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8/17/2019 Ch39_lecture Neural Signaling
1/41
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition Solomon • Berg • Martin
Chapter 39
Neural SignalingNeural Signaling
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Copyright © 2005 Brooks/Cole — Thomson Learning
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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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Stimulus response
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 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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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• "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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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 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
8/17/2019 Ch39_lecture Neural Signaling
7/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Structure of a multipolar neuron
8/17/2019 Ch39_lecture Neural Signaling
8/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• *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
8/17/2019 Ch39_lecture Neural Signaling
9/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 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
8/17/2019 Ch39_lecture Neural Signaling
10/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Nerve structure
8/17/2019 Ch39_lecture Neural Signaling
11/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 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
8/17/2019 Ch39_lecture Neural Signaling
12/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• *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
8/17/2019 Ch39_lecture Neural Signaling
13/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 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(
8/17/2019 Ch39_lecture Neural Signaling
14/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Resting potential
8/17/2019 Ch39_lecture Neural Signaling
15/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Sodium,potassium pumps• Continuously transport three
sodium ions out of the neuron for
every t%o potassium ionstransported in
8/17/2019 Ch39_lecture Neural Signaling
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Biology, Seventh Edition CHAPTER 39 Neural Signalling
/oltage,activated ion channels
8/17/2019 Ch39_lecture Neural Signaling
17/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• *epolari$ed membrane• Stimulus caused the membrane
potential to become less negative
• 4yperpolari$ed membrane
• embrane potential becomes
more negative than the restingpotential
8/17/2019 Ch39_lecture Neural Signaling
18/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Graded potential• 5ocal response that varies in
magnitude depending on the
strength of the applied stimulus
• &ades out %ithin a fe% mm of its
point of origin
8/17/2019 Ch39_lecture Neural Signaling
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Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Action potential• 6ave of depolari$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
8/17/2019 Ch39_lecture Neural Signaling
20/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Action potential
Bi l S h Edi i CHAPTER 39 N l Si lli
8/17/2019 Ch39_lecture Neural Signaling
21/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 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
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22/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Repolari$ation• As the action potential moves
do%n the a#on+ repolari$ation
occurs behind it
• *uring depolari$ation+ the a#on
enters a refractory period !Time %hen it cannot transmitanother action potential
Bi l S th Editi CHAPTER 39 N l Si lli
8/17/2019 Ch39_lecture Neural Signaling
23/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Resting state *epolari$ation
Biology Seventh Edition CHAPTER 39 Neural Signalling
8/17/2019 Ch39_lecture Neural Signaling
24/41Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Repolari$ation Return to resting state
Biology Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Continuous conduction• Ta3es place in unmyelinated
neurons
• Involves the entire a#on plasma
membrane
Biology Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Saltatory conduction• ore rapid than continuous
conduction
• Ta3es place in myelinated
neurons
• *epolari$ation s3ips along thea#on from one node of Ranvier to
the ne#t
Biology Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
Saltatory
conduction
Biology Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 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
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Neurotransmitters
• Acetylcholine
!Triggers contraction of s3eletal muscle
• Glutamate !ain e#citatory neurotransmitter in the
brain
• GA8A !Inhibitory neurotransmitter
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• 8iogenic amines !Norepinephrine
!Serotonin
!*opamine
!(lay important roles in regulating
mood
!*opamine is important in motor
function
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition CHAPTER 39 Neural Signalling
• Neuropeptides !Endorphinsm
!En3ephalins
• Nitric o#ide 'N")
!Gaseous neurotransmitter that
transmits signals from the
postsynaptic neuron to thepresynaptic neuron
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
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
Biology, Seventh Edition CHAPTER 39 Neural Signalling
S ti t i i
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Copyright © 2005 Brooks/Cole — Thomson Learning
gy, g g
Synaptic transmission
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
gy g g
• Neurotransmitter receptors• any are proteins that form
ligand,gated ion channels
• "thers %or3 through a second
messenger such as cA(
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
• 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
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
• 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
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
• 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
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
• 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
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
• 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
Biology, Seventh Edition CHAPTER 39 Neural Signalling
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Copyright © 2005 Brooks/Cole — Thomson Learning
• *ivergence• Single presynaptic neuron
stimulates many postsynaptic
neurons• Allo%s %idespread effect
• Reverberation
• A#on collateral synapses %ith an
interneuron
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