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Chapter

PSYB65 - Communicating Within the Neuron: The Action Potential

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Department
Psychology
Course
PSYB65H3
Professor
Ted Petit
Semester
Fall

Description
Communication Within the Neuron The Action PotentialWhen a neurotransmiiter diffuses across the synapse to interact w postsynaptic site a series of electrical events can occur some send information and some inhibit informationThe electrical events that make the transmissioninhibition of information relies on the balance of ions between the inside of the neuron intracellular and the outside of the neuron extracellularWhen the neuron is at rest it maintains an electrical charge 70 mV which means that the electrical charge on the inside of the neurons is 70 Mv lessthan the charge on the outsidethis is calledresting potentialThe RP of the neuron depends on the difference between the concentration of ions across the neuron membraneneurons contain variety of ions most important are Na ions and K ionsAt rest extracellular fluid contains high concentration of Na and intracellular fluid contains high concentration of KIn the brain ions are concentrated in either extracellularintracellular fluidThe neuron has 2 properties that promote the uneven distribution of ions 1 Related to permeability of the cell membrane that covers the neuronmembrane is not permeable to all types of ions y Ion cross the membrane through proteins embedded din the membrane called ion channels y At rest K crosses the membrane where Na cant However given enough time enough Na would sneak into the cell and enough K would leak out of the neuron that there would be homogeneous distributions of the ions y Neurons actively import K and actively transport Na through transport mechanism called sodiumpotassium pump requires neuron to use energy EXCHANGES 3 Na IONS ON THE INSUDEE AND 2 K IONS ON THE OUTSIDE y When neurotransmitter diffuses across synapse it can open ion channels that allow rapid influxinflow of Na into the neuron and rapid efflux outside flow of K from the neurony Opening of Na channels makes intracellular space morey The change in membrane potential of 70 mV to 50 mV is called depolarization also an action potential occurs neurotransmitters are relapsed from terminal buttonsy As a neuron becomes polarized K channels open and K ions rapidly leave the neuron The efflux triggers closing of Na channels and the neuron returns back to RP called repolarization y Bc Kchannels take longer to close some additional K leak out causing temporary change in membrane 70mV called hyperpolarizationThere are several features of an AP that must be considered 1 There are times when action potential cant be triggered ie when neuron is strongly depolarized Na channels close and cant be reopened The inability to open channels results in period of time during which an AO cant be triggered called the absolute refractory period 2 The myelination of axonsmost are not uniformly located on the axon there are a number of small gaps in the myelin called the nodes of Ranvier y In myelinated neurons ion channels and NaK pumps occur ONLY at the node of RanvierWhen an AP first reaches the axons its passively propagated to the first node of Ranvier which results in production of a new AP at the node of Ranvier This depolarization bumps to the next and the sequence of events occurs again y The jumping of AP from 1 node of Ranvier o another is called salutatory conduction and occurs down the entire length of the axon y Each node generates a new AP resulting in an AP that is uniform size Communication Between Neurons The SynapsesWI the neuron communication is largely electrical However between neurons it is chemicalAlthough most synapses are axodendritic consists of axons that form synapses with dendritic spines there are other types of synapses 1 Axoxomatic syanpses are axons forming synapses with somacell bodies of other neurons 2 Axoaxonic synapses are axons forming synapses with other axonsThe terminal button of the axon contains 12s of small packagesvesicles that contain neurotransmitters located next to active zones areas of protein accumulation on membrane that allow vesicle to deposit its contents into the synapseRelease is triggered by AP at terminal button of axon AP causes Ca 2 channels to open and rushes into the neuronAn increase in concentration of Ca causes neurotransmitter to be released into synapse through exocytosis membranes of vesicle fuse w axonal membrane at the active zone which results in opening in vesiclepore allowing neurotransmitter to flow into the synapseOnce of neurotransmitter is released it diffuses across the synapse to produce postsynaptic effects occurs when neurotransmitter binds to protein embedded in postsynaptic membranereceptor
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