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    Nerve Physiology

    Gian Carlo Delante, PhB PTRP RPT

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    Basic Types of Neurons

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    Parts of a Neuron

    Dendrites

    Cell Body (soma)

    Axon hillock

    Axon

    yelin sheath

    !ch"ann cells

    Nodes of #anvier Collaterals

    Axon terminals

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    $lial Cells

    A%A& Neuroglia

    !upport cells of the 'rain

    aintains delicate internal environment

    of the CN! Astrocytes& help CN! neurons form the

    'lood'rain 'arrier that protects the CN!from harmful chemicals

    Microglia& protects neurons from 'acteria

    Oligodendrocytes(CN!) Schwann cells(PN!)

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    Sequence of !ents at aChe"ical Syna#se

    *+ Presyna#tic neuronssynthesi-e neurotrans"ittersthat arestored in syna#tic !esicles+

    .+ An action potential in the presynaptic neuron depolari-es themem'rane and activates !oltage$gated Ca%%channels'Ca//(the

    "hite molecules in the animation) 0o" into the axon terminal+ 1+ Ca//cause the synaptic vesicles to fuse to the "all of the synaptic

    terminal2 causing e(ocytosisand the release of neurotransmitter+

    3+ Neurotransmitter di4uses across the cleft and acts on che"icalrece#torsfound on the #ostsyna#tic cellmem'rane+

    5+ #eceptors cause the opening of che"ically gated ion channels+ 6+ The postsynaptic mem'rane potential changes2 causing

    a de#olari)ationor hy#er#olari)ationdepending on the type ofneurotransmitter+ (A depolari-ation increasesthe pro'a'ility of anaction potential on the postsynaptic neuron2 "hile a

    hyperpolari-ation decreasesthe likelihood)

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    7on Channels

    8oltagegated 7on Channels

    Allo" ions to pass through in response tochanges in electrical membrane potential

    Axon hillock2 axon2 axon terminals

    9igandgated 7on Channels

    Allo" ions to pass through in response to the'inding of a chemical messenger (ligand)such as a neurotrans"itter

    Dendrites2 cell 'ody

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    9igands

    A%A& Neurotransmitters

    (citatory 7n0ux of positive ions or e:ux of negative ions

    em'rane more #ositi!e $lutamate

    Acetylcholine (ACh)

    *nhi+itory

    7n0ux of negative ions or e:ux of positive ions em'rane more negati!e

    $ABA

    $lycine

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    Postsynaptic Potentials(P!P)

    (citatory Postsyna#tic PotentialsPSP- Produced 'y excitatory neurotransmitters (ligands)

    Di"inishesas it travels along dendrite and cell'ody

    must 'e strong enoughto spread all the "ayfrom the synapse "here it originated to the axonhillock

    *nhi+itory Postsyna#tic Potentials *PSP- Produced 'y inhi'itory neurotransmitters (ligands)

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    Threshold Potential

    The "ini"u"potential of a mem'rane that"hen reached can trigger an action potential

    Achieved 'y the su""ationof excitatory

    potentials (;P!P

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    Action Potential versus

    !ynaptic Potential

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    !patial and Temporal !ummation of!ynaptic Potentials

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    Action Potential

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    #efractory Periods

    A+solute#efractory Period the interval during "hich a second

    action potential a'solutely cannot'e

    initiated2 no matter ho" large a stimulusis applied

    Relati!e#efractory Period

    the interval immediately follo"ingduring "hich initiation of a secondaction potential is inhibited'ut notimpossi'le

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    Propagation of the Action PotentialDo"n an @nmyelinated Nerve

    *+ here an action potential exists on the axon2 the insideof the mem'rane is positive (a'out /15 m8) "ith respectto the outside 'ecause of the Na/that have entered thecell+

    .+ This positive charge is attracted to and moves to"ardan area of the mem'rane next to it that is at rest and hasa negative charge this creates a local current (/ )+

    1+ Because of this 'uildup of the positive charge2 theadacent area of the mem'rane no" depolari-es+

    3+ This depolari-ation triggers voltagegated Na/channelsto open+

    5+ Na/2rushes into the cell and depolari-es the region tothreshold2 creating a ne" action potential+

    6+ By a repetition of this procedure2 the action potential is

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    Propagation of the Action Potential Do"n a yelinatedNerve&

    Saltatory Conduction

    *+ The positive charge from the existing actionpotential is attracted to and moves to"ard theadacent node of #anvier that is negative+

    .+ This node of #anvier no" depolari-es+ 1+ This depolari-ation triggers voltagegated

    Na/channels to open+

    3+ Na/rushes into the cell and depolari-es the

    region to threshold2 and a ne" action potential isgenerated+

    5+ By a repetition of this procedure2 the actionpotential is propagated along the mem'rane+

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    All or Nothing Principle

    of Action Potentials

    if threshold is notreached2 thenatural repolari-ing forces of themem'rane "ill return the mem'rane

    potential to normal (E m8)

    Fnce threshold is reached2 you "illgenerate an action potential and this

    action potential "ill 'e propagateddo"n the axon at its full heightwithoutdecreasing in si-eG

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    ;P!P

    hat ions "ill move during an

    ;P!PH

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    7P!P

    hat ions "ill move during an

    7P!PH

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    IBattleJ of P!P

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    #evie"


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