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Nerve Cells

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Physiology 1021
John Ciriello

2nd Week Modules May1111 803 PM Module 4 Nerve Cells Nerve CellNeuronNerve cells and muscles are considered EXCITABLE they can use the resting membrane potential yto generate an electrochemical impulse called and ACTION POTENTIAL considered to be the language of the NS because this is the way nerve cells communicate with one another AP are also necessary for muscle contraction y Structure of a Nerve CellDendrite hairlike structures at the end of a neuron that receive incoming signalscommunicate with other neuronsCell BodySoma control centre of the cell contains the nucleus And all necessary organelles for directing cellular activity y Axon Hillock point at which the action potential begins its generation in the cell specialized region from where axon projectsAxon projection of cell body used to carry signals to the target cell in the form of a action potentialphospholipids bilayer insulator sheath Made up of myelinated area called the myelin sheathyand Node of Ranvier where ionic channels that make the action potential take place maymay not be myelinatedy Collaterals branching of axon near terminal end serve to increaseof possible target cells with which a neuron can interactTerminal BoutonAxon Terminal swelling at the end of axon collateral containing mitochondriamembranebound vesicles containing various neurochrine moleculesChemicals in axon terminal facilitate transmission of the signal across the synapse to target cell y Action Potential The AP is a rapid reversal of the resting membrane yDuring this event inside cell the membrane potential rapidly changes from resting 70mV to yroughly 35mVThis sudden change to a more positiveis called DEPOLARIZATION yAfter this phase the membrane potential rapidly returns to 70mV called REPOLARIZATION yThe membrane potential briefly becomes more negative reaching roughly 90mV this is called yHYPERPOLARIZATION After this negative phase the membrane potential returns to the resting levels of 70mVy VoltageGated Channels Voltagegated sodiumvoltagegated potassium channels yIn the neuron these channels are generally found on the axonand are essential for the ygeneration of a APThese channels are sensitive to changes in membrane potentialsOPEN when the inside of the ycell becomes more VoltageGated Sodium ChannelsOnly allows Na through yGates open only when their is a depolarizationy Summary of events 1 Depolarization of the membrane occurs becomes more 2 Activation gate opens immediately3 Na flows into the cell DOWN the concentration gradient 4 Inactivation gate CLOSES and Na can NO longer flow into the cellthe channel CANNOT open 5 Channel returns to resting configuration inactivation opens and activation gate closes 6 Channel is now ready to open again
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