Chapter 48 Questions

Question 1

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that __________.

a. the threshold value in the postsynaptic membrane is different for cell X and cell Y
b. the axon of cell X is myelinated, but that of cell Y is not
c. only cell Y produces an enzyme that terminates the activity of the neurotransmitter
d. cells X and Y express different receptor molecules for this particular neurotransmitter

Answer 1

d. cells X and Y express different receptor molecules for this particular neurotransmitter

Question 2

Gated ion channels

a. open and close in response to a stimulus.
b. are found only on vesicles.
c. require ATP hydrolysis.
d. move molecules against an electrochemical gradient.

Answer 2

a. open and close in response to a stimulus.

Question 3

The sodium-potassium pump in the plasma membrane of cells

a. uses chemical energy to generate chemical gradients.
b. transports Na+ and K+ out of the cell.
c. converts ADP and Pi to ATP.
d. carries out a direct exchange of Na+ and K+.

Answer 3

a. uses chemical energy to generate chemical gradients.

Question 4

In exocytosis, dissolved materials move from fluid

a. in the cytoplasm to fluid in the nucleus.
b. in the Golgi apparatus to fluid in the endoplasmic reticulum.
c. in vesicles to fluid outside of cells.
d. in lysosomes to the cytosol.

Answer 4

c. in vesicles to fluid outside of cells.

Question 5

Choose the set that includes the most charged compounds that are more abundant inside neurons, in the cytosol, than outside the neurons, in the extracellular fluid.

a. potassium ions and proteins
b. chloride ions and proteins
c. proteins and sodium ions
d. sodium and chloride ions
e. sodium and potassium ions

Answer 5

a. potassium ions and proteins

Question 6

Ions move in the direction opposite to that favored by the chemical concentration gradient when _____.

a. proteins leak out of a neuron
b. simple diffusion operates after active transport has been permanently halted by being poisoned
c. potassium ions exit the neuron during the repolarization phase of an action potential
d. sodium ions enter a neuron during the depolarization phase of an action potential
e. they are pumped by proteins that require ATP hydrolysis and when the electrical charge gradient repulses or attracts them

Answer 6

e. they are pumped by proteins that require ATP hydrolysis and when the electrical charge gradient repulses or attracts them

Question 7

In a neuron, during the depolarization phase that may trigger an action potential _____.

a. some voltage-gated sodium channels are open
b. most voltage-gated sodium channels become inactivated
c. most voltage-gated sodium and potassium channels are open
d. most voltage-gated potassium channels are open
e. most voltage-gated sodium channels are open

Answer 7

a. some voltage-gated sodium channels are open

Question 8

The simultaneous arrival of graded depolarization and a graded hyperpolarization of equal but opposite magnitude at a particular location on the dendritic membrane is likely to _____.

a. cause the apoptosis of the neuron
b. cancel each other out, making it appear as if there was no change in membrane potential
c. cause depolarization, because graded depolarizations are more important to neuron function
d. cause hyperpolarization, because graded hyperpolarizations are more important to neuron function
e. allow only the entry of sodium ions into the neuron, and prevent potassium ions from exiting the neuron

Answer 8

b. cancel each other out, making it appear as if there was no change in membrane potential

Question 9

Select the choice that describes neurons with the fastest conduction velocity for action potentials.

a. thin, nonmyelinated neurons
b. thin, myelinated neurons
c. thick, myelinated neurons
d. thick, nonmyelinated neurons
e. All of these choices conduct action potentials at the same velocity.

Answer 9

c. thick, myelinated neurons

Question 10

Of these choices, neuronal communication between the brain and the muscles of the leg is best conceptualized as _____.

a. the transcription of genes
b. electrical signaling
c. the transcription and translation of genes
d. chemical signaling
e. electrical and chemical signaling

Answer 10

e. electrical and chemical signaling

Question 11

A nerve poison that blocks acetylcholine receptors on dendrites would _____.

a. inactivate acetylcholinesterase, allowing acetylcholine to persist in the synapse
b. cause continued stimulation of the postsynaptic membrane
c. reduce the binding of acetylcholine to its receptors on the postsynpatic membrane
d. inhibit the regeneration of acetylcholine for use by the presynaptic terminals
e. cause an immediate and enduring depolarization

Answer 11

c. reduce the binding of acetylcholine to its receptors on the postsynpatic membrane

Question 12

At the neuromuscular junction, the arrival of acetylcholine on the muscle most immediately causes _____.

a. an inhibitory postsynaptic potential
b. a graded depolarization
c. the release of second messengers, such as cAMP
d. a single action potential
e. a graded hyperpolarization

Answer 12

b. a graded depolarization

Question 13

Acetylcholine receptors on skeletal muscles are described as being “ionotropic” receptors because _____.

a. these receptors have a corequisite binding of magnesium ions in order to function
b. binding of acetylcholine to its receptor triggers release of a second messenger, e.g., cAMP, inside the muscle
c. binding of acetylcholine to the receptor protein converts the protein to an open ion channel
d. acetylcholine is an excitatory stimulus to the muscle
e. the receptors ionize as a result of binding acetylcholine, and this directly alters membrane potentials

Answer 13

c. binding of acetylcholine to the receptor protein converts the protein to an open ion channel

Question 14

What happens when a resting neuron’s membrane depolarizes?

a. The equilibrium potential for K+ (E K) becomes more positive.
b. The neuron is less likely to generate an action potential.
c. The neuron’s membrane voltage becomes more positive.
d. There is a net diffusion of Na+ out of the cell.
e. The cell’s inside is more negative than the outside.

Answer 14

c. The neuron’s membrane voltage becomes more positive.

Question 15

A common feature of action potentials is that they

a. require the diffusion of Na+ and K+ through ligand-gated channels to propagate.
b. move at the same speed along all axons.
c. are triggered by a depolarization that reaches the threshold.
d. cause the membrane to hyperpolarize and then depolarize.
e. can undergo temporal and spatial summation.

Answer 15

c. are triggered by a depolarization that reaches the threshold.

Question 16

Where are neurotransmitter receptors located?

a. the postsynaptic membrane
b. the myelin sheath
c. synaptic vesicle membranes
d. the nuclear membrane
e. the nodes of Ranvier

Answer 16

a. the postsynaptic membrane

Question 17

Why are action potentials usually conducted in one direction?

a. Voltage-gated channels for both Na+ and K+ open in only one direction.
b. Ions can flow along the axon in only one direction.
c. The nodes of Ranvier conduct potentials in one direction.
d. The axon hillock has a higher membrane potential than the terminals of the axon.
e. The brief refractory period prevents reopening of voltage-gated Na+ channels.

Answer 17

e. The brief refractory period prevents reopening of voltage-gated Na+ channels.

Question 18

Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal?

a. Synaptic vesicles fuse with the membrane.
b. Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.
c. An EPSP or IPSP is generated in the postsynaptic cell.
d. Voltage-gated calcium channels in the membrane open.
e. The postsynaptic cell produces an action potential.

Answer 18

d. Voltage-gated calcium channels in the membrane open.

Question 19

Identify the correct statement(s) about the resting membrane potential of a cell.
Select all that apply.
a. Concentration gradients of potassium (K+) and sodium (Na+) across the plasma membrane represent potential energy.
b. Neurons are the only cells that have a charge difference across their membranes.
c. Potassium (K+) and sodium (Na+) gradients are maintained by active transport in a resting mammalian neuron.

Answer 19

a. Concentration gradients of potassium (K+) and sodium (Na+) across the plasma membrane represent potential energy.
c. Potassium (K+) and sodium (Na+) gradients are maintained by active transport in a resting mammalian neuron.

Question 20

If the membrane potential of a neuron decreases, the membrane potential _____.

a. becomes more negative.
b. remains unchanged.
c. becomes less negative.

Answer 20

c. becomes less negative.

Question 21

Why is an action potential an all-or-none response to stimuli?

a. Because voltage-gated ion channels open when membrane potential passes a particular level
b. Because a typical neuron receives signals through multiple dendrites but transmits signals through a single axon
c. Because neurons contain gated ion channels that are either open or closed

Answer 21

a. Because voltage-gated ion channels open when membrane potential passes a particular level

Question 22

The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels?

a. Membrane depolarization first opens sodium channels and then opens potassium channels.
b. Membrane depolarization opens sodium channels but closes potassium channels.
c. Membrane depolarization opens sodium and potassium channels at the same time.

Answer 22

a. Membrane depolarization first opens sodium channels and then opens potassium channels.

Question 23

What causes the falling phase of the action potential? Select the best answer.

a. The opening of voltage-gated sodium channels
b. The opening of voltage-gated potassium channels
c. Inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels

Answer 23

c. Inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels

Question 24

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
   a. 1, 3, and 5
   b. 1, 3, and 6
   c. 1, 4, and 6
   d. 2, 3, and 5
   e. 2, 4, and 6

Answer 24

c. 1, 4, and 6

Question 25

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
   a. 4, 1, 3, 2, 5
   b. 5, 4, 1, 3, 2
   c. 4, 3, 1, 2, 5
   d. 5, 4, 1, 2, 3
   e. 4, 1, 2, 3, 5

Answer 25

a. 4, 1, 3, 2, 5

Question 26

Which gradient(s) is/are directly responsible for producing membrane potentials?

1. concentration gradient
2. pressure gradient 3. partial pressure gradient
3. electrical gradient
   a. 1 only
   b. 1 and 4
   c. 2 and 3
   d. 1, 3, and 4
   e. all four

Answer 26

b. 1 and 4

Question 27

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
   a. 1 and 2
   b. 1 and 3
   c. 1 and 5
   d. 2 and 3
   e. 4 and 5

Answer 27

c. 1 and 5

Question 28

If an axon cannot perform saltatory conduction, then what is probably true of this axon?

a. It has fewer voltage-gated Na+ channels than an axon that can perform saltatory conduction.
b. It lacks an effective myelin sheath.
c. It is associated with either Schwann cells or oligodendrocytes.
d. It has multiple nodes of Ranvier.
e. It generates fewer action potentials, and requires less ATP, than an axon of equal length that can perform saltatory conduction.

Answer 28

b. It lacks an effective myelin sheath.

Question 29

Which is most directly involved in causing neurotransmitter release from the presynaptic membrane?

a. Na+
b. K+
c. Cl+
d. Ca2+
e. large, proteinaceous anions

Answer 29

d. Ca2+

Question 30

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
3. hyperpolarization
4. IPSPs
5. EPSPs
   a. 1, 3, and 6
   b. 1, 4, and 5
   c. 1, 4, and 6
   d. 2, 4, and 6
   e. 2, 3, and 5

Answer 30

b. 1, 4, and 5

Question 31

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 31

a. acetylcholine—a biogenic amine that affects sleep, mood, attention, and learning

Question 32

Which statement below best explains why ion movement through channels generates a membrane potential but ion movement generated by the Na+/K+ pump does not?

a. The concentration of K+ is higher inside the cell, while the concentration of Na+ is higher outside.
b. The slow action of the pump creates a small change in the membrane potential.
c. Ions move rapidly through ion channels, specialized pores in the membrane that allow ions to diffuse back and forth, carrying charge.
d. The net movement of positive or negative charge generates a membrane potential.
e. The Na+/K+ pump carries ions against their concentration gradients.

Answer 32

c. Ions move rapidly through ion channels, specialized pores in the membrane that allow ions to diffuse back and forth, carrying charge.

Question 33

In the autoimmune disease myasthenia gravis (MG), the body makes self-reactive antibodies against the acetylcholine receptor on the postsynaptic cell, which block or destroy the receptor. A functional receptor binds acetylcholine, opening an ion channel and producing an EPSP, but this doesn’t happen in MG, which decreases the likelihood of the muscle fiber reaching threshold depolarization and contracting, causing muscle weakness. Which of the following treatments would produce additional muscle strength in a person with MG?

a. treatment with an acetylcholinesterase inhibitor
b. treatment with an antibody to acetylcholine
c. treatment with acetylcholinesterase
d. treatment with a Na+/K+ ATPase inhibitor
e. treatment with an inhibitory neurotransmitter

Answer 33

a. treatment with an acetylcholinesterase inhibitor

Question 34

Which statement correctly describes a difference between ionotropic and metabotropic receptors?

a. Ionotropic receptors act through secondary messengers.
b. Only ionotropic receptors are membrane proteins.
c. Ionotropic receptors are directly linked and metabotropic receptors are indirectly linked to ion channels.
d. Neurotransmitters are only involved with ionotropic receptors.
e. Ionotropic receptors act slowly, while metabotropic act quickly.

Answer 34

c. Ionotropic receptors are directly linked and metabotropic receptors are indirectly linked to ion channels.

Question 35

Botulin toxin prevents the release of what chemical that initiates the signal for muscle contraction?

a. acetylcholine
b. dopamine
c. norepinephrine
d. phosphatidylcholine
e. serotonin

Answer 35

a. acetylcholine

Question 36

In an experiment, the membrane potential of a neuron is hyperpolarized to –120 mV. When an inhibitory neurotransmitter is applied to the preparation, the membrane is depolarized. Which of the following could explain this result?

a. Inhibitory transmitters normally depolarize the synaptic membrane.
b. The normal response of the postsynaptic membrane to any transmitter is depolarization.
c. The inhibitory transmitter activates ligand-gated potassium channels.
d. Sodium channels become inactivated.
e. Calcium channels become activated.

Answer 36

c. The inhibitory transmitter activates ligand-gated potassium channels.

Question 37

The pufferfish toxin, tetrodotoxin (TTX), binds to voltage-gated sodium ion channels and blocks their function. A couple of bites of a poorly cooked pufferfish would cause _____.

a. an increase in the firing of action potentials
b. the prolongation of action potential duration
c. hyperpolarization of nerve cells
d. the inability of cells to depolarize

Answer 37

d. the inability of cells to depolarize

Question 38

Most of the neurons in the human central nervous system are ___.

a. motor neurons
b. interneurons
c. sensory neurons
d. peripheral neurons

Answer 38

b. interneurons

Question 39

The motor (somatic nervous) system can alter the activities of its targets, the skeletal muscle fibers, because ___.

a. it is connected to the internal neural network of the muscles
b. it is electrically coupled by gap junctions to the muscles
c. its signals reach the muscles via the blood
d. its signals bind to receptor proteins on the muscles

Answer 39

d. its signals bind to receptor proteins on the muscles

Question 40

A researcher uses the chemical inhibitor cyanide to reduce ATP production in a neuron. What would be one effect of preventing ATP production?

a. The membrane would become more permeable to sodium.
b. Disruption to the normal “resting” distribution of potassium and sodium ions.
c. A physical breakdown of the plasma membrane would occur.
d. The sodium and potassium channels would all be closed.

Answer 40

b. Disruption to the normal “resting” distribution of potassium and sodium ions.

Question 41

Refer to the following graph of an action potential to answer the question.
Graph.
At label ___, the cell is not hyperpolarized; however, repolarization is in progress, as the sodium channels are inactivated or becoming inactivated, and many potassium channels have opened.
a. B
b. C
c. D
d. E

Answer 41

b. C

Question 42

For a neuron with an initial membrane potential at -70 mV, an increase in the movement of potassium ions out of that neuron’s cytoplasm would result in the ___.

a. replacement of potassium ions with sodium ions
b. replacement of potassium ions with calcium ions
c. depolarization of the neuron
d. hyperpolarization of the neuron

Answer 42

d. hyperpolarization of the neuron

Question 43

Pyrethroid insecticides prevents the voltage-gated sodium channels of insects from inactivating. Neurons that were exposed to pyrethroids would ___.

a. not release neurotransmitter molecules
b. not be able to open potassium channels
c. not repolarize during an action potential
d. become hyperpolarized during an action potential

Answer 43

c. not repolarize during an action potential

Question 44

Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. If you experimentally depolarize the middle of the axon to threshold, using an electronic probe, then ___.

a. an action potential will be initiated and proceed only back toward the axon hillock
b. an action potential will be initiated and proceed only in the normal direction toward the axon terminal
c. two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock
d. no action potential will be initiated

Answer 44

c. two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock

Question 45

Why are action potentials usually conducted in one direction?

a. The axon hillock has a higher membrane potential than the terminals of the axon.
b. The nodes of Ranvier conduct potentials in one direction.
c. The brief refractory period prevents reopening of voltage-gated sodium channels.
d. Voltage-gated channels for both Na+ and K+ open in only one direction.

Answer 45

c. The brief refractory period prevents reopening of voltage-gated sodium channels.

Question 46

If you experimentally increase the concentration of K+ inside a cell while maintaining other ion concentrations as they were, what would happen to the cell’s membrane potential?

a. The membrane potential would remain the same.
b. The membrane potential would become more negative.
c. The membrane potential would become less negative.
d. The membrane potential would first become more negative and then less negative.

Answer 46

c. The membrane potential would become less negative.

Question 47

Which of the following statements about action potentials is correct?

a. Action potentials for a given neuron vary in magnitude.
b. Action potentials for a given neuron vary in duration.
c. Movement of ions during the action potential occurs mostly through the sodium pump.
d. Action potentials are propagated down the length of the axon.

Answer 47

d. Action potentials are propagated down the length of the axon.

Question 48

Why do Na+ ions enter the cell when voltage-gated Na+ channels are opened in neurons?

a. because the Na+ ions are actively transported by the sodium-potassium pump into the cell
b. because the Na+ concentration is much lower outside the cell than it is inside
c. because the Na+ concentration is much higher outside the cell than it is inside, and the Na+ ions are attracted to the negatively charged interior
d. because the Na+ concentration is much higher outside the cell than it is inside, and the Na+ ions are actively transported by the sodium-potassium pump into the cell

Answer 48

c. because the Na+ concentration is much higher outside the cell than it is inside, and the Na+ ions are attracted to the negatively charged interior

Question 49

What would probably happen if a long neuron had one continuous myelin sheath down the length of the axon with no nodes of Ranvier?

a. There could be no action potential generated at the axon hillock.
b. Only potassium could move across the membrane, but not sodium.
c. The action potential would be propagated nearly instantaneously to the synapse.
d. The signal would fade because it is not renewed by the opening of more sodium channels.

Answer 49

d. The signal would fade because it is not renewed by the opening of more sodium channels.

Question 50

A neurophysiologist is investigating nerve reflexes in two different animals: a crab and a fish. Action potentials are found to pass more rapidly along the fish’s neurons. What is the most likely explanation?

a. Unlike the crab, the fish’s axons are wrapped in myelin, and the fish’s axons are smaller in diameter; small axons transmit action potentials faster than large axons do.
b. The fish’s axons are smaller in diameter; small axons transmit action potentials faster than large axons do.
c. There are more ion channels in the axons of the crab compared with fish axons.
d. Unlike the crab, the fish’s axons are wrapped in myelin.

Answer 50

d. Unlike the crab, the fish’s axons are wrapped in myelin.

Question 51

Tetrodotoxin blocks voltage-gated sodium channels, and ouabain blocks sodium-potassium pumps. If you added both tetrodotoxin and ouabain to a solution containing neural tissue, what responses would you expect?

a. slow decrease of resting potential and action potential amplitudes
b. immediate loss of action potential with gradual shift of resting potential
c. immediate loss of resting potential
d. No effect; the substances counteract each other.

Answer 51

b. immediate loss of action potential with gradual shift of resting potential

Question 52

In multiple sclerosis, the myelin sheaths around the axons of the brain and spinal cord are damaged and demyelination results. How does this disease manifest at the level of the action potential?
I. Action potentials move in the opposite direction on the axon.
II. Action potentials move more slowly along the axon.
III. No action potentials are transmitted.
a. only I
b. only II
c. only III
d. only II and III

Answer 52

b. only II

Question 53

Neurotransmitters are released from axon terminals via ___.

a. osmosis
b. exocytosis
c. diffusion
d. active transport

Answer 53

b. exocytosis

Question 54

Neurotransmitters categorized as inhibitory are expected to ____.

a. open sodium channels
b. close potassium channels
c. act independently of their receptor proteins
d. hyperpolarize the membrane

Answer 54

d. hyperpolarize the membrane

Question 55

One-way synaptic transmission occurs because ___.

a. more receptors for neurotransmitters are found on the presynaptic membrane
b. the postsynaptic cell contains most of the synaptic vesicles
c. receptors for neurotransmitters are mostly found on the postsynaptic membrane
d. only dendrites can respond to electrical signals

Answer 55

c. receptors for neurotransmitters are mostly found on the postsynaptic membrane

Question 56

What happens if twice as many inhibitory postsynaptic potentials (IPSPs) as excitatory postsynaptic potentials (EPSPs) arrive in close proximity at a postsynaptic neuron?

a. Many action potentials result.
b. A stronger action potential results.
c. A weaker action potential results.
d. No action potential results.

Answer 56

d. No action potential results.

Question 57

At the neuromuscular junction, the neurotransmitter acetylcholine (ACh) is degraded by acetylcholinesterase. If a neurophysiologist applies the naturally occurring acetylcholinesterase inhibitor, onchidal (produced by the mollusc Onchidella binneyi), to a synapse, what would you expect to happen?

a. convulsions due to constant muscle stimulation
b. decrease in the frequency of action potentials
c. no effect
d. paralysis of muscle tissue

Answer 57

a. convulsions due to constant muscle stimulation

Question 58

What happens when a resting neuron’s membrane depolarizes?

a. There is a net diffusion of Na+ out of the cell.
b. The equilibrium potential for K+(EK) becomes more positive.
c. The neuron’s membrane voltage becomes more positive.
d. The cell’s inside is more negative than the outside.

Answer 58

c. The neuron’s membrane voltage becomes more positive.

Question 59

A common feature of action potentials is that they

a. cause the membrane to hyperpolarize and then depolarize.
b. can undergo temporal and spatial summation.
c. are triggered by a depolarization that reaches threshold.
d. move at the same speed along all axons.

Answer 59

c. are triggered by a depolarization that reaches threshold.

Question 60

Where are neurotransmitter receptors located?

a. the nuclear membrane
b. the nodes of Ranvier
c. the postsynaptic membrane
d. synaptic vesicle membranes

Answer 60

c. the postsynaptic membrane

Question 61

Why are action potentials usually conducted in one direction?

a. Ions can flow along the axon in only one direction.
b. The brief refractory period prevents reopening of voltage-gated Na+ channels.
c. The axon hillock has a higher membrane potential than the terminals of the axon.
d. Voltage-gated channels for both Na+ and K+ open in only one direction.

Answer 61

b. The brief refractory period prevents reopening of voltage-gated Na+ channels.

Question 62

Which of the following is the most direct result of depolarizing the presynaptic membrane of an axon terminal?

a. Voltage-gated calcium channels in the membrane open.
b. Synaptic vesicles fuse with the membrane.
c. Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.
d. An EPSP or IPSP is generated in the postsynaptic cell.

Answer 62

a. Voltage-gated calcium channels in the membrane open.

Question 63

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that

a. the threshold value in the postsynaptic membrane is different for cell X and cell Y.
b. the axon of cell X is myelinated, but that of cell Y is not.
c. only cell Y produces an enzyme that terminates the activity of the neurotransmitter.
d. cells X and Y express different receptor molecules for this particular neurotransmitter.

Answer 63

d. cells X and Y express different receptor molecules for this particular neurotransmitter.