1. Neurons, Synapses, and Signaling
Neurons, Synapses, and Signaling

2. Which combination of axon features should lead an axon to communicate with downstream cells most slowly? An axon that is 1. long. 2. short. 3. wide. 4. thin. 5. myelinated. 6. nonmyelinated.
1, 3, and 5
1, 3, and 6
1, 4, and 6
2, 3, and 5
2, 4, and 6
Answer: c

3. Which combination of axon features should lead an axon to communicate with downstream cells most slowly? An axon that is 1. long. 2. short. 3. wide. 4. thin. 5. myelinated. 6. nonmyelinated.
1, 3, and 5
1, 3, and 6
1, 4, and 6
2, 3, and 5
2, 4, and 6

4. In a typical motor neuron, what is the correct sequence in which these structures usually become involved in transmitting an electrical current? 1. cell body 2. axon 3. axon hillock 4. dendrites 5. synaptic terminals
4, 1, 3, 2, 5
5, 4, 1, 3, 2
4, 3, 1, 2, 5
5, 4, 1, 2, 3
4, 1, 2, 3, 5
Answer: a 4

5. In a typical motor neuron, what is the correct sequence in which these structures usually become involved in transmitting an electrical current? 1. cell body 2. axon 3. axon hillock 4. dendrites 5. synaptic terminals
4, 1, 3, 2, 5
5, 4, 1, 3, 2
4, 3, 1, 2, 5
5, 4, 1, 2, 3
4, 1, 2, 3, 5 5

6. Which gradient(s) is/are directly responsible for producing membrane potentials? 1. concentration gradient 2. pressure gradient 3. partial pressure gradient 4. electrical gradient
1 only
1 and 4
2 and 3
1, 3, and 4
all four
Answer: b 6

7. Which gradient(s) is/are directly responsible for producing membrane potentials? 1. concentration gradient 2. pressure gradient 3. partial pressure gradient 4. electrical gradient
1 only
1 and 4
2 and 3
1, 3, and 4
all four 7

8. How many of these statements about hyperpolarization of a neuron is/are true? When hyperpolarization occurs, 1. membrane potential is more negative than during resting potential. 2. membrane potential is closer to EK than it is to ENa. 3. K+ and/or Cl− channels are open. 4. if it occurs in a downstream neuron, IPSPs are more likely to be generated than are EPSPs. 5. generation of action potentials is less likely to occur.
only one statement
two statements
three statements
four statements
all five statements
Answer: e 8

9. How many of these statements about hyperpolarization of a neuron is/are true? When hyperpolarization occurs, 1. membrane potential is more negative than during resting potential. 2. membrane potential is closer to EK than it is to ENa. 3. K+ and/or Cl− channels are open. 4. if it occurs in a downstream neuron, IPSPs are more likely to be generated than are EPSPs. 5. generation of action potentials is less likely to occur.
only one statement
two statements
three statements
four statements
all five statements 9

10. Resting potential is mostly due to ion movements through which two of the following? 1. Na+/K+ pumps 2. voltage-gated Na+ and K+ channels 3. ligand-gated Na+ and K+ channels 4. voltage-gated Ca2+ channels 5. Na+ and K+ leak channels
1 and 2
1 and 3
1 and 5
2 and 3
4 and 5
Answer: c 10

11. Resting potential is mostly due to ion movements through which two of the following? 1. Na+/K+ pumps 2. voltage-gated Na+ and K+ channels 3. ligand-gated Na+ and K+ channels 4. voltage-gated Ca2+ channels 5. Na+ and K+ leak channels
1 and 2
1 and 3
1 and 5
2 and 3
4 and 5 11

12. What is the correct sequence in which the following events occur, leading to the cessation of acetylcholine (ACh) stimulation of downstream skeletal muscle cells? 1. migration of synaptic vesicles ceases 2. ACh release from presynaptic membrane ceases 3. hydrolysis of last ACh molecules in synaptic cleft and postsynaptic membrane 4. removal of Ca2+ from synaptic terminals 5. action potentials along motor neuron cease
1, 5, 4, 2, 3
5, 1, 4, 2, 3
4, 2, 3, 5, 1
4, 1, 2, 3, 5
5, 4, 1, 2, 3
Answer: e 12

13. What is the correct sequence in which the following events occur, leading to the cessation of acetylcholine (ACh) stimulation of downstream skeletal muscle cells? 1. migration of synaptic vesicles ceases 2. ACh release from presynaptic membrane ceases 3. hydrolysis of last ACh molecules in synaptic cleft and postsynaptic membrane 4. removal of Ca2+ from synaptic terminals 5. action potentials along motor neuron cease
1, 5, 4, 2, 3
5, 1, 4, 2, 3
4, 2, 3, 5, 1
4, 1, 2, 3, 5
5, 4, 1, 2, 3 13

14. If an axon cannot perform saltatory conduction, then what is probably true of this axon?
It has fewer voltage-gated Na+ channels than an axon that can perform saltatory conduction.
It lacks an effective myelin sheath.
It is associated with either Schwann cells or oligodendrocytes.
It has multiple nodes of Ranvier.
It generates fewer action potentials, and requires less ATP, than an axon of equal length that can perform saltatory conduction.
Answer: b 14

15. If an axon cannot perform saltatory conduction, then what is probably true of this axon?
It has fewer voltage-gated Na+ channels than an axon that can perform saltatory conduction.
It lacks an effective myelin sheath.
It is associated with either Schwann cells or oligodendrocytes.
It has multiple nodes of Ranvier.
It generates fewer action potentials, and requires less ATP, than an axon of equal length that can perform saltatory conduction. 15

16. Which is most directly involved in causing neurotransmitter release from the presynaptic membrane?K+
Cl+
Ca2+
large, proteinaceous anions
Answer: d 16

17. Which is most directly involved in causing neurotransmitter release from the presynaptic membrane?K+
Cl+
Ca2+
large, proteinaceous anions 17

18. If a single type of neurotransmitter, released simultaneously by many different neurons onto the same downstream neuron, causes far more K+ channels than Na+ channels to open in this downstream neuron, then which of the following should occur as a result? 1. spatial summation 2. temporal summation 3. depolarization 4. hyperpolarization 5. IPSPs 6. EPSPs
1, 3, and 6
1, 4, and 5
1, 4, and 6
2, 4, and 6
2, 3, and 5
Answer: b 18

19. If a single type of neurotransmitter, released simultaneously by many different neurons onto the same downstream neuron, causes far more K+ channels than Na+ channels to open in this downstream neuron, then which of the following should occur as a result? 1. spatial summation 2. temporal summation 3. depolarization 4. hyperpolarization 5. IPSPs 6. EPSPs
1, 3, and 6
1, 4, and 5
1, 4, and 6
2, 4, and 6
2, 3, and 5 19

20. Which of the following neurotransmitters is incorrectly matched with its definition?
a) acetylcholine—a biogenic amine that affects sleep, mood, attention and learning
b) glutamate—an amino acid and the most common neurotransmitter in the CNS
c) norepinephrine—an excitatory neurotransmitter synthesized from the amino acid tyrosine
d) substance P—a neuropeptide, excitatory neurotransmitter that mediates pain perception
e) nitric oxide—a gaseous neurotransmitter that works like a hormone
Answer: a

21. Which of the following neurotransmitters is incorrectly matched with its definition?
a) acetylcholine—a biogenic amine that affects sleep, mood, attention and learning
b) glutamate—an amino acid and the most common neurotransmitter in the CNS
c) norepinephrine—an excitatory neurotransmitter synthesized from the amino acid tyrosine
d) substance P—a neuropeptide, excitatory neurotransmitter that mediates pain perception
e) nitric oxide—a gaseous neurotransmitter that works like a hormone

22. Scientific Skills Exercises
The data from this experiment are expressed using scientific notation: a numerical factor times a power of 10. Remember that a negative power of 10 means a number less than 1. For example, the concentration 10–1 M (molar) can also be written as 0.1 M.

23. What is the lowest concentration of morphine that blocked naloxone binding, in standard notation?
a)  M
b)  M
c)  M
d)  M
Answer: a

24. What is the lowest concentration of morphine that blocked naloxone binding, in standard notation?
a)  M
b)  M
c)  M
d)  M

25. What result did the researchers obtain for atropine, in standard notation?
no effect at  M
no effect at  M
c) no effect at 0.001 M
d) no effect at 10,000 M
Answer: a

26. What result did the researchers obtain for atropine, in standard notation?
no effect at  M
no effect at  M
c) no effect at 0.001 M
d) no effect at 10,000 M

27. Compare the concentrations for methadone (2 × 10–8 M) and phenobarbital (10–4 M). Which concentration is higher and by how much?
Phenobarbital’s concentration is 2,000 times higher.
b) Phenobarbital’s concentration is 500 times higher.
c) Phenobarbital’s concentration is 5,000 times higher.
d) Methadone’s concentration is 20,000 times higher.
Answer: c

28. Compare the concentrations for methadone (2 × 10–8 M) and phenobarbital (10–4 M). Which concentration is higher and by how much?
Phenobarbital’s concentration is 2,000 times higher.
b) Phenobarbital’s concentration is 500 times higher.
c) Phenobarbital’s concentration is 5,000 times higher.
d) Methadone’s concentration is 20,000 times higher.

29. Which drugs blocked naloxone binding in this experiment?
a) morphine, methadone, and serotonin only
b) morphine, methadone, and levorphanol only
c) morphine, methadone, levorphanol, phenobarbital, atropine, and serotonin
d) morphine and methadone only
Answer: b

30. Which drugs blocked naloxone binding in this experiment?
a) morphine, methadone, and serotonin only
b) morphine, methadone, and levorphanol only
c) morphine, methadone, levorphanol, phenobarbital, atropine, and serotonin
d) morphine and methadone only

31. Would phenobarbital, atropine, or serotonin have blocked naloxone binding at a concentration of 10–5 M?
a) All of these drugs would have blocked naloxone binding at 10–5 M.
It is impossible to tell from the data.
c) None of these drugs would have blocked naloxone binding at 10–5 M.
d) Phenobarbital would have blocked naloxone binding at 10–5 M, but atropine and serotonin would not have.
Answer: c

32. Would phenobarbital, atropine, or serotonin have blocked naloxone binding at a concentration of 10–5 M?
a) All of these drugs would have blocked naloxone binding at 10–5 M.
It is impossible to tell from the data.
c) None of these drugs would have blocked naloxone binding at 10–5 M.
d) Phenobarbital would have blocked naloxone binding at 10–5 M, but atropine and serotonin would not have.

33. Morphine, methadone, and levorphanol blocked naloxone binding in this experiment. What do these results indicate about the brain receptors for naloxone?
a) They are specific for the non-opiate drugs used in the experiment.
b) They are specific for opiate drugs.
They are specific for morphine.
d) They are specific for both opiate and non-opiate drugs.
Answer: b

34. Morphine, methadone, and levorphanol blocked naloxone binding in this experiment. What do these results indicate about the brain receptors for naloxone?
a) They are specific for the non-opiate drugs used in the experiment.
b) They are specific for opiate drugs.
They are specific for morphine.
d) They are specific for both opiate and non-opiate drugs.

35. When the researchers repeated the experiment using tissue from mammalian intestinal muscles rather than brains, they found no naloxone binding. What does this result suggest about opiate receptors in mammalian intestinal muscle tissue?
a) There are no opiate receptors in mammalian intestinal muscle tissue.
b) There may be opiate receptors in mammalian intestinal muscle tissue. Further experiments are needed to be sure.
c) There are opiate receptors in mammalian intestinal muscle tissue.
d) There are no naloxone receptors in mammalian intestinal muscle tissue, but there are opiate receptors.
Answer: a

36. When the researchers repeated the experiment using tissue from mammalian intestinal muscles rather than brains, they found no naloxone binding. What does this result suggest about opiate receptors in mammalian intestinal muscle tissue?
a) There are no opiate receptors in mammalian intestinal muscle tissue.
b) There may be opiate receptors in mammalian intestinal muscle tissue. Further experiments are needed to be sure.
c) There are opiate receptors in mammalian intestinal muscle tissue.
d) There are no naloxone receptors in mammalian intestinal muscle tissue, but there are opiate receptors.