Types of neuronesTypes of neurones
Histological ClassificationHistological Classification
1- Unipolar.1- Unipolar.
2- Bipolar2- Bipolar
3- Multipolar3- Multipolar
Functional classificationFunctional classification ::
1- Sensory ( afferent )1- Sensory ( afferent ) :: conductconduct
impulses from receptors to C.N.S .impulses from receptors to C.N.S .
2- Motor (efferent):2- Motor (efferent): conductconduct
impulses from the C.N.S to theimpulses from the C.N.S to the
effector organ.effector organ.
3-Interneurons3-Interneurons:: are located insideare located inside
the C.N.S connect each other &the C.N.S connect each other &
connect sensory & motor neurons.connect sensory & motor neurons.
Structure of neuroneStructure of neurone
Cell body ( soma )Cell body ( soma ) ::
The soma also contains :The soma also contains :
Nissil bodiesNissil bodies :: responsiple for proteinresponsiple for protein
NeurofibrilsNeurofibrils :: extend into cell processes &extend into cell processes &
form the main support of the neuron.form the main support of the neuron.
Microtubules & MicrofilamentsMicrotubules & Microfilaments :: theythey
extend into the axon & have supportive andextend into the axon & have supportive and
transport function ( axoplasmic transporttransport function ( axoplasmic transport ).).
NO centrosomeNO centrosome
2- Cell processes:2- Cell processes:
a-Dendrites :a-Dendrites :
- Multiple short processes- Multiple short processes
extend from the cell body .extend from the cell body .
- Collect impulses & transmit- Collect impulses & transmit
them towards the cell body.them towards the cell body.
b- Axonb- Axon ::
-- Single long process that conductSingle long process that conduct
impulses away from the cell body.impulses away from the cell body.
- Vary in length from few millimeter to- Vary in length from few millimeter to
about one meter .about one meter .
- Its origin from the cell body is called- Its origin from the cell body is called
the axon hillock .the axon hillock .
- It branches freely near its terminal .- It branches freely near its terminal .
- The terminal branches end by swollen- The terminal branches end by swollen
part (synaptic knobs) which containpart (synaptic knobs) which contain
chemical transmitter vesicles .chemical transmitter vesicles .
Types of axonsTypes of axons
Axons are one of two types :Axons are one of two types :
covered by myelin sheath&covered by myelin sheath&
neurilemmal sheath.neurilemmal sheath.
covered only by neurilemmal sheathcovered only by neurilemmal sheath
but no underlined myelin sheath .but no underlined myelin sheath .
Myelin sheathMyelin sheath
lipoprotein in nature & insulatorlipoprotein in nature & insulator
formed in peripheral nervousformed in peripheral nervous
system by wrapping of cellsystem by wrapping of cell
membrane ofmembrane of Schwan cellsSchwan cells
around the axon while in thearound the axon while in the
C.N.S. it is formed byC.N.S. it is formed by
oligodendroglial cellsoligodendroglial cells ..
absent from axon hillock &absent from axon hillock &
terminal branches .terminal branches .
interrupted at intervals ofinterrupted at intervals of
about 0.1 – 1.0 mm by nodesabout 0.1 – 1.0 mm by nodes
of Ranvierof Ranvier
responsiple for the whiteresponsiple for the white
colour of myelinated nerve&colour of myelinated nerve&
the white matter of C.N.S .the white matter of C.N.S .
Resting membrane potentialResting membrane potential
( R.M.P.)( R.M.P.)
DefinitionDefinition:: It is theIt is the
potential difference betweenpotential difference between
inside & outside theinside & outside the
membrane at restmembrane at rest
ValueValue :: it is – 70 mv.it is – 70 mv.
it is measured by specialit is measured by special
apparatus withapparatus with
microelectrodes , amplifier ,andmicroelectrodes , amplifier ,and
sensitive voltmeter .sensitive voltmeter .
One microelectrode is put inOne microelectrode is put in
the inner side of the membranethe inner side of the membrane
& the other microelectrode is& the other microelectrode is
put on the outside surface .put on the outside surface .
Causes of RMPCauses of RMP
1- Selective1- Selective
permeability of thepermeability of the
2- Sodium – potassium2- Sodium – potassium
1-Selective permeability of the1-Selective permeability of the
POTASSIUM ION DIFFUSIONPOTASSIUM ION DIFFUSION ::
The cell membrane is about 100The cell membrane is about 100
times more permeable fortimes more permeable for
potassium ions than for sodiumpotassium ions than for sodium
Potassium ions are concentratedPotassium ions are concentrated
inside 30-40 times more thaninside 30-40 times more than
Potassium ions tend to movePotassium ions tend to move
from inside the cell to outside.from inside the cell to outside.
Potassium ion diffusionPotassium ion diffusion
continue untill the positivecontinue untill the positive
charge outside the membranecharge outside the membrane
reach a level that repells thereach a level that repells the
outflow of more potassium ionsoutflow of more potassium ions
(( equilibrium ofequilibrium of potassium ionpotassium ion
diffusiondiffusion ) .) .
SODIUM ION DIFFUSIONSODIUM ION DIFFUSION ::
Sodium ion concentration outsideSodium ion concentration outside
the membrane is 10-15 times thethe membrane is 10-15 times the
concentration inside.concentration inside.
Sodium tends to diffuse to insideSodium tends to diffuse to inside
the cell.the cell.
Sodium ion diffusion is limited bySodium ion diffusion is limited by
the low permeability of the restingthe low permeability of the resting
membrane to sodium.membrane to sodium.
CHLORIDE ION DIFFUSION :CHLORIDE ION DIFFUSION :
Chloride ions tend to diffuse fromChloride ions tend to diffuse from
outside to inside the celloutside to inside the cell
(concentrated 25 times outside more(concentrated 25 times outside more
than inside ) .than inside ) .
This diffusion is prevented byThis diffusion is prevented by
repulsionrepulsion force caused by theforce caused by the
negativitynegativity insideinside & also by the& also by the
attractionattraction force between chloride &force between chloride &
sodium ionssodium ions outsideoutside the membrane .the membrane .
PROTEIN DIFFUSIONPROTEIN DIFFUSION ::
The cell membrane offersThe cell membrane offers
absolute barrier to the passageabsolute barrier to the passage
of organic anions (proteins),of organic anions (proteins),
because the protein moleculesbecause the protein molecules
are of large size .are of large size .
They cannot pass through theThey cannot pass through the
cell membrane.cell membrane.
movement of ions at rest occurmovement of ions at rest occur
through thethrough the leak proteinleak protein
channelschannels which are alwayswhich are always
the most important ion at restthe most important ion at rest
is the potassiumis the potassium ion because ofion because of
highest concentration gradienthighest concentration gradient
& highest membrane& highest membrane
Function of sodium-potassiumFunction of sodium-potassium
1- It1- It keepskeeps highhigh Na + concentrationNa + concentration outsideoutside
the cell & highthe cell & high K+ concentrationK+ concentration inside theinside the
cell .cell .
2- It is an2- It is an electrogenic pump.Itelectrogenic pump.It pumps threepumps three
positive charges to outside & only twopositive charges to outside & only two
positive charges to inside with the result ofpositive charges to inside with the result of
one negative charge inside , helpone negative charge inside , help
negativity of R.M.P.negativity of R.M.P.
3-3- keeps normal cell volumekeeps normal cell volume by preventingby preventing
accumulation of electrolytes inside the cellaccumulation of electrolytes inside the cell
Action potentialAction potential
DefinitionDefinition :: it is theit is the rapidrapid
propagatedpropagated change in membranechange in membrane
potential as a result ofpotential as a result of stimulationstimulation
by an effective stimulusby an effective stimulus
MONOPHASIC ACTIONMONOPHASIC ACTION
ItIt is recorded by putting oneis recorded by putting one
microelectrode in the inside surfacemicroelectrode in the inside surface
of the membrane & the other on theof the membrane & the other on the
outer surface.outer surface.
Monophasic action potentialMonophasic action potential
Latent periodLatent period
it is theit is the timetime passed sincepassed since
application of stimulus until theapplication of stimulus until the
start of recording action potential.start of recording action potential.
It depends on theIt depends on the velocity ofvelocity of
conductionconduction in the nerve & thein the nerve & the
distance between the stimulatingdistance between the stimulating
and the recording electrode .and the recording electrode .
It is inversely proportional to theIt is inversely proportional to the
velocity of conduction but directlyvelocity of conduction but directly
proportional to the distanceproportional to the distance
between the stimulating &between the stimulating &
recording electrode .It can be usedrecording electrode .It can be used
to calculate the velocity ofto calculate the velocity of
conduction as follows :conduction as follows :
Velocity =Velocity =
Distance / Latent period.Distance / Latent period.
Na + & K + conductance
during Action potential
Spike potential :Spike potential :
It is composed of two limbs :It is composed of two limbs :
a-a-ascending limbascending limb
( Depolarization wave ) .( Depolarization wave ) .
b-b-descending limbdescending limb
( Repolarization wave).( Repolarization wave).
Duration of the spike potential isDuration of the spike potential is
0.5 – 1.0 m.sec0.5 – 1.0 m.sec
Sodium channels during action
The ascending limbThe ascending limb
( Depolarization ):( Depolarization ):
--It is due to Na+ influx & it is of two phases:It is due to Na+ influx & it is of two phases:
a-Slow phase :a-Slow phase : from R.M.P. till firing levelfrom R.M.P. till firing level
( from –70 mv to –55 mv ) it is due to( from –70 mv to –55 mv ) it is due to
increase in Na+ permeability by the effectincrease in Na+ permeability by the effect
of the stimulusof the stimulus
b-Rapid phase :b-Rapid phase : from –55 mv to + 35 mvfrom –55 mv to + 35 mv
It is due to rapid Na+ influx caused byIt is due to rapid Na+ influx caused by
opening of Na+ voltage gated channels .opening of Na+ voltage gated channels .
The descending limbThe descending limb
( repolarization ) :( repolarization ) :
It represents the major part of theIt represents the major part of the
process of repolarization (about 70process of repolarization (about 70
It is due to closure of Na+ voltageIt is due to closure of Na+ voltage
gated channels & opening of K+gated channels & opening of K+
voltage gated channels resulting involtage gated channels resulting in
rapid k+ efflux while Na+ influxrapid k+ efflux while Na+ influx
Voltage gated Na+ & K+Voltage gated Na+ & K+
channels open by the samechannels open by the same
signal ( change of membranesignal ( change of membrane
potential from resting state to –potential from resting state to –
55 mv ).55 mv ).
Na+ voltage gated channelsNa+ voltage gated channels
are rapid to open & rapid toare rapid to open & rapid to
close while K+ voltage gatedclose while K+ voltage gated
channels are slow .channels are slow .
Depolarazation triggers Phases
Gate open rapidly
To stop cycle
aa-After depolarization :-After depolarization :
( Negative after potential )( Negative after potential )
durationduration 4 m.sec.4 m.sec.
it is theit is the slow repolarizationslow repolarization
following the descending limb offollowing the descending limb of
the spike till R.M.P. is reachedthe spike till R.M.P. is reached
it is due toit is due to slow K+ outfluxslow K+ outflux due todue to
closure of some voltage gated K+closure of some voltage gated K+
channels. .channels. .
b-b-After hyperpolarizationAfter hyperpolarization ::
( Positive after potenial )( Positive after potenial )
durationduration 40 m.sec.40 m.sec.
it isit is small hyperpolarizationsmall hyperpolarization followingfollowing
the after depolarization till the R.M.P.the after depolarization till the R.M.P.
is reached .is reached .
it is caused by :it is caused by :
a- some K+ voltage gated channels stilla- some K+ voltage gated channels still
b- increased activity of Na+ - K+ pump.b- increased activity of Na+ - K+ pump.
This is anThis is an active processactive process that needsthat needs
energy .energy .
TheThe depolarized point make a potentialdepolarized point make a potential
difference with the adjacent point.difference with the adjacent point.
A current develop between that point &A current develop between that point &
the adjacent pointthe adjacent point which becomewhich become
depolarized to the firing level producing adepolarized to the firing level producing a
new action potential in the new point.new action potential in the new point.
The new action potential producesThe new action potential produces
another action potential at the adjacentanother action potential at the adjacent
point & so on.point & so on.
Differences between propagation inDifferences between propagation in
myelinated & unmyelinated nerve fibers :myelinated & unmyelinated nerve fibers :
nerve fibersnerve fibers
nerve fibersnerve fibers
Type ofType of
( jumping )( jumping )
Point to pointPoint to point
Velocity ofVelocity of
Consume lessConsume less
Consume moreConsume more
Biphasic action potentialBiphasic action potential
It is measured by putting theIt is measured by putting the twotwo
microelectrodesmicroelectrodes on theon the outer surface.outer surface.
As the depolarization wave reaches theAs the depolarization wave reaches the
electrode near the stimulator , theelectrode near the stimulator , the
electrode becomes negative relative to theelectrode becomes negative relative to the
other electrode & a downward deflection isother electrode & a downward deflection is
recorded .recorded .
When the wave passes to the part of theWhen the wave passes to the part of the
nerve fiber between the two electrodes ,nerve fiber between the two electrodes ,
the potential difference returns to zero .the potential difference returns to zero .
When the wave reaches the secondWhen the wave reaches the second
electrode , it becomes negativeelectrode , it becomes negative
relative to the first electrode & anrelative to the first electrode & an
upward deflection is recorded .upward deflection is recorded .
When the depolarization wave leavesWhen the depolarization wave leaves
the second electrode , the potentialthe second electrode , the potential
difference returns again to zero.difference returns again to zero.
Therefore , the record shows aTherefore , the record shows a
downward deflection followed by andownward deflection followed by an
isoelectric interval & then an upwardisoelectric interval & then an upward
Biphasic action potential
In the nearby
In the distant
It is the ability of nerveIt is the ability of nerve
fiber or muscle fiber tofiber or muscle fiber to
respond to stimuli .respond to stimuli .
Stimulus :Stimulus :
It is the change in the surroundingIt is the change in the surrounding
environment .environment .
Types of stimuli :Types of stimuli :
1-1- ElectricalElectrical :: it is of two types :it is of two types :
a-Galvanica-Galvanic :: direct current obtaineddirect current obtained
from a battery of low intensity & offrom a battery of low intensity & of
long duration.long duration.
b-Farradicb-Farradic :: high intensity & of shorthigh intensity & of short
duration .duration .
Electrical stimuli are commonlyElectrical stimuli are commonly
used in experimental workused in experimental work
because they are :because they are :
1- easily applied .1- easily applied .
2- accurately adjusted as strength &2- accurately adjusted as strength &
duration .duration .
3- similar to physiological process of3- similar to physiological process of
4- cause no or minimal damage to the4- cause no or minimal damage to the
3-3- PhysicalPhysical ::
a-a-ThermalThermal :: cooling & warmingcooling & warming
b-b-MechanicalMechanical : stretch , touch: stretch , touch
& pressure .& pressure .
c-c-ElectromagneticElectromagnetic :: lightlight
stimuli to the retina of the eye.stimuli to the retina of the eye.
Factors affectingFactors affecting
effectiveness of stimuli :effectiveness of stimuli :
1-Strength (intensity) of1-Strength (intensity) of
2- Duration (time of2- Duration (time of
application) of stimuli.application) of stimuli.
3- Rate of rise of intensity.3- Rate of rise of intensity.
1-Strength (intensity) of stimuli1-Strength (intensity) of stimuli ::
According to the stimulus strength theAccording to the stimulus strength the
following types of stimuli are known :following types of stimuli are known :
Sub minimal stimulusSub minimal stimulus (sub(sub
threshold):threshold): it produces no actionit produces no action
potential ,but only produces localizedpotential ,but only produces localized
change (local excitatory state)change (local excitatory state)
Minimal (threshold ) stimulusMinimal (threshold ) stimulus :: it is theit is the
weakest stimulus which can produce anweakest stimulus which can produce an
action potential.action potential.
Supra threshold stimulusSupra threshold stimulus ..
Maximal stimulus.Maximal stimulus.
Supramaximal stimulus.Supramaximal stimulus.
Threshold ,supra threshold ,Threshold ,supra threshold ,
maximal & supra maximalmaximal & supra maximal
stimuli produce the same actionstimuli produce the same action
potential in single nerve fiberpotential in single nerve fiber
because it obeys the all or nonbecause it obeys the all or non
2-Duration (the time of application)2-Duration (the time of application)
of stimulus :of stimulus :
The duration of stimulus is closelyThe duration of stimulus is closely
related to the strength.related to the strength.
The strength-duration curve can beThe strength-duration curve can be
obtained by stimulating the nerve withobtained by stimulating the nerve with
electrical stimuli of different intensitieselectrical stimuli of different intensities
and recording the time needed byand recording the time needed by
each stimulus to start the response.each stimulus to start the response.
From the curve we observe thatFrom the curve we observe that
1-Within limits1-Within limits , the stronger the, the stronger the
stimulus , the shorter will be the duration .stimulus , the shorter will be the duration .
22-There is a-There is a minimal timeminimal time , less than this, less than this
time , no stimulus whatever its strengthtime , no stimulus whatever its strength
can produce response .can produce response .
33-There is a-There is a minimal strengthminimal strength
((Rheobase)Rheobase) , less than this strength , no, less than this strength , no
stimulus whatever its duration canstimulus whatever its duration can
produce response .produce response .
4-The4-The ChronaxieChronaxie is the timeis the time
needed by stimulus strengthneeded by stimulus strength
double rheobase to producedouble rheobase to produce
N.B. :N.B. :
It is aIt is a measuremeasure of excitability .of excitability .
It isIt is inversily proportionalinversily proportional toto
excitability .excitability .
3- Rate of rise of intensity3- Rate of rise of intensity ::
The stimulus becomes effectiveThe stimulus becomes effective
only if the rate of riseonly if the rate of rise exceeds aexceeds a
certain limit.certain limit.
When the current rises too slowly,When the current rises too slowly,
thethe nerve accommodatesnerve accommodates itself toitself to
the rise of the current (thethe rise of the current (the
threshold of stimulation isthreshold of stimulation is
Excitability changesExcitability changes
during an action potentialduring an action potential
During conduction of a nerveDuring conduction of a nerve
impulse , the excitability of the nerveimpulse , the excitability of the nerve
fibers varies & it passes in thefibers varies & it passes in the
following phases:following phases:
1-Temporal rise of excitability1-Temporal rise of excitability ::
it is associated with the localit is associated with the local
response (local depolarization ) in theresponse (local depolarization ) in the
nerve fiber before the firing level .nerve fiber before the firing level .
Excitability changes duringExcitability changes during
1- Initial increase.
2- Absolute refractory period
3- Relative refractory period
4- Super-normal phase.
5- Subnormal phase
Absolute refractory period (A.R.P):Absolute refractory period (A.R.P):
it corresponds to the ascending limb & theit corresponds to the ascending limb & the
first third of the descending limb of thefirst third of the descending limb of the
spike potential .The excitability isspike potential .The excitability is
completely lost = zero ( no stimuluscompletely lost = zero ( no stimulus
whatever its strength can excite ) .whatever its strength can excite ) .
Significance :Significance : A.R.P. limits the numberA.R.P. limits the number
of impulses that can be produced &of impulses that can be produced &
conducted by the nerve fibersconducted by the nerve fibers
Mechanism :Mechanism :
During the ascending limb theDuring the ascending limb the
Na+ voltage gated channels areNa+ voltage gated channels are
already opened ( no effect ofalready opened ( no effect of
other stimuli).other stimuli).
During the first third ofDuring the first third of
descending limb Na+ channelsdescending limb Na+ channels
are closed by the inactivationare closed by the inactivation
gate and can not be opened.gate and can not be opened.
Relative refractory periodRelative refractory period
( R.R.P. ):( R.R.P. ):
It corresponds to the second two thirds ofIt corresponds to the second two thirds of
the descending limb of spike potential .the descending limb of spike potential .
The excitability is less than normal (supraThe excitability is less than normal (supra
threshold stimulus strength can excite).threshold stimulus strength can excite).
MechanismMechanism :: it is due to difficulty to openit is due to difficulty to open
the closed voltage gated Na+ channels .the closed voltage gated Na+ channels .
4- Supernormal phase:4- Supernormal phase:
it corresponds to the afterit corresponds to the after
depolarization ( the membrane isdepolarization ( the membrane is
partially depolarized) .partially depolarized) .
The excitability is higher thanThe excitability is higher than
(sub threshold stimulus can(sub threshold stimulus can
5-5- Subnormal phase :Subnormal phase :
It corresponds to the after hyperIt corresponds to the after hyper
polarization .polarization .
The excitability is lower thanThe excitability is lower than
Supra threshold stimuli areSupra threshold stimuli are
needed to excite .needed to excite .
Factors affectingFactors affecting
excitability of nerve fibersexcitability of nerve fibers
1- Physical factors1- Physical factors
2- Chemical factors2- Chemical factors
3- Electrical factors3- Electrical factors
1- Physical factors1- Physical factors
Warming increase excitability due toWarming increase excitability due to
increase of the metabolic reactions .increase of the metabolic reactions .
Cooling decrease excitability due toCooling decrease excitability due to
decrease of the metabolic reactions .decrease of the metabolic reactions .
MechanicalMechanical :: deep pressuredeep pressure
decrease excitabilitydecrease excitability
2- Chemical factors2- Chemical factors ::
A- Local anaestheticsA- Local anaesthetics ::
Local anaesthetics asLocal anaesthetics as
cocaine , novocaine &cocaine , novocaine &
xylocaine decreasexylocaine decrease
excitability by decreasing Na+excitability by decreasing Na+
permeability .permeability .
B- Ions :B- Ions :
-- Calcium :Calcium :
Increase E.C.F calcium decreasesIncrease E.C.F calcium decreases
excitability by decreasing Na+excitability by decreasing Na+
permeability & decrease E.C.F. calciumpermeability & decrease E.C.F. calcium
do the reverse.do the reverse.
- Sodium:- Sodium:
Increase E.C.F. sodium increaseIncrease E.C.F. sodium increase
excitability while its decrease decreasesexcitability while its decrease decreases
Potassium :Potassium :
increase of E.C.F. potassiumincrease of E.C.F. potassium
increase excitability while itsincrease excitability while its
decrease decreases excitability .decrease decreases excitability .
Oxygen lack & carbon dioxideOxygen lack & carbon dioxide
excess:excess: decreases excitability .decreases excitability .
Acidosis:Acidosis: decreases excitabilitydecreases excitability
whilewhile alkalosisalkalosis increases it.increases it.
3-Electrical factors3-Electrical factors
( Electrotonus ) :( Electrotonus ) :
These are the changes that occurThese are the changes that occur
at the cathode (catelectrotonus) &at the cathode (catelectrotonus) &
at the anode (anelectrotonus)at the anode (anelectrotonus)
when a subthreshold galvanicwhen a subthreshold galvanic
current is applied to a nerve fiber .current is applied to a nerve fiber .
CatelectrotonusCatelectrotonus :: slightslight
depolarizationdepolarization occurs near theoccurs near the
cathodecathode which is accompaniedwhich is accompanied
byby increased excitabilityincreased excitability ..
AnelectrotonusAnelectrotonus :: slightslight hyperhyper
polarizationpolarization occurs near theoccurs near the
anodeanode which is accompaniedwhich is accompanied
byby decreased excitabilitydecreased excitability..
Types of nerve fibersTypes of nerve fibers
TypeType AA BB CC
DiameterDiameter 3-20 um3-20 um 1-3 um1-3 um 0.5-1.0 um0.5-1.0 um
MyelinationMyelination MyelinatedMyelinated MyelinatedMyelinated unmyelinatedunmyelinated
Velocity ofVelocity of
10-120 m/sec10-120 m/sec 5-10 m/sec5-10 m/sec 0.5-5.0 m/sec0.5-5.0 m/sec
Sensitivity toSensitivity to
+ + + ++ + + +
+ ++ +
+ ++ +
+ + + ++ + + +
ExampleExample Sensory &Sensory &
motor somaticmotor somatic
All or non lawAll or non law
Action potential either occursAction potential either occurs
maximally or it does not occurmaximally or it does not occur
at all , provided that all otherat all , provided that all other
conditions remain constant .conditions remain constant .
It is obeyed by a single nerveIt is obeyed by a single nerve
or single muscle fiber .or single muscle fiber .
Sub minimal ( sub threshold )Sub minimal ( sub threshold )
stimulus does not produce anstimulus does not produce an
action potential .action potential .
Threshold stimulus producesThreshold stimulus produces
the maximal action potential .the maximal action potential .
Supra threshold , maximal &Supra threshold , maximal &
supra maximal stimuli producesupra maximal stimuli produce
the same action potential .the same action potential .
Differences between action potentialDifferences between action potential
& local excitatory state& local excitatory state
excitatory stateexcitatory state
CauseCause Sub thresholdSub threshold
Threshold & more.Threshold & more.
All or non lawAll or non law Doesn’t obey.Doesn’t obey. Obeys.Obeys.
GradationGradation Can be graded.Can be graded. No gradation.No gradation.
SummationSummation Can be summated.Can be summated. No summation.No summation.
ConductionConduction Decreased graduallyDecreased gradually
till disappear.till disappear.
Conducted with theConducted with the
same intensity.same intensity.
Action potential in mixed nerveAction potential in mixed nerve
(compound action potential)(compound action potential)
Mixed nerve contains different types ofMixed nerve contains different types of
nerve fibers withnerve fibers with differentdifferent excitabilityexcitability &&
differentdifferent velocity of conductionvelocity of conduction ..
Action potential in mixed nerve:Action potential in mixed nerve:
1- Has multiple peaks1- Has multiple peaks :: the first peak isthe first peak is
caused by the most rapid fibers followedcaused by the most rapid fibers followed
by the peak of less rapid fibers & lastly theby the peak of less rapid fibers & lastly the
peak of the slowest fibers.peak of the slowest fibers.
2- Doesn't obey all or non law2- Doesn't obey all or non law ::
Sub threshold stimulusSub threshold stimulus produces no actionproduces no action
potential .potential .
Threshold stimulusThreshold stimulus produces an actionproduces an action
Supra thresholdSupra threshold stimulus produces morestimulus produces more
intense action potentialintense action potential
Maximal stimulusMaximal stimulus produces the maximalproduces the maximal
action potential due to stimulation of all nerveaction potential due to stimulation of all nerve
fibers .fibers .
Supra maximal stimulusSupra maximal stimulus produces the sameproduces the same
maximal action potentiamaximal action potentia
Action potential in a mixed nerveAction potential in a mixed nerve
(Compound action potential)(Compound action potential)