Download Chapter 28 Nervous Systems

Chapter 28
Nervous Systems
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Introduction
 Spinal cord injuries disrupt communication between
– the central nervous system (brain and spinal cord) and
– the rest of the body.
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Introduction
 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.
© 2012 Pearson Education, Inc.
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 input
Integration
Sensory receptor
Motor output
Brain and spinal cord
Effector cells
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
28.1 Nervous systems receive sensory input,
interpret it, and send out appropriate
commands
 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).
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28.1 Nervous systems receive sensory input,
interpret it, and send out appropriate
commands
 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.
© 2012 Pearson Education, Inc.
Figure 28.1B
1
Sensory
receptor
2
Sensory
neuron
Brain
Ganglion
Motor
neuron
Spinal
cord
3
Quadriceps
muscles
4
Interneuron
Nerve
Flexor
muscles
PNS
CNS
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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28.2 Neurons are the functional units of nervous
systems
 Myelin sheaths
– enclose axons,
– form a cellular insulation, and
– speed up signal transmission.
© 2012 Pearson Education, Inc.
Figure 28.2
Signal direction
Cell body
Nucleus
Signal
pathway
Node of Ranvier
Layers of
myelin
Nodes of
Ranvier
Myelin
sheath
Dendrites
Cell
body
Schwann
cell
Synaptic
terminals
Nucleus
Axon
Schwann
cell
Figure 28.2_1
Signal direction
Nucleus
Nodes of
Ranvier
Myelin
sheath
Dendrites
Cell
body
Schwann
cell
Axon
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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28.3 Nerve function depends on charge differences
across neuron membranes
 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.
Animation: Resting Potential
© 2012 Pearson Education, Inc.
Figure 28.3
Neuron
Axon
Plasma
membrane
Outside of neuron
Na
Na
Na
Na
K
K
Na
channel
Na
Plasma
membrane
Na
Na
Na
K
Na
Na
Na
Na
Na-K
pump
K
K
Na
Na
Na
Na
ATP
K channel
K
Na
K
K
Na
Na
K
K
Inside of neuron
K
K
K
K
K
K
K
Figure 28.3_1
Neuron
Plasma
membrane
Axon
Figure 28.3_2
Outside of neuron
Na
Na
Na
Na
K
K
Na
Na
Na
Na
K
Na
Na
Na
Na
Na
Na
Na
Na
channel
Plasma
membrane
K
Na-K
pump
K
Na
ATP
K channel
K
Na
K
K
Na
Na
K
K
Inside of neuron
K
K
K
K
K
K
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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28.4 A nerve signal begins as a change in the
membrane potential
 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.
Animation: Action Potential
© 2012 Pearson Education, Inc.
Figure 28.4
Na
Na
Na
Na
K
Additional Na channels
open, K channels are
closed; interior of cell
becomes more positive.
Na
Na
K
2
K
50
Membrane potential
(mV)
3
Action
potential
3
0
5
The K channels
close relatively
slowly, causing a
brief undershoot.
4
50 Threshold
1
Resting potential
100
5
1
Time (msec)
Sodium Potassium
Na channel channel
Na channels close
and inactivate; K
channels open, and
K rushes out;
interior of cell is more
negative than outside.
2
A stimulus opens some Na
channels; if threshold is reached,
an action potential is triggered.
Na
4
Outside
of neuron
Na
Na
Plasma membrane
K
1
K
Inside of neuron
Resting state: Voltage-gated Na
and K channels are closed;
resting potential is maintained by
ungated channels (not shown).
1
Return to resting
state.
Figure 28.4_s1
Membrane potential
(mV)
50
Action
potential
0
50 Threshold
1
100
Resting potential
Time (msec)
1
Resting state: Voltagegated Na and K
channels are closed;
resting potential is
maintained by ungated
channels (not shown).
Na
Na
Sodium Potassium
channel channel
Outside
of neuron
Plasma membrane
K
Inside of neuron
Figure 28.4_s2
Membrane potential
(mV)
50
Action
potential
0
2
50 Threshold
1
100
Resting potential
Time (msec)
2 A stimulus opens some Na
channels; if threshold is reached,
an action potential is triggered.
Na
Na
K
Figure 28.4_s3
Membrane potential
(mV)
50
Action
potential
3
0
2
50 Threshold
1
100
Resting potential
Time (msec)
3
Additional Na channels
open, K channels are
closed; interior of cell
becomes more positive.
Na
Na
K
Figure 28.4_s4
Membrane potential
(mV)
50
Action
potential
3
0
4
2
50 Threshold
1
100
Resting potential
Time (msec)
4
Na channels close
and inactivate; K
channels open, and
K rushes out;
interior of cell is more
negative than outside.
Na
Na
K
Figure 28.4_s5
Membrane potential
(mV)
50
Action
potential
3
0
2
50 Threshold
1
100
Resting potential
Time (msec)
5
The K channels
close relatively
slowly, causing a
brief undershoot.
4
5
Figure 28.4_s6
Membrane potential
(mV)
50
Action
potential
3
0
2
50 Threshold
1
1
100
5
Resting potential
Time (msec)
1 Return to resting
Na
4
Na
state.
K
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
Action
potential
Na
Plasma
membrane
Axon
segment
1
Na
Figure 28.5_s2
Action
potential
Na
Plasma
membrane
Axon
segment
1
Na
Action potential
Na
K
2
K
Na
Figure 28.5_s3
Action
potential
Na
Plasma
membrane
Axon
segment
1
Na
Action potential
Na
K
2
K
Na
Action potential
Na
K
3
K
Na
Figure 28.5
Axon
Plasma
membrane
Action

Na potential
Axon
segment
1
Na
Action potential
Na
K
2
K
Na
Action potential
Na
K
3
K
Na
28.5 The action potential propagates itself along
the axon
 The frequency of action potentials (but not their
strength) changes with the strength of the stimulus.
© 2012 Pearson Education, Inc.
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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28.6 Neurons communicate at synapses
 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.
Animation: Synapse
© 2012 Pearson Education, Inc.
Figure 28.6
1
Sending cell
Axon of
sending
cell
Synaptic
terminal
of sending
cell
Action
potential
arrives
Synaptic
vesicles
Synaptic
terminal
2
3
Vesicle fuses
with plasma
membrane
Dendrite
of receiving
cell
Neurotransmitter
is released into
synaptic cleft
Synaptic
cleft
4
Neurotransmitter
binds to receptor
Receiving
cell
Ion channels
Neurotransmitter
molecules
Neurotransmitter
Receptor
Neurotransmitter broken
down and released
Ions
5
Ion channel opens
6
Ion channel closes
Figure 28.6_1
1
Sending cell
Axon of
sending
cell
Synaptic
terminal
of sending
cell
Action
potential
arrives
Synaptic
vesicles
Synaptic
terminal
2
Vesicle fuses
with plasma
membrane
Dendrite
of receiving
cell
3
Neurotransmitter
is released into
synaptic cleft
Synaptic
cleft
4
Receiving
cell
Neurotransmitter
binds to receptor
Ion channels
Neurotransmitter
molecules
Figure 28.6_2
Neurotransmitter
Receptor
Neurotransmitter broken
down and released
Ions
5
Ion channel opens
6
Ion channel closes