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© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
Chapter 28 Nervous Systems
Introduction
Spinal cord injuries disrupt communication between
– the central nervous system (brain and spinal cord) and
– the rest of the body.
© 2012 Pearson Education, Inc.
Over 250,000 Americans are living with spinal cord
injuries.
Spinal cord injuries
– happen more often to men,
– happen mostly to people in their teens and 20s,
– are caused by vehicle accidents, gunshots, and falls, and
– are usually permanent because the spinal cord cannot be
repaired.
Introduction
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28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
The nervous system
– obtains sensory information, sensory input,
– processes sensory information, integration, and
– sends commands to effector cells (muscles) that carry out
appropriate responses, motor output.
© 2012 Pearson Education, Inc.
Figure 28.1A
Sensory receptor
Effector cells
Sensory input
Motor output
Integration
Brain and spinal cord
Central nervous
system (CNS)
Peripheral nervous
system (PNS)
The central nervous system (CNS) consists of the
– brain and
– spinal cord (vertebrates).
The peripheral nervous system (PNS)
– is located outside the CNS and
– consists of
– nerves (bundles of neurons wrapped in connective tissue) and
– ganglia (clusters of neuron cell bodies).
28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
© 2012 Pearson Education, Inc.
Sensory neurons
– convey signals from sensory receptors
– to the CNS.
Interneurons
– are located entirely in the CNS,
– integrate information, and
– send it to motor neurons.
Motor neurons convey signals to effector cells.
28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
© 2012 Pearson Education, Inc.
Figure 28.1B
Sensory receptor
2 1
3
4
Sensory neuron
Brain
Spinal cord
Interneuron
CNS PNS
Nerve Flexor muscles
Quadriceps muscles
Ganglion
Motor neuron
28.2 Neurons are the functional units of nervous systems
Neurons are
– cells specialized for carrying signals and
– the functional units of the nervous system.
A neuron consists of
– a cell body and
– two types of extensions (fibers) that conduct signals,
– dendrites and
– axons.
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Myelin sheaths
– enclose axons,
– form a cellular insulation, and
– speed up signal transmission.
28.2 Neurons are the functional units of nervous systems
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Figure 28.2
Signal direction
Nucleus
Myelin
sheath Schwann
cell
Dendrites Cell
body Axon
Nodes of
Ranvier
Signal
pathway
Node of Ranvier
Synaptic
terminals
Nucleus Schwann
cell
Cell body
Layers of
myelin
Figure 28.2_1
Signal direction
Nucleus
Myelin
sheath Schwann
cell
Dendrites Cell
body Axon
Nodes of
Ranvier
Signal
pathway
Synaptic
terminals
Figure 28.2_2
Node of Ranvier
Layers of
myelin
Nucleus Schwann
cell
NERVE SIGNALS
AND THEIR TRANSMISSION
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28.3 Nerve function depends on charge differences across neuron membranes
At rest, a neuron’s plasma membrane has potential
energy—the membrane potential, in which
– just inside the cell is slightly negative and
– just outside the cell is slightly positive.
The resting potential is the voltage across the
plasma membrane of a resting neuron.
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The resting potential exists because of differences in
ion concentration of the fluids inside and outside the
neuron.
– Inside the neuron
– K+ is high and
– Na+ is low.
– Outside the neuron
– K+ is low and
– Na+ is high.
28.3 Nerve function depends on charge differences across neuron membranes
© 2012 Pearson Education, Inc.
Animation: Resting Potential
Figure 28.3
Neuron Axon
Plasma membrane
Plasma
membrane
Na channel
Outside of neuron
K channel
Inside of neuron
Na
Na
Na
Na
Na
K K
K
K K
K
K
K
K
K
K
Na Na
Na
Na Na
Na Na Na
Na
Na Na
Na Na
Na K
K K K K
Na-K
pump
ATP
K
Figure 28.3_1
Neuron Axon
Plasma membrane
Figure 28.3_2
Plasma
membrane
Na channel
Outside of neuron
K channel
Inside of neuron
Na
Na
Na
Na
Na
K K
K
K
K
K
K K
K
Na Na
Na
Na
Na
Na
Na
Na
Na
Na Na
K
K
K
K
Na-K
pump ATP
K K K
Na
Na
Na
K
28.4 A nerve signal begins as a change in the membrane potential
A stimulus is any factor that causes a nerve signal
to be generated. A stimulus
– alters the permeability of a portion of the membrane,
– allows ions to pass through, and
– changes the membrane’s voltage.
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A nerve signal, called an action potential, is
– a change in the membrane voltage,
– from the resting potential,
– to a maximum level, and
– back to the resting potential.
28.4 A nerve signal begins as a change in the membrane potential
© 2012 Pearson Education, Inc.
Animation: Action Potential
Figure 28.4
Na Na
K
Additional Na channels
open, K channels are
closed; interior of cell
becomes more positive.
Na Na
2
K
A stimulus opens some Na
channels; if threshold is reached,
an action potential is triggered.
Na Na
K
1 Resting state: Voltage-gated Na
and K channels are closed;
resting potential is maintained by
ungated channels (not shown).
Sodium
channel
Potassium
channel Outside
of neuron
Plasma membrane
Inside of neuron
Action
potential
Threshold
Resting potential
Time (msec)
Mem
bra
ne p
ote
nti
al
(mV
)
50
0
50
100
2
3
1
3 4
5 1
Na Na
K
4 Na channels close
and inactivate; K
channels open, and
K rushes out;
interior of cell is more
negative than outside.
Na Na
K
The K channels
close relatively
slowly, causing a
brief undershoot.
5
1 Return to resting
state.
Figure 28.4_s1
Action
potential
Threshold
Resting potential
Time (msec)
Me
mb
ran
e p
ote
nti
al
(mV
)
50
0
50
100
1
Resting state: Voltage-
gated Na and K
channels are closed;
resting potential is
maintained by ungated
channels (not shown).
1
Na Na
K
Sodium
channel Outside
of neuron
Plasma membrane
Inside of neuron
Potassium
channel
Figure 28.4_s2
Action
potential
Threshold
Resting potential
Time (msec)
Me
mb
ran
e p
ote
nti
al
(mV
)
50
0
50
100
1
2
Na A stimulus opens some Na
channels; if threshold is reached,
an action potential is triggered.
Na
K
2
Figure 28.4_s3
Action
potential
Threshold
Resting potential
Time (msec)
Me
mb
ran
e p
ote
nti
al
(mV
)
50
0
50
100
1
2
3
3 Na Na
K
Additional Na channels
open, K channels are
closed; interior of cell
becomes more positive.
Figure 28.4_s4
Na
K
Na channels close
and inactivate; K
channels open, and
K rushes out;
interior of cell is more
negative than outside.
Na
Action
potential
Threshold
Resting potential
Time (msec)
Me
mb
ran
e p
ote
nti
al
(mV
)
50
0
50
100
1
2
3 4
4
Figure 28.4_s5
Action
potential
Threshold
Resting potential
Time (msec)
Me
mb
ran
e p
ote
nti
al
(mV
)
50
0
50
100
1
2
3 4
5
5 The K channels
close relatively
slowly, causing a
brief undershoot.
Figure 28.4_s6
Action
potential
Threshold
Resting potential
Time (msec)
Me
mb
ran
e p
ote
nti
al
(mV
)
50
0
50
100
1
2
3 4
5 1
1 Na Na
K
Return to resting
state.
28.5 The action potential propagates itself along the axon
Action potentials are
– self-propagated in a one-way chain reaction along a
neuron and
– all-or-none events.
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Figure 28.5_s1
Plasma
membrane
Axon
segment
Action
potential Na
1
Na
Figure 28.5_s2
Na
1
Na
Na
Na
K
K
Action potential
2
Plasma
membrane
Axon
segment
Action
potential
Figure 28.5_s3
Na
1
Na
Na
Na
K
K
Action potential
2
Plasma
membrane
Axon
segment
Action
potential
Action potential
Na
K
K 3
Na
Figure 28.5
Axon
Plasma
membrane
Axon
segment
Action
potential Na
Na
Na
Action potential
Na
Na
Action potential
K
K
K
K
Na
1
2
3
The frequency of action potentials (but not their
strength) changes with the strength of the stimulus.
28.5 The action potential propagates itself along the axon
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28.6 Neurons communicate at synapses
Synapses are junctions where signals are
transmitted between
– two neurons or
– between neurons and effector cells.
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Electrical signals pass between cells at electrical
synapses.
At chemical synapses
– the ending (presynaptic) cell secretes a chemical signal, a
neurotransmitter,
– the neurotransmitter crosses the synaptic cleft, and
– the neurotransmitter binds to a specific receptor on the
surface of the receiving (postsynaptic) cell.
28.6 Neurons communicate at synapses
© 2012 Pearson Education, Inc.
Animation: Synapse
Figure 28.6
Axon of
sending
cell
Synaptic
terminal
of sending
cell
Dendrite
of receiving
cell
Sending cell
Synaptic
vesicles
Synaptic
terminal
Synaptic
cleft
Vesicle fuses
with plasma
membrane
Action
potential
arrives
Neurotransmitter
is released into
synaptic cleft
Neurotransmitter
binds to receptor Neurotransmitter
molecules
Neurotransmitter broken
down and released
Ion channel closes
Ions
Receptor
Receiving
cell
Neurotransmitter
Ion channels
Ion channel opens 5 6
4
3 2
1
Figure 28.6_1
Axon of
sending
cell
Synaptic
terminal
of sending
cell
Dendrite
of receiving
cell
Sending cell
Synaptic
vesicles
Synaptic
terminal
Synaptic
cleft
Vesicle fuses
with plasma
membrane
Action
potential
arrives
Neurotransmitter
is released into
synaptic cleft
Neurotransmitter
molecules
Receiving
cell Ion channels
Neurotransmitter
binds to receptor
1
2 3
4
Figure 28.6_2
Neurotransmitter broken
down and released
Ion channel closes
Neurotransmitter
Ion channel opens
Ions
Receptor
6 5