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Neuron organization and structure
 Cell Body
 Neurotransmitter
 Axon
 Synapse
 Dendrites
Dendrites
 Glia (glial cells)
Axon
hillock
Nucleus
Cell
body
Presynaptic
cell
Axon
Synaptic
terminals
Synapse
Neurotransmitter
Synaptic
terminals
Postsynaptic cell
Figure 48.3
Introduction to Information Processing
 Sensory neurons
 Interneurons
80 µm
Glia
Cell bodies of neurons
 Motor neurons
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Figure 48.4
 Central nervous system
Siphon
Sensory input
Integration
Sensor
 Peripheral nervous system
Motor output
Proboscis
Processing center
 nerves
Effector
Figure 48.5
Cell
body
Dendrites
Ion pumps and ion channels – resting potential
Axon
 membrane potential
Sensory neuron
 resting potential
Interneuron
Motor neuron
Formation of the Resting Potential
Table 48.1
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Figure 48.6
 Ion channels
Key
Na+
K+
OUTSIDE OF CELL
Sodiumpotassium
pump
Potassium
channel
Sodium
channel
INSIDE OF CELL
Modeling the Resting Potential
 In a resting neuron, the currents of K+ and Na+ are
equal and opposite, and the resting potential
across the membrane remains steady
Action potentials
Hyperpolarization
 gated ion channels
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(a) Graded hyperpolarizations
produced by two stimuli
that increase membrane
permeability to K+
Figure 48.9
Ions
Stimulus
+50
Membrane potential (mV)
Change in
membrane
potential
(voltage)
Ion
channel
Gate closed: No ions
flow across membrane.
Gate open: Ions flow
through channel.
−50
−100
(b) Graded depolarizations
produced by two stimuli
that increase membrane
permeability to Na+
Threshold
Resting
potential
Hyperpolarizations
0 1 2 3 4 5
Time (msec)
Stimulus
+50
Membrane potential (mV)
Depolarization
0
0
−50
Threshold
Resting
potential
Depolarizations
−100
(c) Action potential
triggered by a
depolarization that
reaches the threshold
Strong depolarizing stimulus
+50
Membrane potential (mV)
Graded Potentials and Action Potentials
0 1 2 3 4 5
Time (msec)
Action
potential
0
−50
Threshold
Resting
potential
−100
0 1 2 3 4 5 6
Time (msec)
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Key
Generation of Action Potentials
Na+
K+
 At resting potential
3 Rising phase of the
action potential
4 Falling phase of the
action potential
+50
Membrane potential
(mV)
1.
2.
Action
potential
2
−50
2 Depolarization
OUTSIDE OF CELL
3.
−100
Sodium
channel
3
0
4
Threshold
1
5
1
Resting potential
Time
Potassium
channel
INSIDE OF CELL
Inactivation loop
5 Undershoot
1 Resting state
Generation of Action Potentials
 At resting potential
 Refractory period
4.
5.
Conduction of Action Potentials
Figure 48.12
Axon
Plasma
membrane
Action
potential
Cytosol
Na+
K+
Action
potential
Na+
K+
K+
Action
potential
Na+
K+
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Node of Ranvier
Evolutionary Adaptations of Axon Structure
Layers of myelin
Axon
 myelin sheath
 oligodendrocytes
Schwann
cell
Axon
Myelin sheath
Schwann
cell
Nucleus of
Schwann cell
Nodes of
Ranvier
0.1 µm
 Schwann cells
Figure 48.14
 Nodes of Ranvier
Schwann cell
Depolarized region
(node of Ranvier)
Myelin
sheath
Cell body
 saltatory conduction
Axon
Neurons communicate with other cells at
synapses
Figure 48.16
Presynaptic cell
1
Axon
Postsynaptic cell
Synaptic vesicle
containing neurotransmitter
Synaptic
cleft
Postsynaptic
membrane
Presynaptic
membrane
3
K+
4
Ca2+ 2
Voltage-gated
Ca2+ channel
Ligand-gated
ion channels
Na+
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Generation of Postsynaptic Potentials
 ligand-gated ion channels
 Postsynaptic potentials fall into two categories
 Excitatory postsynaptic potentials (EPSPs
 Inhibitory postsynaptic potentials (IPSPs)
Figure 48.17
Terminal branch
of presynaptic
neuron
E1
E1
Membrane potential (mV)
E2
Postsynaptic
neuron
I
E1
E1
E2
E2
0
Neurotransmitters
Axon
hillock
I
Threshold of axon of
postsynaptic neuron
E2
I
Action
potential
I
Action
potential
Resting
potential
−70
E1
E1 + E2
E1 E1
E1
(a) Subthreshold, no
summation
(b) Temporal summation
E1
(c) Spatial summation
I
E1 + I
(d) Spatial summation
of EPSP and IPSP
PRESYNAPTIC NEURON
Acetylcholine
Neurotransmitter
Neurotransmitter
receptor
Inactivating enzyme
POSTSYNAPTIC NEURON
(a) Enzymatic breakdown of neurotransmitter in the
synaptic cleft
Neurotransmitter
Neurotransmitter
receptor
Neurotransmitter
transport
channel
(b) Reuptake of neurotransmitter by presynaptic neuron
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Table 48.2a
Table 48.2b
Table 48.2c
Amino Acids
 Amino acid neurotransmitters are active in the
CNS and PNS
 Known to function in the CNS are
 Glutamate
 Gamma-aminobutyric acid (GABA)
 Glycine
Biogenic Amines
 Biogenic amines include
 Epinephrine
 Norepinephrine
 Dopamine
 Serotonin
 They are active in the CNS and PNS
Neuropeptides
 Several neuropeptides, relatively short chains of
amino acids, also function as neurotransmitters
 Neuropeptides include substance P and
endorphins, which both affect our perception of
pain
 Opiates bind to the same receptors as endorphins
and can be used as painkillers
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Gases
Figure 48.UN01b
 Gases such as nitric oxide (NO) and carbon
monoxide (CO) are local regulators in the PNS
 Unlike most neurotransmitters, NO is not stored in
cytoplasmic vesicles, but is synthesized on
demand
 It is broken down within a few seconds of
production
Opiate
Lowest Concentration That
Blocked Naloxone Binding
Morphine
Yes
6 × 10−9 M
Methadone
Yes
Levorphanol
Phenobarbital
Yes
No
Atropine
No
2 × 10−8 M
2 × 10−9 M
No effect at 10−4 M
No effect at 10−4 M
Serotonin
No
No effect at 10−4 M
Drug
 Although inhaling CO can be deadly, the
vertebrate body synthesizes small amounts of it,
some of which is used as a neurotransmitter
Figure 48.UN03
Action potential
Membrane potential (mV)
+50
Falling
phase
0
Rising
phase
Threshold (−55)
−50
Resting
potential
−70
−100
Depolarization
Undershoot
0 1 2 3 4 5 6
Time (msec)
9