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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"