Download AP Biology Chapter 48 Neurons Guided Notes

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 48
Neurons, Synapses, and Signaling
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Lines of Communication
• The cone snail kills prey with venom that
disables neurons
• __________________are nerve cells that
transfer information within the body
• Neurons use two types of signals to
communicate: _____________(long-distance)
and ___________________ (short-distance)
© 2011 Pearson Education, Inc.
Figure 48.1
• Interpreting signals in the nervous system
involves sorting a complex set of ____________
_____________________
• Processing of information takes place in simple
clusters of neurons called ____________ or a
more complex organization of neurons called a
____________
© 2011 Pearson Education, Inc.
Concept 48.1: Neuron organization and
structure reflect function in information
transfer
• The __________ possesses extremely large
nerve cells and has played a crucial role in the
discovery of how neurons transmit signals
© 2011 Pearson Education, Inc.
Introduction to Information Processing
• Nervous systems process information in three
stages:_______________________________
________________________
© 2011 Pearson Education, Inc.
Figure 48.2
Nerves
with giant axons
Ganglia
Brain
Arm
Eye
Nerve
Mantle
• Sensors detect external stimuli and internal
conditions and transmit information along
______________________
• Sensory information is sent to the brain or
ganglia, where _______________ integrate the
information
• Motor output leaves the brain or ganglia via
___________________ , which trigger muscle
or gland activity
© 2011 Pearson Education, Inc.
• Many animals have a complex nervous system
that consists of
– A ______________________________where
integration takes place; this includes the brain
and a nerve cord
– A _______________________________, which
carries information into and out of the CNS
– The neurons of the PNS, when bundled
together, form ____________
© 2011 Pearson Education, Inc.
Figure 48.3
Sensory input
Integration
Sensor
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Neuron Structure and Function
• Most of a neuron’s organelles are in the ______
_____________
• Most neurons have ______________, highly
branched extensions that receive signals from
other neurons
• The ________ is typically a much longer
extension that transmits signals to other cells at
_____________
• The cone-shaped base of an axon is called the
________________
© 2011 Pearson Education, Inc.
Figure 48.4
Dendrites
Stimulus
Axon hillock
Nucleus
Cell
body
Presynaptic
cell
Axon
Signal
direction
Synapse
Neurotransmitter
Synaptic terminals
Postsynaptic cell
Synaptic
terminals
• The __________________ of one axon passes
information across the synapse in the form of
chemical messengers called _______________
• A ________________ is a junction between an
axon and another cell
© 2011 Pearson Education, Inc.
• Information is transmitted from a ____________
_______________ (a neuron) to a __________
_____________ (a neuron, muscle, or gland cell)
• Most neurons are nourished or insulated by cells
called ____________
© 2011 Pearson Education, Inc.
Figure 48.5
Dendrites
Axon
Cell
body
Portion
of axon
Sensory neuron
Interneurons
Motor neuron
Figure 48.6
80 m
Glia
Cell bodies of neurons
Concept 48.2: Ion pumps and ion channels
establish the resting potential of a neuron
• Every cell has a voltage (difference in electrical
charge) across its plasma membrane called a
________________________
• The ________________ is the membrane
potential of a neuron not sending signals
• Changes in __________________ act as
signals, transmitting and processing information
© 2011 Pearson Education, Inc.
Formation of the Resting Potential
• In a mammalian neuron at resting potential, the
concentration of ___ is highest inside the cell,
while the concentration of ____ is highest
outside the cell
• _______________________ use the energy of
ATP to maintain these K+ and Na+ gradients
across the plasma membrane
• These concentration gradients represent
______________________
© 2011 Pearson Education, Inc.
• The opening of _______________in the plasma
membrane converts ______________ potential to
______________ potential
• A neuron at resting potential contains many open
____ channels and fewer open ___channels; ___
diffuses out of the cell
• The resulting buildup of ____________________
within the neuron is the major source of
membrane potential
© 2011 Pearson Education, Inc.
Table 48.1
Figure 48.7
Key
Na
K
Sodiumpotassium
pump
OUTSIDE
OF CELL
Potassium
channel
Sodium
channel
INSIDE
OF CELL
Modeling the Resting Potential
• Resting potential can be modeled by an artificial
membrane that separates two chambers
– The concentration of KCl is higher in the ______
chamber and lower in the outer chamber
– ____ diffuses down its gradient to the outer
chamber
– Negative charge (___) builds up in the inner
chamber
• At equilibrium, both the electrical and chemical
gradients are balanced
© 2011 Pearson Education, Inc.
Figure 48.8a
Inner
chamber
90 mV
140 mM
KCl
Outer
chamber
5 mM
KCl
K
Potassium
channel
Cl
Artificial
membrane
(a) Membrane selectively permeable
to K
EK  62 mV
 90 mV
• The _____________________is the membrane
voltage for a particular ion at equilibrium and can
be calculated using the __________ equation
Eion = 62 mV (log[ion]outside/[ion]inside)
• The equilibrium potential of K+ (EK) is ________,
while the equilibrium potential of Na+ (ENa) is
_____________
© 2011 Pearson Education, Inc.
• In a resting neuron, the currents of K+ and Na+
are ________________, and the resting
potential across the membrane remains steady
© 2011 Pearson Education, Inc.
Figure 48.8b
Inner
chamber
15 mM
NaCl
62 mV
Outer
chamber
150 mM
NaCl
Cl
Na
Sodium
channel
(b) Membrane selectively permeable
to Na
ENa  62 mV
 62 mV
Concept 48.3: Action potentials are the
signals conducted by axons
• Changes in membrane potential occur because
neurons contain __________________ that open
or close in response to stimuli
© 2011 Pearson Education, Inc.
Hyperpolarization and Depolarization
• When gated ________________ open, K+
diffuses________, making the inside of the cell
more negative
• This is__________________, an increase in
magnitude of the membrane potential
© 2011 Pearson Education, Inc.
Figure 48.10a
(a) Graded hyperpolarizations
produced by two stimuli
that increase membrane
permeability to K
Stimulus
Membrane potential (mV)
50
0
50 Threshold
100
Resting
potential
Hyperpolarizations
0 1 2 3 4 5
Time (msec)
• Opening other types of ion channels triggers a
_________________, a reduction in the
magnitude of the membrane potential
• For example, depolarization occurs if ________
___________________ and Na+ diffuses into the
cell
© 2011 Pearson Education, Inc.
Figure 48.10b
(b) Graded depolarizations
produced by two stimuli
that increase membrane
permeability to Na
Stimulus
Membrane potential (mV)
50
0
50 Threshold
100
Resting
potential
Depolarizations
0 1 2 3 4 5
Time (msec)
Graded Potentials and Action Potentials
• ___________________ are changes in
polarization where the magnitude of the change
varies with the strength of the stimulus
• These are not the nerve signals that travel along
axons, but they do have an effect on the
generation of nerve signals
© 2011 Pearson Education, Inc.
• If a depolarization shifts the membrane potential
sufficiently, it results in a massive change in
membrane voltage called an ________________
• Action potentials have a constant magnitude, are
____________, and transmit signals over long
distances
• They arise because some ion channels are
____________________, opening or closing
when the membrane potential passes a certain
level
© 2011 Pearson Education, Inc.
Figure 48.10c
(c) Action potential
triggered by a
depolarization that
reaches the threshold
Strong depolarizing stimulus
Membrane potential (mV)
50
Action
potential
0
50 Threshold
Resting
potential
100
0 1 2 3 4 5 6
Time (msec)
Generation of Action Potentials: A Closer
Look
• An action potential can be considered as a
series of stages
• At ___________________
1. Most voltage-gated sodium (Na+) channels are
_____________; most of the voltage-gated
potassium (K+) channels are also __________
© 2011 Pearson Education, Inc.
Figure 48.11-1
Key
Na
K
Membrane potential
(mV)
50
0
Threshold
50
100
OUTSIDE OF CELL
INSIDE OF CELL
Inactivation loop
1 Resting state
Sodium
channel
Potassium
channel
1
Resting potential
Time
• When an _________________ is generated
2. Voltage-gated Na+ channels ________ and Na+
flows __________________
3. During the ________, the threshold is crossed,
and the membrane potential _____________
4. During the ____________, voltage-gated Na+
channels become _____________; voltagegated K+ channels _________, and K+ flows
_________________
© 2011 Pearson Education, Inc.
5. During the _____________, membrane
permeability to _____is at first higher than at
rest, then voltage-gated K+ channels close
and ___________________ is restored
© 2011 Pearson Education, Inc.
Figure 48.11-5
Key
Na
K
Membrane potential
(mV)
Action
potential
OUTSIDE OF CELL
100
Sodium
channel
3
0
50
2 Depolarization
4 Falling phase of the action potential
50
3 Rising phase of the action potential
Threshold
2
1
4
5
Resting potential
Time
Potassium
channel
INSIDE OF CELL
Inactivation loop
1 Resting state
5 Undershoot
1
Figure 48.11a
Membrane potential
(mV)
50
Action
potential
3
0
50
100
2
4
Threshold
1
Resting potential
Time
5
1
• During the ________________ after an action
potential, a second action potential cannot be
initiated
• The refractory period is a result of a temporary
inactivation of the __________________
© 2011 Pearson Education, Inc.
Conduction of Action Potentials
• At the site where the action potential is
generated, usually the axon hillock, an electrical
current _________________ the neighboring
region of the axon membrane
• Action potentials travel in only one direction:
toward the ____________________
© 2011 Pearson Education, Inc.
• _______________________ behind the zone of
depolarization prevent the action potential from
traveling backwards
© 2011 Pearson Education, Inc.
Figure 48.12-3
Axon
Plasma
membrane
Action
potential
1
Na
K
2
Cytosol
Action
potential
Na
K
K
3
Action
potential
Na
K
Evolutionary Adaptation of Axon Structure
• The speed of an action potential increases with
the ___________________
• In vertebrates, axons are insulated by a ______
________________, which causes an action
potential’s speed to increase
• Myelin sheaths are made by glia—
____________________in the CNS and
_____________________in the PNS
© 2011 Pearson Education, Inc.
Figure 48.13
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Myelin sheath
Nodes of
Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 m
• Action potentials are formed only at ________
_______________, gaps in the myelin sheath
where voltage-gated Na+ channels are found
• Action potentials in myelinated axons jump
between the nodes of Ranvier in a process
called _______________________
© 2011 Pearson Education, Inc.
Figure 48.14
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
Concept 48.4: Neurons communicate with
other cells at synapses
• At __________________, the electrical current
flows from one neuron to another
• At __________________, a chemical
neurotransmitter carries information across the
gap junction
• Most synapses are ______________synapses
© 2011 Pearson Education, Inc.
• The presynaptic neuron synthesizes and
packages the neurotransmitter in _________
_____________located in the synaptic terminal
• The action potential causes the release of the
___________________
• The neurotransmitter diffuses across the
____________________and is received by the
postsynaptic cell
© 2011 Pearson Education, Inc.
Figure 48.15
Presynaptic
cell
Postsynaptic cell
Axon
Synaptic vesicle
containing
neurotransmitter
1
Postsynaptic
membrane
Synaptic
cleft
Presynaptic
membrane
3
K
Ca2 2
Voltage-gated
Ca2 channel
Ligand-gated
ion channels
4
Na
Generation of Postsynaptic Potentials
• Direct synaptic transmission involves binding of
neurotransmitters to _____________________
in the postsynaptic cell
• Neurotransmitter binding causes ion channels to
open, generating a _______________________
© 2011 Pearson Education, Inc.
• Postsynaptic potentials fall into two categories
– ____________________________________
are depolarizations that bring the membrane
potential toward threshold
– ____________________________________
are hyperpolarizations that move the membrane
potential farther from threshold
© 2011 Pearson Education, Inc.
• After release, the neurotransmitter
– May diffuse out of the __________________
– May be ___________ by surrounding cells
– May be degraded by _________________
© 2011 Pearson Education, Inc.
Summation of Postsynaptic Potentials
• Most neurons have ______________on their
dendrites and cell body
• A single EPSP is usually ________________ to
trigger an action potential in a postsynaptic
neuron
© 2011 Pearson Education, Inc.
• If two EPSPs are produced in rapid succession,
an effect called ____________________occurs
© 2011 Pearson Education, Inc.
Figure 48.17a
Terminal branch
of presynaptic
neuron
E1
E2
E2
Postsynaptic
neuron
Membrane potential (mV)
E1
Axon
hillock
I
I
0
Action
potential
Threshold of axon of
postsynaptic neuron
Resting
potential
70
E1
E1
(a) Subthreshold, no
summation
E1 E1
(b) Temporal summation
• In________________, EPSPs produced nearly
simultaneously by different synapses on the
same postsynaptic neuron add together
• The combination of EPSPs through ________
and _______________ summation can trigger
an action potential
© 2011 Pearson Education, Inc.
Figure 48.17b
E1
E1
E2
E2
I
I
Action
potential
E1  E2
(c) Spatial summation
E1
I
E1  I
(d) Spatial summation
of EPSP and IPSP
• Through summation, an IPSP can ___________
the effect of an EPSP
• The ________________ of EPSPs and IPSPs
determines whether an axon hillock will reach
threshold and generate an action potential
© 2011 Pearson Education, Inc.
Modulated Signaling at Synapses
• In some synapses, a neurotransmitter binds to a
receptor that is ___________________
• In this case, movement of ions through a
channel depends on one or more ___________
_________________
© 2011 Pearson Education, Inc.
• Binding of a neurotransmitter to a metabotropic
receptor activates a signal transduction pathway
in the postsynaptic cell involving a ___________
_________________
• Compared to ligand-gated channels, the
effects of second-messenger systems have a
_________________ but _______________
© 2011 Pearson Education, Inc.
Neurotransmitters
• There are more than ______________________,
belonging to five groups: acetylcholine, biogenic
amines, amino acids, neuropeptides, and
gases
• A single neurotransmitter may have more than a
____________ different receptors
© 2011 Pearson Education, Inc.
Table 48.2
Acetylcholine
• ____________________ is a common
neurotransmitter in vertebrates and invertebrates
• It is involved in muscle stimulation, memory
formation, and learning
• Vertebrates have two major classes of
acetylcholine receptor, one that is ___________
and one that is _________________
© 2011 Pearson Education, Inc.
Amino Acids
• ____________________________are active in
the CNS and PNS
• Known to function in the CNS are
– ______________________________
– ______________________________
– _______________
© 2011 Pearson Education, Inc.
Biogenic Amines
• _____________________include
– ________________
– ________________
– ________________
– ________________
• They are active in the CNS and PNS
© 2011 Pearson Education, Inc.
Neuropeptides
• Several ________________, relatively short
chains of amino acids, also function as
neurotransmitters
• Neuropeptides include substance P and
_________________, which both affect our
perception of pain
• ________________ bind to the same receptors
as endorphins and can be used as painkillers
© 2011 Pearson Education, Inc.
Figure 48.18
EXPERIMENT
Radioactive
naloxone
1 Radioactive naloxone and
a test drug are incubated
with a protein mixture.
Drug
Protein
mixture
2 Proteins are trapped on a filter.
Bound naloxone is detected
by measuring radioactivity.
RESULTS
Drug
Opiate
Concentration That Blocked
Naloxone Binding
Morphine
Yes
6  109 M
Methadone
Yes
2  108 M
Levorphanol
Yes
2  109 M
Phenobarbital
No
No effect at 104 M
Atropine
No
No effect at 104 M
Serotonin
No
No effect at 104 M
Figure 48.18a
EXPERIMENT
Radioactive
naloxone
1 Radioactive naloxone and
a test drug are incubated
with a protein mixture.
Drug
Protein
mixture
2 Proteins are trapped on a filter.
Bound naloxone is detected
by measuring radioactivity.
Figure 48.18b
RESULTS
Drug
Opiate
Concentration That Blocked
Naloxone Binding
Morphine
Yes
6  109 M
Methadone
Yes
2  108 M
Levorphanol
Yes
2  109 M
Phenobarbital
No
No effect at 104 M
Atropine
No
No effect at 104 M
Serotonin
No
No effect at 104 M
Gases
• Gases such as ________________and ______
_____________are local regulators in the PNS
© 2011 Pearson Education, Inc.