a resting membrane potential like all cellsMembrane potential is negative at restNeurons are excitable o Can rapidly change their membrane potentialDepolarizationmembrane potential becomes less negativeRepolarizationmembrane potential returns to 1 First put electrode in 70mV is recorded resting value resting membrane potentialHyperpolarizationmembrane potential becomes 2 Potential changesgets closer to 0more negative than resting value depolarizationless polarizedChanges in membrane potential act as electrical signals 3 Slowly gets back to 70mVrestingPositive charges coming into the celldepolarization making membrane potential againrepolarized it less negative 4 Then slowly pass to 90mVNegative charges coming into the cellhyperpolarization of hyperpolarization membrane 5 Then drop back to 70mV These changes in polarization are electricalsignals that neuron uses as informationsource Membrane Potential factors contributing to membrane potential o distribution of ions across the membrane o relative permeability of the ions
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