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1. Which of the following best describes the electrical state of a neuron at rest?
a. The inside of a neuron is more negatively charged than the outside.
b. The outside of a neuron is more negatively charged than the inside.
c. The inside and the outside of a neuron have the same electrical charge.
d. Potassium ions leak into a neuron at rest.
The correct answer is a—The inside of a neuron is more negatively charged than the
outside.
A. Answer a is correct. Due to active transport of Na+ and K+, leakage of K+ and the
presence of intracellular proteins, the inside of the cell is more negative than the
outside.
The correct answer is a—
B. Answer b is incorrect. Due to active transport of Na+ and K+, leakage of K+ and
the presence of intracellular proteins, the inside of the cell is more negative than
the outside.
The correct answer is a—
C. Answer c is incorrect. Due to active transport of Na+ and K+, leakage of K+ and
the presence of intracellular proteins, the inside of the cell is more negative than
the outside.
The correct answer is a—
D. Answer d is incorrect. The concentration of K+ in a neuron at rest is greater inside
than outside, so, if anything, we would predict that K+ would leak out instead.
2. The _____________ cannot be controlled by conscious thought.
a. motor neurons
b. somatic nervous system
c. autonomic nervous system
d. skeletal muscles
The correct answer is c—
A. Answer a is incorrect. The motor neurons are a part of the nervous system under
conscious control.
The correct answer is c—
B. Answer b is incorrect. The somatic nervous system is a part of the nervous system
under conscious control.
The correct answer is c—autonomic nervous system
C. Answer c is correct. The autonomic nervous system functions at a level below
consciousness.
The correct answer is c—
D. Answer d is incorrect. The skeletal muscles are a part of the nervous system under
conscious control.
3. A fight-or-flight response in the body is controlled by the—
a. sympathetic division of the nervous system
b. parasympathetic division of the nervous system
c. release of acetylcholine from postganglionic neurons
d. somatic nervous system
The correct answer is a—sympathetic division of the nervous system
A. Answer a is correct. This is the major mechanism associated with the sympathetic
division of the nervous system.
The correct answer is a—
B. Answer b is incorrect. This is not a mechanism associated with the
parasympathetic digestion, which is instead involved in activities like digestion.
The correct answer is a—
C. Answer c is incorrect. Only some postganglionic neurons release acetylcholine;
some release norepinephrine.
The correct answer is a—
D. Answer d is incorrect. The somatic nervous system involves the motor neurons
that stimulate skeletal muscle contraction.
4. Imagine that you are doing an experiment on the movement of ions across neural
membranes. Which of the following plays a role in determining the equilibrium
concentration of ions across these membranes?
a. Ion concentration gradients.
b. Ion pH gradients.
c. Ion electrical gradients.
d. Both a and c.
The correct answer is d—
A. Answer a is incorrect. Ion concentration gradients are not the sole contributors to
membrane resting potential.
The correct answer is d—
B. Answer b is incorrect. Ion pH gradients are contributors to membrane resting
potential.
The correct answer is d—
C. Answer c is incorrect. It includes only one of the forces—electrical gradients—
that works as a source for establishing the resting membrane potential.
The correct answer is d—Both a and c.
D. Answer d is correct. It includes both ion concentration and electrical gradients as
sources for the resting membrane potential.
5. The Na+/K+ ATPase pump—
a. is not required for action potential firing
b. is important for long-term maintenance of resting potential
c. is important only at the synapse
d. is used to stimulate graded potentials
The correct answer is b—
A. Answer a is incorrect. It is untrue. The Na+/K+ ATPase pump is required to
maintain resting membrane potential, which in turn allows the action potential to
proceed.
The correct answer is b—is important for long-term maintenance of resting potential
B. Answer b is correct. The Na+/K+ ATPase pump is required to maintain the
differences in ion concentration that leads to resting potential via leakage of K+.
The correct answer is b—
C. Answer c is incorrect. The Na+/K+ ATPase pump is found at various sites on the
membrane.
The correct answer is b—
D. Answer d is incorrect. The Na+/K+ ATPase pump does not actually cause graded
potentials.
6. Botox, a derivative of the botulinum toxin that causes food poisoning, inhibits the
release of acetylcholine at the neuromuscular junction. How could this strangesounding treatment produce desired cosmetic effects?
a. By inhibiting the parasympathetic branch of autonomic nervous system
b. By inhibiting the parasympathetic branch of autonomic nervous system
c. By causing paralysis of facial muscles, which decreases wrinkles in the
face
d. By causing facial muscles to contract, whereby the skin is stretched tighter
reducing wrinkles
The correct answer is c—
A. Answer a is incorrect. Neuromuscular junctions are not part of the autonomic
nervous system. Rather they are part of the somatic system that acts through
skeletal muscles.
The correct answer is c—
B. Answer b is incorrect. Neuromuscular junctions are not part of the autonomic
nervous system. Rather they are part of the somatic system that acts through
skeletal muscles.
The correct answer is c—By causing paralysis of facial muscles, which decreases
wrinkles in the face
C. Answer c is correct. Botox is used to temporarily paralyze facial muscles and
reduce facial wrinkling.
The correct answer is c—
D. Answer d is incorrect. The action of Botox should cause paralysis by preventing
contraction, not stimulating it.
7. The following is a list of the components of a chemical synapse. A mutation in
the structure of which of these would affect only the reception of the message, not
its release or the response?
a. Membrane proteins in the postsynaptic cell
b. Proteins in the presynaptic cell
c. Cytoplasmic proteins in the postsynaptic cell
d. Both a and b
The correct answer is a—Membrane proteins in the postsynaptic cell
A. Answer a is correct. A mutation in the membrane receptor protein for
neurotransmitters would prevent the neurotransmitter from binding to the
postsynaptic cell and generating a response.
The correct answer is a—
B. Answer b is incorrect. A mutation in any proteins in the presynaptic cell might
affect the release of the neurotransmitter but not its reception.
The correct answer is a—
C. Answer c is incorrect. A mutation in the cytoplasm of the postsynaptic cell might
affect the response to the neurotransmitter but not its reception.
The correct answer is a—
D. Answer d is incorrect. Answer b is not a correct response.
8. Inhibitory neurotransmitters—
a. hyperpolarize postsynaptic membranes
b. hyperpolarize presynaptic membranes
c. depolarize postsynaptic membranes
d. depolarize presynaptic membranes
The correct answer is a—hyperpolarize postsynaptic membranes
A. Answer a is correct. Inhibitory neurotransmitters prevent postsynaptic cells from
depolarizing. They do this by hyperpolarizing the cell membrane such that the
cell interior becomes more negative than the resting membrane value.
The correct answer is a—
B. Answer b is incorrect. Hyperpolarizing the presynaptic membrane will not prevent
an action potential in the postsynaptic cell, which is the function of inhibitory
neurotransmitters.
The correct answer is a—
C. Answer c is incorrect. Depolarizing the postsynaptic cell will make an action
potential more likely to occur. This would be a stimulatory effect instead of an
inhibitory one.
The correct answer is a—
D. Answer d is incorrect. Depolarizing the presynaptic membrane will not prevent an
action potential in the postsynaptic cell, which is the function of inhibitory
neurotransmitters.
9. Suppose that you stick your finger with a sharp pin. The area affected is very
small and only one pain receptor fires. However, it fires repeatedly at a rapid rate
(it hurts!). This is an example of—
a. temporal summation
b. spatial summation
c. habituation
d. repolarization
The correct answer is a—temporal summation
A. Answer a is correct. Temporal summation is the term used to describe a change in
the timing of firing of the presynaptic cell.
The correct answer is a—
B. Answer b is incorrect. Spatial summation describes the effect of multiple
presynaptic cells firing almost simultaneously.
The correct answer is a—
C. Answer c is incorrect. Habituation occurs when the nervous system becomes
accustomed to a signal and learns to ignore it (no response would be generated).
The correct answer is a—
D. Answer d is incorrect. Repolarization is the process by which a cell is returned to
its resting potential through the action of the Na+/K+ ATPase pump.
10. You are dissecting a rat that died peacefully in its sleep at an advanced age.
Which structure would you NOT expect to find in its brain?
a. Forebrain
b. Midbrain
c. Hindbrain
d. Ventral nerve cords
The correct answer is d—
A. Answer a is incorrect. The forebrain is a part of the vertebrate brain.
The correct answer is d—
B. Answer b is incorrect. The midbrain is a part of the vertebrate brain.
The correct answer is d—
C. Answer c is incorrect. The hindbrain is a part of the vertebrate brain.
The correct answer is d—Ventral nerve cords
D. Answer d is correct. Ventral nerve cords are found in arthropods (insects) not
vertebrate brains.
11. White matter is _________, and gray matter is__________ .
a. comprised of axons; comprised of cell bodies and dendrites
b. myelinated; unmyelinated
c. found in the CNS; also found in the CNS
d. all of the above are correct
The correct answer is d—
A. Answer a is not correct. Although a correct answer, it is only one of three correct
answers to this question.
The correct answer is d—
B. Answer b is not correct. Although a correct answer, it is only one of three correct
answers to this question.
The correct answer is d—
C. Answer c is not correct. Although a correct answer, it is only one of three correct
answers to this question.
The correct answer is d—all of the above are correct
D. Answer d is correct. White matter is composed of myelinated axons, which are
found within the central nervous system. Gray matter is also within the CNS and
is composed of unmyelinated cell bodies.
12. A functional reflex requires—
a. only a sensory neuron and a motor neuron
b. a sensory neuron, the thalamus, and a motor neuron
c. the cerebral cortex and a motor neuron
d. only the cerebral cortex and the thalamus
The correct answer is a—only a sensory neuron and a motor neuron
A. Answer a is correct. A functional reflex requires only a sensory neuron and a
motor neuron to respond to the sensation (pain, heat, stretch).
The correct answer is a—
B. Answer b is incorrect. Relaying messages through the thalamus is not required for
the functioning of a reflex.
The correct answer is a—
C. Answer c is incorrect. Involvement of the cerebral cortex is not required for the
functioning of a reflex. In addition, this answer does not include the sensory
component.
The correct answer is a—
D. Answer d is incorrect. It contains components that are not required for the
functioning of a reflex (cerebral cortex and thalamus) and does not include those
that are required (sensory and motor neurons).
13. As you sit quietly reading this sentence, the part of the nervous system that is
most active is the—
a. somatic nervous system
b. sympathetic nervous system
c. parasympathetic nervous system
d. none of these choices is correct
The correct answer is c—
A. Answer a is incorrect. The somatic nervous system involves movement of the
skeletal muscles, which is unlikely to be prominent as you sit quietly.
The correct answer is c—
B. Answer b is incorrect. The sympathetic nervous system is primarily involved in
threat avoidance (the fight-or-flight response), which is unlikely to be occurring
as you read quietly.
The correct answer is c—parasympathetic nervous system
C. Answer c is correct. The parasympathetic system is in charge of normal body
functions during periods of quiet (rest-and-digest).
The correct answer is c—
D. Answer d is incorrect. The answer “parasympathetic nervous system” is a correct
answer to the question.
14. G protein coupled receptors are involved in the nervous system by—
a. controlling the release of neurotransmitters
b. controlling the opening and closing of Na+ channels during an action
potential
c. controlling the opening and closing of K+ channels during an action
potential
d. acting as receptors for neurotransmitters on postsynaptic cells
The correct answer is c—
A. Answer a is incorrect. The release of neurotransmitters involves Ca2+ signaling,
not G protein–coupled receptors.
The correct answer is c—
B. Answer b is incorrect. Na+ channels involved in action potentials are voltagegated.
The correct answer is c—controlling the opening and closing of K+ channels during an
action potential
C. Answer c is correct. K+ channels involved in action potentials are voltage-gated.
The correct answer is c—
D. Answer d is incorrect. G protein–coupled receptors can act as receptors for
neurotransmitters.
15. During an action potential—
a. the rising phase is due to an influx of Na+
b. the falling phase is due to an influx of K+
c. the falling phase is due to an efflux of K+
d. both a and c
The correct answer is c—
A. Answer a is incorrect.
The correct answer is c—
B. Answer b is incorrect. The rising phase is due to an influx of Na+, not K+.
The correct answer is c—the falling phase is due to an efflux of K+
C. Answer c is incorrect.
The correct answer is c—
D. Answer d is incorrect.
Challenge Questions
+
1. Tetraethylammonium (TEA) is a drug that blocks voltage-gated K channels.
What effect would TEA have on the action potentials produced by a neuron? If
TEA could be applied selectively to a presynaptic neuron that releases an
excitatory neurotransmitter, how would it alter the synaptic effect of that
neurotransmitter on the postsynaptic cell?
+
+
Answer—TEA blocks K channels so that they will not permit the passage of K out of
+
the cell, thereby not allowing the cell to return to the resting potential. Voltage-gated Na
channels would still be functional and Na+ would still flow into the cell but there would
+
be no repolarization. Na would continue to flow into the cell until an electrochemical
+
equilibrium was reached for Na , which is + 60 mV. After the membrane potential
reached + 60 mV, there would be no net movement of Na+, but the membrane would also
not be able to repolarize back to the resting membrane potential. The neuron would no
longer be able to function.
The effects on the postsynaptic cell would be somewhat similar if TEA were applied
to the presynaptic cell. The presynaptic cell would depolarize and would continue to
release neurotransmitter until it had exhausted its store of synaptic vesicles. As a result,
the postsynaptic cell would be bombarded with neurotransmitters and would be
stimulated continuously until the stores of presynaptic neurotransmitter were depleted.
The postsynaptic cell however would recover, being able to repolarize its membrane, and
return to the resting membrane potential.
2. Describe the status of the Na+ and K+ channels at each of the following stages:
rising, falling, and undershoot.
Answer—
Rising: Na+ gates open, K+ closed
Falling: Na+ inactivation gate closes, K+ open
Undershoot: Na+ activation gate closed, inactivation gate open, K+ gate closing
4. Describe the steps required to produce an excitatory postsynaptic potential
(EPSP). How would these differ at an inhibitory synapse?
Answer—
Action potential arrives at the end of the axon.
Ca2+ channels open.
Ca2+ causes synaptic vesicles to fuse with the axon membrane at the synapse.
Synaptic vesicles release their neurotransmitter.
Neurotransmitter molecules diffuse across synaptic cleft.
Postsynaptic receptor proteins bind neurotransmitter.
Postsynaptic membrane depolarizes.
If this were an inhibitory synapse, the binding of receptor protein and neurotransmitter
would cause the postsynaptic membrane to hyperpolarize.
5. Your friend Karen loves caffeine. However, lately she has been complaining that
she needs to drink more caffeinated beverages in order to get the same effect that
she used to. Excellent student of biology that you are, you tell her that this is to
be expected. Why?
Answer—Cells exposed to a stimulus repeatedly may lose their ability to respond. This is
known as habituation. Karen’s postsynaptic cells may have decreased the number of
receptor proteins they produce because the stimulatory signal is so abundant. The result is
that it now takes more stimuli to achieve the same result.