sistem saraf i.ppt

7/17/2019 SISTEM SARAF I.ppt

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Chapter 10Chapter 10

Human Anatomy & Physiology I

Overview of the Nervous SystemOverview of the Nervous System


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Organization of the Nervous SystemOrganization of the Nervous System

Peripheral nervous system - PNS

Paired Spinal and Cranial nerves

Carries messages to and from the spinal cord

and brain lins parts of the body to the CNS

Central nervous system - CNS

!rain and Spinal Cord "in dorsal body cavity#

Integration and command center interprets

sensory input and responds to input


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$Central Nervous System$brain$spinal cord

$Peripheral Nervous System$peripheral nerves

$cranial nerves$spinal nerves

Divisions of the Nervous SystemDivisions of the Nervous System


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Nervous SystemNervous System

Sensory Input monitoring stimuli occurring inside

and outside the body

Integration interpretation of sensory input

%otor utput response to stimuli by activating

effector organs

'unctions(


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Divisions Nervous SystemDivisions Nervous System


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Levels of Organization in theLevels of Organization in the

Nervous SystemNervous System


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Sensory Division

$picks up sensory information and delivers it to the CNS

Motor Division

$carries information to muscles and glands

Divisions of the Motor Division

$Somatic carries information to skeletal muscle

$Autonomic carries information to smooth muscle,cardiac muscle, and glands

Divisions of Peripheral Nervous SystemDivisions of Peripheral Nervous System


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Sensory unction$sensory receptors gather

information

$information is carried to the

CNS

!ntegrative unction

$sensory information used to

create

$sensations$memory

$thoughts

$decisions

Motor unction

$decisions are acted

upon

$impulses are

carried to effectors

Functions of Nervous SystemFunctions of Nervous System


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PNS - Two Functional DivisionsPNS - Two Functional Divisions

Sensory "afferent# )ivision

Somatic afferent nerves carry impulses from

sin* seletal muscles* and +oints to the CNS

,isceral afferent nerves transmit impulsesfrom visceral organs to the CNS

%otor "efferent# )ivision

ransmits impulses from the CNS to effector

organs* muscles and glands* to effect "bring

about# a motor response


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Sensory Neurons

$afferent$carry impulse to

CNS

$most are unipolar

$some are bipolar!nterneurons

$link neurons

$multipolar

$in CNS

Motor Neurons

$multipolar$carry impulses a"ay

from CNS

$carry impulses to

effectors

Classification of NeuronsClassification of Neurons


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Motor Division: two su!ivisionsMotor Division: two su!ivisions

Somatic Nervous System "voluntary#

Somatic motor nerve fibers "a.ons# that conduct

impulses from CNS to Seletal muscles

allo/s conscious control of seletal muscles

Autonomic Nervous System "ANS# "involuntary#

,isceral motor nerve fibers that regulate smooth

muscle* cardiac muscle* and glands

/o functional divisions sympathetic and

parasympathetic


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Levels of Organization in the Nervous SystemLevels of Organization in the Nervous System


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"istology of Nerve Tissue"istology of Nerve Tissue/o principal cell types in the nervous system(

Neurons e.citable nerve cells that transmit

electrical signals

Supporting cells cells ad+acent to neurons or

cells that surround and /rap around neurons

Cell #ypes of Neural #issue

$neurons$neuroglial cells


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Neurons #Nerve $ells%Neurons #Nerve $ells%

Highly speciali0ed* structural units of the nervous

system conduct messages "nerve impulses# from

one part of the body to another

Structure is variable* but all have a neuron cell bodyand one or more cell pro+ections called processes1

2ong life* mostly amitotic* /ith a high metabolic

rate "cannot survive more than a fe/ minutes

/ithout 3#


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&eneralize! Neuron&eneralize! Neuron


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Neuron StructureNeuron Structure


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Nerve $ell 'o!y #Peri(aryon or Soma%Nerve $ell 'o!y #Peri(aryon or Soma%

Contains the nucleus and a nucleolus

he ma+or biosynthetic center

Has no centrioles

Has /ell-developed Nissl bodies "rough

45#

A.on hilloc cone-shaped area /here

a.ons arise

Clusters of cell bodies are called Nuclei in the CNS

and 6anglia in the PNS


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ProcessesProcesses

4.tensions from the nerve cell body1 he CNScontains both neuron cell bodies and their processes1

he PNS consists mainly of neuron processes1

/o types( A.ons and )endrites

!undles of neuron processes are calledracts in the CNS and Nerves in the PNS


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Den!ritesDen!ritesShort* tapering* diffusely branched processes

he main receptive* or input regions of the neuron

"provide a large surface area for receiving signals

from other neurons#

)endrites convey incoming

messages to/ard the cell body

hese electrical signals are not

nerve impulses "not actionpotentials#* but are short distance

signals called graded potentials


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)*ons)*onsSlender processes /ith a uniform diameter arising

from the a.on hilloc* only one a.on per neuron

A long a.on is called a nerve fiber* any branches are

called a.on collaterals

erminal branches distal ends are called the a.onterminus "also synaptic nob or bouton#


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)*ons: Function)*ons: Function6enerate and transmit action potentials "nerve impulses#*

typically a/ay from the cell bodyAs impulse reaches the a.on terminals* it causes

neurotransmitters to be released from the a.on terminals

%ovement of substances along a.ons(

Anterograde - to/ard a.onal terminal "mitochondria*

cytoseletal* or membrane components#

5etrograde - a/ay from a.onal terminal "organelles forrecycling#

Anterograde 7

85etrograde


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Myelin SheathMyelin Sheath

9hitish* fatty "protein-lipoid#* segmented sheatharound most long a.ons dendrites are unmyelinated

$Protects the a.on

$4lectrically insulates fibers from one another

$Increases the speed of nerve impulse transmission


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Myelin SheathMyelin Sheath

Formed by Schwann cells in the PNS

A Sch/ann cell envelopesand encloses the a.on /ith

its plasma membrane1

he concentric layers ofmembrane /rapped

around the a.on are the

myelin sheath

Neurilemma cytoplasm

and e.posed membrane of

a Sch/ann cell


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No!es of +anvier #Neurofiral No!es%No!es of +anvier #Neurofiral No!es%

6aps in the myelin sheath bet/een ad+acent Sch/anncells

hey are the sites /here a.on collaterals can emerge


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$hite Matter

$contains myelinated

a%ons

&ray Matter

$containsunmyelinated

structures

$cell bodies, dendrites

Myelination of AxonsMyelination of Axons


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)*ons of the $NS)*ons of the $NS

!oth myelinated and unmyelinated fibers are present

%yelin sheaths are formed by oligodendrocytes

Nodes of 5anvier are more /idely spaced

here is no neurilemma "cell e.tensions are coiledaround a.ons#

9hite matter dense collections of myelinated fibers

6ray matter mostly soma and unmyelinated fibers


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'ipolar

$t"o processes$eyes, ears, nose

(nipolar

$one process$ganglia

Multipolar

$many processes$most neurons of

CNS

Classification of NeuronsClassification of Neurons


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$lassification of Neurons$lassification of Neurons

%ultipolar : three or more processes

!ipolar : t/o processes "a.on and dendrite#

;nipolar : single* short process

Structural


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Neuron $lassificationNeuron $lassification'unctional

Sensory "afferent# transmit impulses to/ard the CNS

%otor "efferent# carry impulses a/ay from the CNS

Interneurons "association neurons# lie bet/eensensory and motor path/ays and shuttle signalsthrough CNS path/ays


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Su,,orting $ells: NeurogliaSu,,orting $ells: Neuroglia

Si. types of Supporting Cells - neuroglia or glialcells < in CNS and 3 in the PNS

4ach has a specific function* but generally they(

Provide a supportive scaffold for neurons

Segregate and insulate neurons

Produce chemicals that guide young neurons

to the proper connections

Promote health and gro/th


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Sch"ann Cells$peripheral nervous

system

$myelinating cell

)ligodendrocytes

$CNS$myelinating cell

Astrocytes$CNS$scar tissue$mop up e%cess ions, etc$induce synapse formation$connect neurons to blood

vessels

Microglia$CNS$phagocytic cell

*pendyma

$CNS$ciliated

$line central canal of spinal cord$line ventricles of brain

ypes of Neuroglial Cellsypes of Neuroglial Cells


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Su,,orting $ells: NeurogliaSu,,orting $ells: Neuroglia

Neuroglia in the CNS

Astrocytes

%icroglia

4pendymal Cells

ligodendrocytes

Neuroglia in the PNS

Satellite Cells

Sch/ann Cells

utnumber neurons in the CNS by => to =* about

? the brain@s mass1


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)strocytes)strocytes%ost abundant* versatile* highly branched glial cells

Cling to neurons* synaptic endings* and cover nearbycapillaries

Support and brace neurons

Anchor neurons to nutrient

supplies

6uide migration of young neurons

Aid in synapse formation

Control the chemical environment "recapture Bions

and neurotransmitters#


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MicrogliaMicroglia

%icroglia small* ovoid cells /ith long spiny

processes that contact nearby neurons

9hen microorganisms or dead neurons are

present* they can transform into phagocytic cells


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,en!ymal $ells,en!ymal $ells

4pendymal cells range in shape from suamous to

columnar* many are ciliated

2ine the central cavities of the brain and spinal

column


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Oligo!en!rocytesOligo!en!rocytes

ligodendrocytes branched cells that line the thicer

CNS nerve fibers and /rap around them* producing an

insulating covering the %yelin sheath

S C S C


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Sch!ann Cells an" Satellite CellsSch!ann Cells an" Satellite Cells

Sch/ann cells - surround fibers of the PNS and form

insulating myelin sheaths

Satellite cells - surround neuron cell bodies /ithin

ganglia


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#egeneration of A Nerve Axon#egeneration of A Nerve Axon


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Neuro,hysiologyNeuro,hysiology

Neurons are highly irritable "responsive to stimuli#Action potentials* or nerve impulses* are(

4lectrical impulses conducted along the length

of a.ons

Al/ays the same regardless of stimulus

he underlying functional feature of the

nervous system

f


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DefinitionsDefinitions

,oltage ",# measure of potential energy bet/een

t/o points generated by a charge separation

",oltage D Potential )ifference D Potential#

Current "I# the flo/ of electrical charge

5esistance "5# tendency to oppose the current

Insulator substance /ith high electrical resistance

Conductor substance /ith lo/ electrical resistance

;nits( , "volt#* I "ampere#* 5 "ohm#

Oh . LOh . L


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Ohm.s LawOhm.s Law

he relationship bet/een voltage* current* andresistance is defined by hm@s 2a/

Current "I# +,oltage ",#

5esistance "5#

In the body* electrical current is the flo/ of ions

"rather than free electrons# across membranes

A Potential )ifference e.ists /hen there is a

difference in the numbers of B and ions on either

side of the membrane

M / $h l


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Memrane /on $hannelsMemrane /on $hannels

Passive* or leaage* channels al/ays open

Chemically "or ligand#-gated channels open

/ith binding of a specific neurotransmitter "theligand#

,oltage-gated channels open and close in

response to changes in the membrane potential

%echanically-gated channels open and close in

response to physical deformation of receptors

ypes of plasma membrane ion channels

Ligan! &ate! $hannelLigan! &ate! $hannel


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Ligan!-&ate! $hannelLigan!-&ate! $hannel

4.ample( NaB-Bgated channel

Closed /hen a neurotransmitter is not bound to thee.tracellular receptor

pen /hen a neurotransmitter is attached to the receptor -

NaB

enters the cell and B

e.its the cell

0 l & ! $h l0 lt & t ! $h l


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0oltage-&ate! $hannel0oltage-&ate! $hannel

$4.ample( NaBchannel

$Closed /hen the intracellular environment is negative

$pen /hen the intracellular environment is positive -

NaBcan enter the cell

l t h i l & !i tl t h i l & !i t


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lectrochemical &ra!ientlectrochemical &ra!ient

Ions flo/ along their chemical gradient /hen theymove from an area of high concentration to an area

of lo/ concentration

Ions flo/ along their electrical gradient /hen theymove to/ard an area of opposite charge

ogether* the electrical and chemical gradients

constitute the 424C5CH4%ICA2 65A)I4N

/ $h l/ $h l


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/on $hannels/on $hannels

9hen gated ion channels open* ions diffuse across the

membrane follo/ing their electrochemical gradients1

his movement of charge is an electrical current and

can create voltage change across the membrane1

Ion movement "flo/# along electrochemical

gradients underlies all the electrical phenomena inneurons1

,oltage ",# Current "I# . 5esistance "5#+

+ ti M P t ti l+ ti M P t ti l


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+esting Memrane Potential+esting Memrane PotentialA potential "-E>m,# e.ists across the membrane of

a resting neuron the membrane is polari0ed

# ti M $ P t ti l


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$inside is negative relative tothe outside

$polaried membrane$due to distribution of ions$Na-./-pump

#esting Mem$rane Potential#esting Mem$rane Potential

+ ti M P t ti l+ ti M P t ti l


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+esting Memrane Potential+esting Memrane Potential

Ionic differences are the conseuence of(

$)ifferent membrane permeabilities due to passive

ion channels for NaB* B*and Cl-

$peration of the sodium-potassium pump

M P t ti l Si lM P t ti l Si l


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Memrane Potentials: SignalsMemrane Potentials: Signals

%embrane potential changes are produced by(

$Changes in membrane permeability to ions$Alterations of ion concentrations across the membrane

Neurons use changes in membrane potential to

receive* integrate* and send information

/o types of signals are produced by a change in

membrane potential(

$graded potentials "short-distance#

$action potentials "long-distance#

L l f P l i tiL l f P l i ti


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Levels of PolarizationLevels of Polarization$)epolari0ation inside of the membrane becomes

less negative "or even reverses# a reduction inpotential

$5epolari0ation the membrane returns to its

resting membrane potential$Hyperpolari0ation inside of the membrane

becomes more negative than the resting potential

an increase in potential

)epolari0ation increases the probability of producing

nerve impulses1 Hyperpolari0ation reduces the

probability of producing nerve impulses1

$h i M P t ti l$h i M P t ti l


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$hanges in Memrane Potential$hanges in Memrane Potential

& ! ! P t ti l&ra!e! Potentials


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&ra!e! Potentials&ra!e! Potentials

Short-lived* local changes in membrane potential"either depolari0ations or hyperpolari0ations#

Cause currents that decreases in magnitude /ith

distanceheir magnitude varies directly /ith the strength of

the stimulus the stronger the stimulus the more the

voltage changes and the farther the current goes

Sufficiently strong graded potentials can initiate

action potentials

& ! ! P t ti l&ra!e! Potentials


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&ra!e! Potentials&ra!e! Potentials

,oltage changes in graded

potentials are decremental*the charge is uicly lost

through the permeable

plasma membrane

short- distance signal

) ti P t ti l #)P %)ction Potentials #)Ps%


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)ction Potentials #)Ps%)ction Potentials #)Ps%An action potential in the a.on of a neuron is called a

nerve impulse and is the /ay neurons communicate1

he AP is a brief reversal of membrane potential /ith

a total amplitude of =>> m, "from -E>m, to BF>m,#

APs do not decrease in strength /ith distance

he depolari0ation phase is follo/ed by a

repolari0ation phase and often a short period of

hyperpolari0ation

4vents of AP generation and transmission are the

same for seletal muscle cells and neurons

)ction Potential +esting State)ction Potential: +esting State


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NaNa++and Kand K++channels are closedchannels are closed

Each NaEach Na++channel has two voltage-regulatedchannel has two voltage-regulatedgatesgates

ctivation gates !ctivation gates !closed in the restingclosed in the resting

statestate"nactivation gates !"nactivation gates !open in the restingopen in the restingstatestate

)ction Potential: +esting State)ction Potential: +esting State

)epolari0ation opens the activation gate "rapid#

and closes the inactivation gate "slo/er# he gate

for the Bis slo/ly opened /ith depolari0ation1

De,olarization PhaseDe,olarization Phase


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De,olarization PhaseDe,olarization PhaseNaBactivation gates open uicly and NaBenters

causing local depolari0ation /hich opens moreactivation gates and cell interior becomes

progressively less negative1 5apid depolari0ation and

polarity reversal1

hreshold a critical level of depolari0ation

"-GG to -G> m,# /here

depolari0ation becomes

self-generating

Positive 'eedbac

+e,olarization Phase+e,olarization Phase


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+e,olarization Phase+e,olarization PhasePositive intracellular charge opposes further NaBentry1

Sodium inactivation gates of NaB

channels close1As sodium gates close* the slo/ voltage-sensitive B

gates open and Bleaves the cell follo/ing its

electrochemical gradient and the internal negativity ofthe neuron is restored

"y,er,olarization"y,er,olarization


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"y,er,olarization"y,er,olarization

he slo/ Bgates remain open longer than is needed

to restore the resting state1 his e.cessive efflu. causes

hyperpolari0ation of the membrane

he neuron is

insensitive tostimulus and

depolari0ation

during this time

+ole of the So!ium+ole of the So!ium


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+ole of the So!ium-+ole of the So!ium-

Potassium Pum,Potassium Pum,

5epolari0ation restores the resting electrical

conditions of the neuron* but does not restore the

resting ionic conditions

Ionic redistribution is accomplished by the

sodium-potassium pump follo/ing repolari0ation


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$at restmembrane is

polaried

$sodium

channels open

and membrane

depolaries$potassium leaves

cytoplasm and

membrane

repolaries

$threshold

stimulus reached

Potential ChangesPotential Changes

Phases of the )ction PotentialPhases of the )ction Potential


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Phases of the )ction PotentialPhases of the )ction Potential


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%mpulse Con"uction%mpulse Con"uction

A ti P t ti lA ti P t ti l


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Action PotentialsAction Potentials

Pro,agation of an )ctionPro,agation of an )ction


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Pro,agation of an )ctionPro,agation of an )ction

PotentialPotential

he action potential is self-propagating and

moves a/ay from the stimulus "point oforigin#

Stimulus /ntensityStimulus /ntensity


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Stimulus /ntensityStimulus /ntensity

Ho/ can CNS determine if a stimulus intense or

/ea

Strong stimuli can generate an action potential

more often than /eaer stimuli and the CNS

determines stimulus intensity by the freuency ofimpulse transmission

All action potentials are alie and are independent

of stimulus intensity

Threshol! an! )ction PotentialsThreshol! an! )ction Potentials


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Threshol! an! )ction PotentialsThreshol! an! )ction Potentials

hreshold ,oltage membrane is depolari0ed by =Gto 3> m,

Subthreshold stimuli produce subthreshold

depolari0ations and are not translated into APs

Stronger threshold stimuli produce depolari0ing

currents that are translated into action potentials

All-or-None phenomenon action potentials

either happen completely* or not at all

Stimulus Strength an! )PStimulus Strength an! )P


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Stimulus Strength an! )PStimulus Strength an! )P

Fre1uencyFre1uency

)solute +efractory Perio!)solute +efractory Perio!


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)solute +efractory Perio!)solute +efractory Perio!

he absolute refractory period is the time fromthe opening of the NaBactivation gates until the

closing of inactivation gates

9hen a section of membrane is generating an AP and

NaBchannels are open* the neuron cannot respond to

another stimulus

+elative +efractory Perio!+elative +efractory Perio!


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+elative +efractory Perio!+elative +efractory Perio!

he relative refractory period is the interval

follo/ing the absolute refractory period /hen(

NaBgates are closed

B

gates are open5epolari0ation is occurring

)uring this period* the threshold level is elevated*

allo/ing only strong stimuli to generate an AP

"a strong stimulus can cause more freuent AP

generation#

+efractory Perio!s+efractory Perio!s


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+efractory Perio!s+efractory Perio!s

)*on $on!uction 0elocities)*on $on!uction 0elocities


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)*on $on!uction 0elocities)*on $on!uction 0elocities

Conduction velocities vary /idely among neurons

)etermined mainly by(

A.on )iameter the larger the diameter* the faster

the impulse "less resistance#

Presence of a %yelin Sheath myelination

increases impulse speed "Continuous vs1 Saltatory

Conduction#

Saltatory $on!uctionSaltatory $on!uction


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Current passes through a myelinated a.on only at

the nodes of 5anvier

,oltage-gated NaBchannels are concentrated at

these nodes

Action potentials are triggered only at the nodes

and +ump from one node to the ne.t

%uch faster than conduction along unmyelinated

a.ons


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Saltatory Con"uctionSaltatory Con"uction



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Saltatory $on!uctionSaltatory $on!uctionCurrent passes through a myelinated a.on only at the

nodes of 5anvier "NaBchannels concentrated at nodes#

Action potentials occur only at the nodes and +ump

from node to node

Syna,seSyna,se


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Syna,seSyna,se

A +unction that mediates information transfer from

one neuron to another neuron or to an effector cell

Presynaptic neuron conducts impulses to/ard

the synapse "sender#

Postsynaptic neuron transmits impulses a/ay

from the synapse "receiver#

Ty,es of Syna,sesTy,es of Syna,ses


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Ty,es of Syna,sesTy,es of Syna,ses

A.odendritic synapse bet/een the a.on of one

neuron and the dendrite of another

A.osomatic synapse bet/een the a.on of one

neuron and the soma of another

ther types(

A.oa.onic "a.on to a.on#

)endrodendritic "dendrite to dendrite#

)endrosomatic "dendrites to soma#

Syna,sesSyna,ses


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Syna,sesSyna,ses

lectrical Syna,seslectrical Syna,ses


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lectrical Syna,seslectrical Syna,ses2ess common than chemical synapses

6ap +unctions allo/ neurons to be electricallycoupled as ions can flo/ directly from neuron to

neuron - provide a means to synchroni0e activity of

neurons

Are important in the CNS in(

Arousal from sleep

%ental attention and conscious perception4motions and memory

Ion and /ater homeostasis

Abundant in embryonic nervous tissue

$hemical Syna,ses$hemical Syna,ses


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$hemical Syna,ses$hemical Syna,ses

Speciali0ed for the release and reception of chemical

neurotransmitters

ypically composed of t/o parts(

A.on terminal of the

presynaptic neuron containing

membrane-bound synaptic

vesicles

5eceptor region on the

dendrite"s# or soma of the

postsynaptic neuron

Syna,tic $leftSyna,tic $left


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Syna,tic $leftSyna,tic $left

'luid-filled space separating the presynaptic and

postsynaptic neurons* prevents nerve impulses fromdirectly passing from one neuron to the ne.t

ransmission across the synaptic cleft(

Is a chemical event "as opposed to an electrical

one#

4nsures unidirectional communication bet/een

neurons

Syna,tic $left: /nformationSyna,tic $left: /nformation


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TransferTransfer

Nerve impulses reach the a.on terminal of the

presynaptic neuron and open Ca3Bchannels

Neurotransmitter is released into the synaptic cleft viae.ocytosis

Neurotransmitter crosses the synaptic cleft and binds

to receptors on the postsynaptic neuronPostsynaptic membrane permeability changes due to

opening of ion channels* causing an e.citatory or

inhibitory effect



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TransferTransfer

T i ti f N t itt ff tT i ti f N t itt ff t


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Termination of Neurotransmitter ffectsTermination of Neurotransmitter ffects

Neurotransmitter bound to a postsynaptic neuron

produces a continuous postsynaptic effect and also

blocs reception of additional messagesJ

erminating %echanisms(

)egradation by en0ymes

;ptae by astrocytes or the presynapticterminals

)iffusion a/ay from the synaptic cleft

Syna,tic DelaySyna,tic Delay


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Syna,tic DelaySyna,tic Delay

Neurotransmitter must be released* diffuse across

the synapse* and bind to receptors ">1F-G1> ms#

Synaptic delay is the rate-limiting step of neural

transmission

Postsyna,tic PotentialsPostsyna,tic Potentials


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Postsyna,tic PotentialsPostsyna,tic Potentials

Neurotransmitter receptors mediate graded changes

in membrane potential according to(

he amount of neurotransmitter released

he amount of time the neurotransmitter is

bound to receptors

he t/o types of postsynaptic potentials are(

4PSP e.citatory postsynaptic potentials

IPSP inhibitory postsynaptic potentials

*citatory Postsyna,tic*citatory Postsyna,tic


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*citatory Postsyna,ticc tato y ostsy a,t c

PotentialsPotentials

4PSPs are local graded depolari0ation events that

can initiate an action potential in an a.on

NaBand Bflo/ in opposite directions at the

same time

Postsynaptic membranes do not generate action

potentials1 he currents created by 4PSPs

decline /ith distance* but can spread to the a.on

hilloc and depolari0e the a.on to threshold

leading to an action potential

/nhiitory Postsyna,tic/nhiitory Postsyna,tic


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/nhiitory Postsyna,ticy y ,

PotentialsPotentials

Neurotransmitter binding to a receptor at inhibitory

synapses reduces a postsynaptic neuron@s ability to

generate an action potential

Postsynaptic membrane is hyperpolari0ed due to

increased permeability to BandKor Cl-ions1 NaB

permeability is not affected1

2eaves the charge on the inner membrane face

more negative and the neuron becomes less liely

to fireJ1

PSPs an! /PSPsPSPs an! /PSPs


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PSPs an! /PSPs

SummationSummation


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Su at o

IPSPs also summate and can summate /ith 4PSPs1

emporal Summation presynaptic neurons

transmit impulses in uic succession

Spatial Summation postsynaptic neuron is

stimulated by a large number of terminals at the

same time

A single 4PSP cannot induce an action potential

4PSPs must summate "add together# to induce an AP

SummationSummation


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NeurotransmittersNeurotransmitters


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Chemicals used for neuron communication /iththe body and the brain

%ore than G> different neurotransmitters have

been identifiedClassified chemically and functionally


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Neurotransmitters 2 $hemicalNeurotransmitters 2 $hemical


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classificationclassification$Acetylcholine "ACh#

$!iogenic amines

$Amino acids

$Peptides

$Novel messengers( AP and dissolved gases

N and C

Neurotransmitters: )cetylcholineNeurotransmitters: )cetylcholine


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#eleased at the neuromuscular $unction#eleased at the neuromuscular $unction

Enclosed in synaptic vesiclesEnclosed in synaptic vesicles

%egraded &y the acetylcholinesterase 'ChE(%egraded &y the acetylcholinesterase 'ChE(#eleased &y)#eleased &y)

! ll neurons that stimulate s*eletal musclell neurons that stimulate s*eletal muscle

! Some neurons in the autonomic nervousSome neurons in the autonomic nervoussystemsystem

yy

Neurotransmitters: 'iogenicNeurotransmitters: 'iogenic


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"nclude)"nclude)

! Catecholamines ! dopamineCatecholamines ! dopamine

norepinephrine and epinephrinenorepinephrine and epinephrine! "ndolamines ! serotonin and histamine"ndolamines ! serotonin and histamine

,roadly distri&uted in the &rain,roadly distri&uted in the &rain

lay roles in emotional &ehaviors and ourlay roles in emotional &ehaviors and our&iological cloc*&iological cloc*

gg

)mines)mines

Synthesis of $atecholaminesSynthesis of $atecholamines


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En.ymes present inEn.ymes present inthe cell determinethe cell determine

length of &iosyntheticlength of &iosynthetic

pathwaypathway

Norepinephrine andNorepinephrine anddopamine aredopamine are

synthesi.ed in a/onsynthesi.ed in a/on

terminalsterminals

Epinephrine is releasedEpinephrine is released&y the adrenal medulla&y the adrenal medulla

Neurotransmitters: )mino )ci!sNeurotransmitters: )mino )ci!s


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"nclude)"nclude)! , ! amma ', ! amma '(-amino&utyric acid(-amino&utyric acid

! lycinelycine

! spartatespartate! lutamatelutamate

ound only in the CNSound only in the CNS

Neurotransmitters: Pe,ti!esNeurotransmitters: Pe,ti!es


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"nclude)"nclude)

! Su&stance ! mediator of pain signalsSu&stance ! mediator of pain signals! ,eta endorphin dynorphin and,eta endorphin dynorphin and

en*ephalinsen*ephalins

ct as natural opiates reducing our perceptionct as natural opiates reducing our perceptionof painof pain

,ind to the same receptors as opiates and,ind to the same receptors as opiates and

morphinemorphine

ut-&rain peptides ! somatostatin andut-&rain peptides ! somatostatin and

cholecysto*inin 'produced &y non-neuralcholecysto*inin 'produced &y non-neural

tissue and widespread in " tract(tissue and widespread in " tract(

,,

Neurotransmitters: NovelNeurotransmitters: Novel


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22! "s found in &oth the CNS and NS"s found in &oth the CNS and NS! roduces e/citatory or inhi&itory responsesroduces e/citatory or inhi&itory responses

depending on receptor typedepending on receptor type! "nduces Ca"nduces Ca3+3+wave propagation in astrocyteswave propagation in astrocytes

! rovo*es pain sensationrovo*es pain sensation

MessengersMessengers

Nitric o/ide 'NO(! ctivates the intracellular receptor guanylyl

cyclase! "s involved in learning and memory

Car&on mono/ide 'CO( is a main regulator of c4 inthe &rain

Functional $lassification ofFunctional $lassification of


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2wo classifications) e/citatory and inhi&itory2wo classifications) e/citatory and inhi&itory

! E/citatory neurotransmitters causeE/citatory neurotransmitters cause

depolari.ationsdepolari.ations

'e5g5 glutamate('e5g5 glutamate(

! "nhi&itory neurotransmitters cause"nhi&itory neurotransmitters cause

hyperpolari.ations 'e5g5 , and glycine(hyperpolari.ations 'e5g5 , and glycine(


Some neurotransmitters have both e.citatory and

inhibitory effects "determined by the receptor type ofthe postsynaptic neuron#1 ACh is e.citatory at

neuromuscular +unctions /ith seletal muscle and

Inhibitory in cardiac muscle1

Neurotransmitter +ece,torNeurotransmitter +ece,tor


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%irect) neurotransmitters that open ion%irect) neurotransmitters that open ionchannelschannels! romote rapid responsesromote rapid responses

! E/amples) Ch and amino acidsE/amples) Ch and amino acids

"ndirect) neurotransmitters that act"ndirect) neurotransmitters that actthrough second messengersthrough second messengers

! romote long-lasting effectsromote long-lasting effects! E/amples) &iogenic amines peptides andE/amples) &iogenic amines peptides and

dissolved gasesdissolved gases

,

MechanismsMechanisms

$hannel-Lin(e! +ece,tors #ligan!-$hannel-Lin(e! +ece,tors #ligan!-


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gate! ion channel%gate! ion channel%

%ediate direct neurotransmitter action* action is

immediate* brief* and highly locali0ed

$2igand binds to the receptor and ions enter the cells

$4.citatory receptors depolari0e membranes

$Inhibitory receptors hyperpolari0e membranes

& Protein Lin(e! +ece,tors& Protein-Lin(e! +ece,tors


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#esponses are indirect slow comple/#esponses are indirect slow comple/

prolonged and often diffuseprolonged and often diffuse

2hese receptors are transmem&rane2hese receptors are transmem&raneprotein comple/esprotein comple/es

E/amples) muscarinic Ch receptorsE/amples) muscarinic Ch receptors

neuropeptides and those that &indneuropeptides and those that &ind

&iogenic amines&iogenic amines

& Protein-Lin(e! +ece,tors& Protein-Lin(e! +ece,tors

& Protein-Lin(e! +ece,tors:& Protein-Lin(e! +ece,tors:


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Neurotransmitter &inds to protein-lin*edNeurotransmitter &inds to protein-lin*edreceptorreceptor

protein is activated and 2 is hydroly.ed to protein is activated and 2 is hydroly.ed to

%%2he activated protein comple/ activates2he activated protein comple/ activates

adenylate cyclaseadenylate cyclase

denylate cyclase cataly.es the formation ofdenylate cyclase cataly.es the formation of

c4 from 2c4 from 2

c4 a second messenger &rings a&outc4 a second messenger &rings a&out

various cellular responsesvarious cellular responses

MechanismMechanism



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MechanismMechanism



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protein-lin*ed receptors activate intracellular protein-lin*ed receptors activate intracellular

second messengers including Casecond messengers including Ca3+3+ c4 c4

diacylglycerol as well as c4diacylglycerol as well as c4

Second messengers)Second messengers)! Open or close ion channelsOpen or close ion channels

! ctivate *inase en.ymesctivate *inase en.ymes

! hosphorylate channel proteinshosphorylate channel proteins! ctivate genes and induce proteinctivate genes and induce protein

synthesissynthesis

ffectsffects

Neural /ntegration: Neuronal PoolsNeural /ntegration: Neuronal Pools


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unctional groups of neurons that)unctional groups of neurons that)

"ntegrate incoming information received from"ntegrate incoming information received fromreceptors or other neuronal poolsreceptors or other neuronal pools

orward the processed information to its appropriateorward the processed information to its appropriate

destinationdestination

Neural /ntegration: Neuronal PoolsNeural /ntegration: Neuronal Pools

Simple neuronal pool

Input fiber presynaptic fiber

)ischarge 0one neurons most closely associated /iththe incoming fiber

'acilitated 0one neurons farther a/ay fromincoming fiber

Sim,le Neuronal PoolSim,le Neuronal Pool


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Ty,es of $ircuits in Neuronal PoolsTy,es of $ircuits in Neuronal Pools


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)ivergent one incoming fiber stimulates ever increasing number

of fibers1 hese circuits are often amplifying circuits1 "an impulsefrom a single brain neuron can activate =>> or more motor neurons

in the spinal cord and 7 =>>>s of seletal muscle fibers#

DivergenceDivergence


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$one neuron sends

impulses to several

neurons

$can amplify an

impulse$impulse from a

single neuron in

CNS may be

amplified to

activate enough

motor units needed

for muscle

contraction

Divergenceg



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Convergent opposite of

divergent circuits*

resulting in either strongstimulation or inhibition

ConvergenceConvergence


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$neuron receives input from

several neurons

$incoming impulses represent

information from differenttypes of sensory receptors

$allo"s nervous system to

collect, process, and respond

to information

$makes it possible for a

neuron to sum impulses from

different sources

gg



118/120

Ty,es of $ircuits in Neuronal Poolsy,

5everberating or oscillating chain of neuronscontaining collateral synapses /ith previous

neurons in the chain1 Involved in the control of

rhythmic activities "sleep-/ae cycle* breathing#



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y,es o $ cu s eu o a oo sy,

$Parallel after-)ischarge incoming neurons

stimulate several neurons in parallel arrays

Clinical ApplicationClinical Application


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Multiple Sclerosis

Symptoms

$blurred vision

$numb legs or arms$can lead to paralysis

Causes

$myelin destroyed in

various parts of CNS$hard scars

0scleroses1 form

$nerve impulses

blocked

$muscles do not

receive innervation

b l t d t

#reatments

$no cure$bone marro" transplant$ interferon 0anti2viral drug1

Clinical ApplicationClinical Application

sistem saraf i.ppt

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