ch39_lecture neural signaling

8/17/2019 Ch39_lecture Neural Signaling

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Copyright © 2005 Brooks/Cole — Thomson Learning

Biology, Seventh Edition Solomon • Berg • Martin

Chapter 39

Neural SignalingNeural Signaling


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Biology, Seventh Edition CHAPTER 39 Neural Signalling

• Neural signaling process• Reception of information by a

sensory receptor

• Transmission by afferent neuron tothe central nervous system

• Integration by CNS interneurons

• Efferent neuron transmission

• Action by effectors


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Stimulus response


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• Glial cells• Support and nourish neurons

• icroglia are phagocytic cells

• Astrocytes

!Some are phagocytic

!"thers help regulate composition ofthe CNS e#tracellular fluid

!ay induce and stabili$e synapses


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• "ligodendrocytes• Glial cells that form myelin

sheaths around a#ons in the CNS

• Sch%ann cells

• &orm sheaths around a#ons in

the peripheral nervous system'(NS)


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• Structure of a typical neuron• A cell body contains the nucleus

and most of the organelles

• any branched dendrites e#tend

from the cell body

• Single long a#on e#tends fromthe cell body and forms branches

called a#on collaterals


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Structure of a multipolar neuron




• *endrites receive stimuli and sendsignals to the cell body

• A#on transmits signals into its

terminal branches that end insynaptic terminals

• any a#ons are surrounded by an

insulating myelin sheath formed of

Sch%ann cells




• Nodes of Ranvier • Gaps in the sheath bet%een

successive Sch%ann cells

• Nerve• Several hundred a#ons %rapped in

connective tissue

• Ganglion

• ass of neuron cell bodies




Nerve structure




• Neuron resting potential• In a resting neuron+ the inner

surface of the plasma membrane

is negatively charged compared

%ith the outside

•(otential difference of about ,-.millivolts 'm/) across the

membrane




• *ifferences in concentrations ofspecific ions0Na1 'sodium) and

21 'potassium)0inside the cell

relative to the e#tracellular fluid• Selective permeability of the

plasma membrane to these ions

• Ions pass through specific

passive ion channels




• 21

lea3s out more readily thanNa1 can lea3 in

• Cl, 'chlorine) ions accumulate

along the inner surface of theplasma membrane

• Gradients that determine the

resting potential are maintained

by AT(




Resting potential




• Sodium,potassium pumps• Continuously transport three

sodium ions out of the neuron for

every t%o potassium ionstransported in




/oltage,activated ion channels




• *epolari$ed membrane• Stimulus caused the membrane

potential to become less negative

• 4yperpolari$ed membrane

• embrane potential becomes

more negative than the restingpotential




• Graded potential• 5ocal response that varies in

magnitude depending on the

strength of the applied stimulus

• &ades out %ithin a fe% mm of its

point of origin




• Action potential• 6ave of depolari$ation that

moves do%n the a#on

!/oltage across the membranedeclines to a critical point

!/oltage,activated ion channels

open !Na1 flo%s into the neuron

! Action potential is generated




Action potential

Bi l S h Edi i CHAPTER 39 N l Si lli




• Action potential is an all,or,none response

• No variation e#ists in the strength

of a single impulse

• embrane potential either

e#ceeds threshold level+ leadingto transmission of an action

potential+ or it does not

Bi l S th Editi CHAPTER 39 N l Si lli




• Repolari$ation• As the action potential moves

do%n the a#on+ repolari$ation

occurs behind it

• *uring depolari$ation+ the a#on

enters a refractory period !Time %hen it cannot transmitanother action potential

Bi l S th Editi CHAPTER 39 N l Si lli




Resting state *epolari$ation

Biology Seventh Edition CHAPTER 39 Neural Signalling




Repolari$ation Return to resting state



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• Continuous conduction• Ta3es place in unmyelinated

neurons

• Involves the entire a#on plasma

membrane



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• Saltatory conduction• ore rapid than continuous

conduction

• Ta3es place in myelinated

neurons

• *epolari$ation s3ips along thea#on from one node of Ranvier to

the ne#t



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Saltatory

conduction



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• Synapses• 7unction bet%een t%o neurons or

bet%een a neuron and effector

• ost synapses are chemical

• Transmission depends on release

of neurotransmitter from synapticvesicles in the synaptic terminals

of a presynaptic neuron



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• Neurotransmitters

• Acetylcholine

!Triggers contraction of s3eletal muscle

• Glutamate !ain e#citatory neurotransmitter in the

brain

• GA8A !Inhibitory neurotransmitter



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• 8iogenic amines !Norepinephrine

!Serotonin

!*opamine

!(lay important roles in regulating

mood

!*opamine is important in motor

function



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• Neuropeptides !Endorphinsm

!En3ephalins

• Nitric o#ide 'N")

!Gaseous neurotransmitter that

transmits signals from the

postsynaptic neuron to thepresynaptic neuron



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gy, g g

• Synaptic transmission

• Calcium ions cause synaptic vesicles

to fuse %ith the presynaptic

membrane and release

neurotransmitter into the synaptic

cleft

• Neurotransmitter combines %ith

specific receptors on a postsynaptic

neuron


S ti t i i


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gy, g g

Synaptic transmission



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gy g g

• Neurotransmitter receptors• any are proteins that form

ligand,gated ion channels

• "thers %or3 through a second

messenger such as cA(



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• E#citatory and inhibitory signals• E#citatory postsynaptic potential

'E(S()

!8ring the neuron closer to firing

• Inhibitory postsynaptic potential

'I(S() !ove the neuron farther a%ay fromits firing level



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• A postsynaptic neuron integratesincoming stimuli and 9decides:

%hether or not to fire

• Each E(S( or I(S( is a graded

potential

• /aries in magnitude depending onthe strength of the stimulus applied



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• The mechanism of neuralintegration is summation

• (rocess of adding and

subtracting incoming signals

• 8y summation of several E(S(s+

the neuron may be brought tocritical firing level



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• Temporal summation• Repeated stimuli cause ne%

E(S(s to develop before

previous E(S(s have decayed

• Spatial summation

• (ostsynaptic neuron stimulatedat several different places



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• Convergence• Single neuron is controlled by

converging signals from t%o or

more presynaptic neurons

• (ermits the CNS to integrate

incoming information from

various sources



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• *ivergence• Single presynaptic neuron

stimulates many postsynaptic

neurons• Allo%s %idespread effect

• Reverberation

• A#on collateral synapses %ith an

interneuron


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ch39_lecture neural signaling

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