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Chapter 48 and 49
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1. What are neurons?
Neurons are nerve cells that transfer information within the body
Neurons use two types of signals to communicate: electrical signals (long-distance)
and chemical signals (short-distance)
2. What are the three stages in which the nervous systems process information?
Briefly describe them.
Nervous systems process information in three stages: sensory input, integration, and
motor output
•
Sensors detect external stimuli and internal conditions and transmit information
along sensory neurons
•
Sensory information is sent to the brain or ganglia, where interneurons integrate
the information
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Motor output leaves the brain or ganglia via motor neurons, which trigger muscle or
gland activity
3. Many animals have a complex nervous system that consists of a CNS and a PNS.
What are they?
a. A central nervous system (CNS) where integration takes place; this
includes the brain and a nerve cord
b. A peripheral nervous system (PNS), which brings information into and out
of the CNS
4. Draw and label a typical nerve cell below. Make sure to label and briefly describe
the following parts: cell body, dendrites, axon, axon hillock, synapse, synaptic
terminal, presynaptic and postsynaptic cell, and glia.
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Most of a neuron’s organelles are in the cell body
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Most neurons have dendrites, highly branched extensions that receive signals from
other neurons
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The axon is typically a much longer extension that transmits signals to other cells
at synapses
•
An axon joins the cell body at the axon hillock
•
A synapse is a junction between an axon and another cell
•
The synaptic terminal of one axon passes information across the synapse in the
form of chemical messengers called neurotransmitters
Chapter 48 and 49
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Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic
cell (a neuron, muscle, or gland cell)
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Most neurons are nourished or insulated by cells called glia
Fig. 48-4
Dendrites
Stimulus
Nucleus
Cell
body
Axon
hillock
Presynaptic
cell
Axon
Synapse
Synaptic terminals
Postsynaptic cell
Neurotransmitter
5. What is a membrane potential? What is the resting potential?
Every cell has a voltage (difference in electrical charge) across its plasma membrane
called a membrane potential. Messages are transmitted as changes in membrane
potential. The resting potential is the membrane potential of a neuron not sending
signals
Chapter 48 and 49
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6. What is the principal cation inside the cell? outside the cell? What does this do to
the charge inside and outside of the cell?
In a mammalian neuron at resting potential, the concentration of K+ is greater inside the
cell, while the concentration of Na+ is greater outside the cell
Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients
across the plasma membrane
These concentration gradients represent chemical potential energy
7.
Which side of the membrane has a negative charge?
Anions trapped inside the cell contribute to the negative charge within the neuron
Key
+
Na
K
+
Sodiumpotassiu
m
pump
OUTSIDE
CELL
+
OUTSIDE
[K ]
CELL
5 mM
INSIDE
CELL
+
[K ]
140 mM
+
–
[Na ]
[Cl ]
150 mM 120 mM
+
[Na ]
15 mM
–
[Cl ]
10 mM
–
[A ]
100 mM
INSIDE
CELL
(a)
(b)
8. What pump is used to maintain the gradients across the membrane?
Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients
across the plasma membrane
Po
ch
Chapter 48 and 49
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9. What change in the permeability of the cell’s membrane to K+ and/or Na+ could
cause the cell’s membrane potential to shift from -70mV to -90mV?
The opening of ion channels in the plasma membrane converts chemical potential to
electrical potential
A neuron at resting potential contains many open K+ channels and fewer open Na+ channels;
K+ diffuses out of the cell
10. What is hyperpolarization? How does it occur?
Membrane potential changes in response to opening or closing of these channels
When gated K+ channels open, K+ diffuses out, making the inside of the cell more negative
This is hyperpolarization, an increase in magnitude of the membrane potential
11. What is depolarization? How does it occur?
Other stimuli trigger a depolarization, a reduction in the magnitude of the membrane
potential
For example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the
cell
12. What is a graded potential?
Graded potentials are changes in polarization where the magnitude of the change varies
with the strength of the stimulus
13. What is an action potential? What role does a threshold plays in an action
potential?
Voltage-gated Na+ and K+ channels respond to a change in membrane potential
When a stimulus depolarizes the membrane, Na+ channels open, allowing Na+ to diffuse into
the cell
The movement of Na+ into the cell increases the depolarization and causes even more Na+
channels to open
A strong stimulus results in a massive change in membrane voltage called an action
potential
An action potential occurs if a stimulus causes the membrane voltage to cross a particular
threshold
An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane
Action potentials are signals that carry information along axons
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14. The following diagram shows the changes in voltage-gated channels during an action
potential. Label the channels and inactivation gate, ions, and the components of the
graph. Name and describe the five phases of the action potential Place numbers on
the graph to show where each phase is occurring. After labeling the diagram, you
should be able to tell me about the rising and falling phase, the undershoot, and
the refractory period.
Fig. 48-10-5
Key
Na
+
+
K
3
4
Rising phase of the action potential
Fa
+50
Action
potential
Membrane potential
(mV)
3
0
2
–50
4
Threshold
1
1
5
2
Depolarization
Extracellular fluid
–100
Sodium
channel
Resting
potential
Time
Potassium
channel
Plasma
membrane
Cytosol
Inactivation loop
5
1
Resting
state
Undersho
Chapter 48 and 49
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At resting potential
1. Most voltage-gated Na+ and K+ channels are closed, but some K+ channels (not
voltage-gated) are open
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When an action potential is generated
2. Voltage-gated Na+ channels open first and Na+ flows into the cell
3. During the rising phase, the threshold is crossed, and the membrane
potential increases
4. During the falling phase, voltage-gated Na+ channels become inactivated;
voltage-gated K+ channels open, and K+ flows out of the cell
5. During the undershoot, membrane permeability to K+ is at first higher
than at rest, then voltage-gated K+ channels close; resting potential is restored
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During the refractory period after an action potential, a second action potential
cannot be initiated
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The refractory period is a result of a temporary inactivation of the Na+ channels
15. Where is an action potential generally generated? Why does the action potential
only travel in one direction?
An action potential can travel long distances by regenerating itself along the axon
At the site where the action potential is generated, usually the axon hillock, an electrical
current depolarizes the neighboring region of the axon membrane
•
Inactivated Na+ channels behind the zone of depolarization prevent the action
potential from traveling backwards
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Action potentials travel in only one direction: toward the synaptic terminals
16. What factors affect the conduction speed of a action potential?
The speed of an action potential increases with the axon’s diameter
In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s
speed to increase, Myelin sheaths are made by glia— oligodendrocytes in the CNS and
Schwann cells in the PNS
17. What are the two types of synapse? What is the difference between the two?
At electrical synapses, the electrical current flows from one neuron to another
At chemical synapses, a chemical neurotransmitter carries information across the gap
junction
Most synapses are chemical synapses
Chapter 48 and 49
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18. How does the signal get transferred from the presynaptic to the postsynaptic
neurons across a chemical synapse? In other words, what does the presynaptic
neuron synthesize and how does this cause a response in the postsynaptic neuron?
The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic
vesicles located in the synaptic terminal
The action potential causes the release of the neurotransmitter
The neurotransmitter diffuses across the synaptic cleft and is received by the
postsynaptic cell.
Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion
channels in the postsynaptic cell
Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential
19. What are the two types of postsynaptic potentials? Describe them briefly.
a. Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring
the membrane potential toward threshold
b. Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move
the membrane potential farther from threshold
20. What is a temporal summation? What is spatial summation? What is the difference
between the two and what will the combination of them trigger?
A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron
If two EPSPs are produced in rapid succession, an effect called temporal summation
occurs.
In spatial summation, EPSPs produced nearly simultaneously by different synapses on the
same postsynaptic neuron add together
The combination of EPSPs through spatial and temporal summation can trigger an action
potential
Through summation, an IPSP can counter the effect of an EPSP
The summed effect of EPSPs and IPSPs determines whether an axon hillock will reach
threshold and generate an action potential
21. What is modulated synaptic transmission? What kind of effects can this indirect
synaptic transmission have?
In indirect synaptic transmission, a neurotransmitter binds to a receptor that is not
part of an ion channel
Chapter 48 and 49
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This binding activates a signal transduction pathway involving a second messenger in the
postsynaptic cell
Effects of indirect synaptic transmission have a slower onset but last longer
22. Complete the chart below.
Neurotransmitter
Acetylcholine
Function
•
Example
Acetylcholine is a
common
neurotransmitter in
vertebrates and
invertebrates
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In vertebrates it is
usually an excitatory
transmitter
Biogenic amines
•
Biogenic amines
epinephrine, norepinephrine,
include epinephrine,
dopamine, and serotonin
norepinephrine,
dopamine, and
serotonin
•
They are active in
the CNS and PNS
Amino acids
•
Two amino acids are
known to function as
major
neurotransmitters in
the CNS: gammaaminobutyric acid
(GABA) and
glutamate
Neuropeptides
•
Several
•
Neuropeptides
neuropeptides,
include substance P
relatively short
and endorphins,
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chains of amino acids,
which both affect
also function as
our perception of
neurotransmitters
pain
Opiates bind to the
same receptors as
endorphins and can
be used as painkillers
Gases
•
Gases such as nitric
oxide and carbon
monoxide are local
regulators in the PNS
Chapter 49
23. What is a nerve net?
A nerve net is a series of interconnected nerve cells
More complex animals have nerves
24. Bilaterally symmetrical animals exhibit
. Define this term below.
Bilaterally symmetrical animals exhibit cephalization
Cephalization is the clustering of sensory organs at the front end of the body
25. What are ganglia?
Annelids and arthropods have segmentally arranged clusters of neurons called ganglia
26. Sessile molluscs (e.g., clams and chitons) have
systems, whereas
more complex molluscs (e.g., octopuses and squids) have more
systems
Sessile molluscs (e.g., clams and chitons) have simple systems, whereas more complex
molluscs (e.g., octopuses and squids) have more sophisticated systems
27. What is the job of the spinal cord?
The spinal cord conveys information from the brain to the PNS
The spinal cord also produces reflexes independently of the brain
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28. The
of the spinal cord and the
of the brain are
hollow and filled with cerebrospinal fluid.
The central canal of the spinal cord and the ventricles of the brain are hollow and
filled with cerebrospinal fluid
29. What is the difference between gray matter and white matter?
a. Gray matter, which consists of neuron cell bodies, dendrites, and
unmyelinated axons
b. White matter, which consists of bundles of myelinated axons
30. List and briefly describe the types of Glia in the CNS?
a. Ependymal cells promote circulation of cerebrospinal fluid
b. Microglia protect the nervous system from microorganisms
c. Oligodendrocytes and Schwann cells form the myelin sheaths around axons
d. Astrocytes provide structural support for neurons, regulate extracellular
ions and neurotransmitters, and induce the formation of a blood-brain
barrier that regulates the chemical environment of the CNS
e. Radial glia play a role in the embryonic development of the nervous system
31. What is the job of the PNS? Describe the difference between afferent neurons
and efferent neurons. Describe it’s two functional components.
The PNS transmits information to and from the CNS and regulates movement and the
internal environment
In the PNS, afferent neurons transmit information to the CNS and efferent neurons
transmit information away from the CNS
32. What is the difference between cranial and spinal nerves?
Cranial nerves originate in the brain and mostly terminate in organs of the head and upper
body
Spinal nerves originate in the spinal cord and extend to parts of the body below the head
•
The PNS has two functional components: the motor system and the autonomic
nervous system
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The motor system carries signals to skeletal muscles and is voluntary
•
The autonomic nervous system regulates the internal environment in an involuntary
manner
Chapter 48 and 49
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33. What are the three divisions of the autonomic nervous system?
The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions
The sympathetic and parasympathetic divisions have antagonistic effects on target organs
The sympathetic division correlates with the “fight-or-flight” response
The parasympathetic division promotes a return to “rest and digest”
The enteric division controls activity of the digestive tract, pancreas, and gallbladder
34. Complete the chart below.
The brainstem coordinates and conducts information between brain centers
Embryonic Region
Brain Region
Commonly called
Description and Importance
Forebrain
Telencephalon
Cerebrum
Outer portion called: cerebral cortex .
Brainstem and cerebrum control
arousal and sleep. Cerebrum develops
from the embryonic telencephalon.
The cerebrum has right and left
cerebral hemispheres
Each cerebral hemisphere consists of a
cerebral cortex (gray matter)
overlying white matter and basal nuclei
In humans, the cerebral cortex is the
largest and most complex part of the
brain
The basal nuclei are important centers
for planning and learning movement
sequences
Diencephalon
Diencephalon
The diencephalon develops into three
regions: the epithalamus, thalamus, and
hypothalamus
The epithalamus includes the pineal
Chapter 48 and 49
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gland and generates cerebrospinal fluid
from blood
The thalamus is the main input center
for sensory information to the
cerebrum and the main output center
for motor information leaving the
cerebrum
The hypothalamus regulates
homeostasis and basic survival
behaviors such as feeding, fighting,
fleeing, and reproducing.
Hypothalamus also regulates circadian
rhythms such as the sleep/wake cycle.
Mammals usually have a pair of
suprachiasmatic nuclei (SCN) in the
hypothalamus that function as a
biological clock
Midbrain
Mesencephalon
Midbrain
Part of brainstem. Brainstem and
cerebrum control arousal and sleep.
core of the brainstem has a diffuse
network of neurons called the reticular
formation
Midbrain contains centers for receipt
and integration of sensory information
Hindbrain
Metencephalon
Pons
Cerebellum
Part of brainstem. Brainstem and
cerebrum control arousal and sleep.
core of the brainstem has a diffuse
network of neurons called the reticular
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formation
Pons regulates breathing centers in
the medulla
Cerebellum is important for
coordination and error checking during
motor, perceptual, and cognitive
functions. It is also involved in learning
and remembering motor skills
Myelencphalon
Medulla
Part of brainstem. Brainstem and
Oblongata
cerebrum control arousal and sleep.
core of the brainstem has a diffuse
network of neurons called the reticular
formation
Medulla oblongata contains centers
that control several functions including
breathing, cardiovascular activity,
swallowing, vomiting, and digestion
35. Label the brain below.
Chapter 48 and 49
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49-9c
Cerebrum (includes cerebral cortex, white matter,
basal nuclei)
Diencephalon (thalamus, hypothalamus, epithalamus)
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Medulla oblongata (part of brainstem)
Diencephalon:
Cerebrum
Hypothalamus
Thalamus
Pineal gland
(part of epithalamus)
Brainstem:
Midbrain
Pons
Pituitary
gland
Medulla
oblongata
Spinal cord
Cerebellum
Central canal
(c) Adult