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Chapter 48
Nervous Systems
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In vertebrates, the central nervous system
consists of a brain and dorsal spinal cord
• The PNS connects to the CNS
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Information Processing
• Nervous systems process information in three
stages: sensory input, integration, and motor
output
Sensory input
Sensor
Integration
Motor output
Effector
Peripheral nervous
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
system (PNS)
Central nervous
system (CNS)
LE 48-4
Quadriceps
muscle
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
Neuron Structure
• Most of a neuron’s organelles are in the cell body
• Most neurons have dendrites, highly branched
extensions that receive signals from other neurons
• The axon is typically a much longer extension that
transmits signals to other cells at synapses
• Many axons are covered with a myelin sheath
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-5
Dendrites
Cell body
Nucleus
Axon hillock Axon
Presynaptic cell
Signal
direction
Synaptic
Myelin sheath terminals
Synapse
Postsynaptic cell
LE 48-6
Dendrites
Axon
Cell
body
Sensory neuron
Interneurons
Motor neuron
Supporting Cells (Glia)
• Glia are essential for structural integrity of the
nervous system and for functioning of neurons
• Types of glia: astrocytes, radial glia,
oligodendrocytes, and Schwann cells
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• In the CNS, astrocytes provide structural support
for neurons and regulate extracellular
concentrations of ions and neurotransmitters
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-8
Nodes of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Myelin sheath
Nodes of
Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 µm
Concept 48.2: Ion pumps and ion channels
maintain the resting potential of a neuron
• Across its plasma membrane, every cell has a voltage
called a membrane potential
• The cell’s inside is negative relative to the outside
Microelectrode
–70 mV
Voltage
recorder
Reference
electrode
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The Resting Potential
• Resting potential is the membrane potential of a
neuron that is not transmitting signals
• Resting potential depends on ionic gradients
across the plasma membrane
Animation: Resting Potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-10
CYTOSOL
EXTRACELLULAR
FLUID
[Na+]
15 mM
[Na+]
150 mM
[K+]
150 mM
[K+]
5 mM
[Cl–]
[Cl–]
120 mM
10 mM
[A–]
100 mM
Plasma
membrane
LE 48-11
Inner
chamber
–92 mV
Outer
chamber
150 mM
KCl
Inner
chamber
15 mM
NaCl
5 mM
KCl
+62 mV
Outer
chamber
150 mM
NaCl
Cl–
K+
Potassium
channel
Cl–
Na+
Sodium
channel
Artificial
membrane
Membrane selectively permeable to K+
Membrane selectively permeable to Na+
Gated Ion Channels
• Gated ion channels open or close in response to
one of three stimuli:
– Stretch-gated ion channels open when the
membrane is mechanically deformed
– Ligand-gated ion channels open or close
when a specific chemical binds to the channel
– Voltage-gated ion channels respond to a
change in membrane potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 48.3: Action potentials are the signals
conducted by axons
• If a cell has gated ion channels, its membrane
potential may change in response to stimuli that
open or close those channels
• Some stimuli trigger a hyperpolarization, an
increase in magnitude of the membrane potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Other stimuli trigger a depolarization, a reduction
in the magnitude of the membrane potential
Stimuli
Stimuli
+50
–50 Threshold
Resting
potential
Hyperpolarizations
0 1 2 3 4 5
Time (msec)
Graded potential hyperpolarizations
+50
Membrane potential (mV)
0
Membrane potential (mV)
Membrane potential (mV)
+50
–100
Stronger depolarizing stimulus
0
–50 Threshold
Resting
potential
0 1 2 3 4 5
Time (msec)
Graded potential depolarizations
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0
–50 Threshold
Resting
potential
Depolarizations
–100
Action
potential
–100
0 1 2 3 4 5 6
Time (msec)
Action potential
Production of Action Potentials
• Depolarizations are usually graded only up to a
certain membrane voltage, called the threshold
• A stimulus strong enough to produce
depolarization that reaches the threshold triggers
a response called an action potential
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• An action potential is a brief all-or-none
depolarization of a neuron’s plasma membrane
• It carries information along axons
Dendrites
Cell body
Nucleus
Axon hillock Axon
Presynaptic cell
Signal
direction
Synaptic
Myelin sheath terminals
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Synapse
Postsynaptic cell
LE 48-13_5
Na+
Na+
Na+
Na+
K+
K+
Rising phase of the action potential
Falling phase of the action potential
Na+
Na+
Membrane potential
(mV)
+50
0
–50
K+
Action
potential
–100
Threshold
Resting potential
Time
Depolarization
Na+
Na+
Extracellular fluid
Na+
Potassium
channel
Activation
gates
K+
Plasma membrane
Cytosol
Resting state
Undershoot
Sodium
channel
K+
Inactivation
gate
Animation: Action Potential
Conduction of Action Potentials
• An action potential
can travel long
distances by
regenerating itself
along the axon
Axon
Action
potential
Na+
An action potential is generated as Na+ flows inward
across the membrane at one location.
K+
Action
potential
Na+
K+
The depolarization of the action potential spreads to the
neighboring region of the membrane, re-initiating the
action potential there. To the left of this region, the
membrane is repolarizing as K+ flows outward.
K+
Action
potential
Na+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
K+
The depolarization-repolarization process is repeated in the
next region of the membrane. In this way, local currents of
ions across the plasma membrane cause the action
potential to be propagated along the length of the axon.
LE 48-15
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
Concept 48.4: Neurons communicate with other
cells at synapses
• In an electrical synapse, current flows directly
from one cell to another via a gap junction
• The vast majority of synapses are chemical
synapses
• In a chemical synapse, a presynaptic neuron
releases chemical neurotransmitters stored in
the synaptic terminal
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LE 48-16
Synaptic
terminals
of presynaptic
neurons
5 µm
Postsynaptic
neuron
LE 48-17
Presynaptic
cell
Postsynaptic cell
Synaptic vesicles
containing
neurotransmitter
Na+
K+
Presynaptic
membrane
Neurotransmitter
Postsynaptic
membrane
Ligandgated
ion channel
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
Ca2+
Synaptic cleft
Ligand-gated
ion channels
Animation: Synapse
Direct Synaptic Transmission
• Direct synaptic transmission involves binding of
neurotransmitters to ligand-gated ion channels
• Neurotransmitter binding causes ion channels to
open, generating a postsynaptic potential
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Acetylcholine
• Acetylcholine is a common neurotransmitter in
vertebrates and invertebrates
• It can be inhibitory or excitatory
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Biogenic Amines
• Biogenic amines include epinephrine,
norepinephrine, dopamine, and serotonin
• They are active in the CNS and PNS
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 48.5: The vertebrate nervous system is
regionally specialized
• Vertebrate nervous systems show a high degree
of cephalization and distinct CNS and PNS
nervous
Peripheral nervous
components Central
system (CNS)
system (PNS)
Brain
Spinal cord
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
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LE 48-20
Gray matter
White
matter
Ventricles
The Peripheral Nervous System
• The PNS transmits information to and from the
CNS and regulates movement and internal
environment
• The PNS has two functional components: the
somatic and autonomic nervous systems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-21
Peripheral
nervous system
Somatic
nervous
system
Autonomic
nervous
system
Sympathetic
division
Parasympathetic
division
Enteric
division
• The sympathetic division correlates with the
“fight-or-flight” response
• The parasympathetic division promotes a return
to self-maintenance functions
• The enteric division controls activity of the
digestive tract, pancreas, and gallbladder
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-22
Sympathetic division
Parasympathetic division
Action on target organs:
Location of
preganglionic neurons:
brainstem and sacral
segments of spinal cord
Neurotransmitter
released by
preganglionic neurons:
acetylcholine
Location of
postganglionic neurons:
in ganglia close to or
within target organs
Action on target organs:
Dilates pupil
of eye
Constricts pupil
of eye
Inhibits salivary
gland secretion
Stimulates salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Accelerates heart
Slows heart
Stimulates activity
of stomach and
intestines
Inhibits activity of
stomach and intestines
Thoracic
Inhibits activity
of pancreas
Stimulates activity
of pancreas
Stimulates
gallbladder
Stimulates glucose
release from liver;
inhibits gallbladder
Neurotransmitter
released by
preganglionic neurons:
acetylcholine
Location of
postganglionic neurons:
some in ganglia close to
target organs; others in
a chain of ganglia near
spinal cord
Lumbar
Neurotransmitter
released by
postganglionic neurons:
Promotes emptying
acetylcholine
of bladder
Promotes erection
of genitalia
Relaxes bronchi
in lungs
Location of
preganglionic neurons:
thoracic and lumbar
segments of spinal cord
Stimulates
adrenal medulla
Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation and
vaginal contractions
Neurotransmitter
released by
postganglionic neurons:
norepinephrine
The Brainstem
• The brainstem has three parts: the medulla
oblongata, the pons, and the midbrain
• The medulla oblongata contains centers that
control several visceral functions
• The pons also participates in visceral functions
• The midbrain contains centers for receipt and
integration of sensory information
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 48-24
Eye
Input
from ears
Reticular formation
Input from touch,
pain, and temperature
receptors
The Cerebellum
• The cerebellum is important for coordination and
error checking during motor, perceptual, and
cognitive functions
• It is also involved in learning and remembering
motor skills
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The Diencephalon
• The diencephalon develops into three regions: the
epithalamus, thalamus, and hypothalamus
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The Cerebrum
• The cerebrum develops from the embryonic
telencephalon
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LE 48-26
Left cerebral
hemisphere
Right cerebral
hemisphere
Corpus
callosum
Basal
nuclei
Neocortex
• In humans, the cerebral cortex is the largest and
most complex part of the brain
• Here sensory information is analyzed, motor
commands are issued, and language is generated
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Concept 48.6: The cerebral cortex controls
voluntary movement and cognitive functions
• Each side of the cerebral cortex has four lobes:
frontal, parietal, temporal, and occipital
• Each lobe contains primary sensory areas and
association areas
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LE 48-27
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Taste
Somatosensory
association
area
Reading
Speech
Hearing
Smell
Temporal lobe
Auditory
association
area
Visual
association
area
Vision
Occipital lobe
LE 48-28
Frontal lobe
Parietal lobe
Toes
Genitalia
Lips
Jaw
Tongue
Pharynx
Primary
motor cortex
Abdominal
organs
Primary
somatosensory
cortex
LE 48-29
Max
Hearing
words
Seeing
words
Min
Speaking
words
Generating
words