Bio II Chapter 48

59) Of those listed, which event occurs first following a depolarizing stimulus applied to the presynaptic membrane of an axon terminal?

A) Voltage-gated calcium channels in the membrane open.

31) After the depolarization phase of an action potential, the resting potential is restored by ________.

A) the opening of voltage-gated potassium channels and the inactivation of sodium channels

20) Refer to the following graph of an action potential to answer the question. The membrane's permeability to sodium ions is greatest at label ________.

B) B

22) Refer to the following graph of an action potential to answer the question. 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.

B) C

4) Why are action potentials usually conducted in one direction?

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

49) An example of ligand-gated ion channels is ________.

B) acetylcholine receptors at the neuromuscular junction

62) 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?

B) convulsions due to constant muscle stimulation

6) In a simple synapse, neurotransmitter chemicals are received by ________.

B) dendrites

24) 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 ________.

B) hyperpolarization of the neuron

41) 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?

B) immediate loss of action potential with gradual shift of resting potential

16) The Nernst equation specifies the equilibrium potential for a particular ion. This equilibrium potential is a function of ________.

B) ion concentration gradient

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

B) its signals bind to receptor proteins on the muscles

30) Pyrethroid insecticides prevent the voltage-gated sodium channels of insects from inactivating. Neurons that were exposed to pyrethroids would ________.

B) not repolarize during an action potential

32) The "undershoot" phase of hyperpolarization is due to ________.

B) sustained opening of voltage-gated potassium channels

8) The operation of the sodium-potassium pump moves ________.

D) sodium ions out of the cell and potassium ions into the cell

33) The fastest possible conduction velocity of action potentials is observed in ________.

D) thick, myelinated neurons

34) 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 ________.

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

18) Use the information in the table to answer the question. Ion Extracellular concentration (mM) Intracellular concentration (mM) Na+ 300 50 K+ 40 350 Calculate the equilibrium potential for sodium. Assume a temperature of 37°C.

A) +48.2 mV

21) Refer to the following graph of an action potential to answer the question. The minimum graded depolarization needed to operate the voltage-gated sodium and potassium channels is indicated by the label ________.

A) A

15) Which of the following ions is most likely to cross the plasma membrane of a resting neuron?

A) K+

5) 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.

56) The botulinum toxin, which causes botulism, reduces the synaptic release of ________.

A) acetylcholine

57) The heart rate of a vertebrate will decrease in response to the arrival of ________.

A) acetylcholine

27) Conduction and refractory periods (states) are typical of ________.

A) action potentials

46) An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to ________.

A) potassium ions

7) Although the membrane of a "resting" neuron is highly permeable to potassium ions, its membrane potential does not exactly match the equilibrium potential for potassium because the neuronal membrane is also ________.

A) slightly permeable to sodium ions

52) When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron's membrane potential has not returned to the resting potential before the second EPSP arrives, the EPSPs add together producing ________.

A) temporal summation

5) In a simple synapse, neurotransmitter chemicals are released by ________.

A) the presynaptic membrane

35) Why are action potentials usually conducted in one direction?

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

36) 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?

B) The membrane potential would become less negative.

13) If you experimentally increase the concentration of Na+ outside a cell while maintaining other ion concentrations as they were, what would happen to the cell's membrane potential?

B) The membrane potential would become more positive.

40) 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?

B) Unlike the crab, the fish's axons are wrapped in myelin.

45) Acetylcholine released into the junction between a motor neuron and a skeletal muscle binds to a sodium/potassium channel and opens it. This is an example of ________.

B) a ligand-gated channel

51) If excitatory postsynaptic potentials (EPSPs) are produced nearly simultaneously through two different synapses on the same postsynaptic neuron, the EPSPs can also add together creating ________.

B) a spatial summation

43) 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.

B) only II

17) Use the information in the table to answer the question. Ion Extracellular concentration (mM) Intracellular concentration (mM) Na+ 300 50 K+ 40 350 Calculate the equilibrium potential for potassium. Assume a temperature of 37°C.

C) -58.4 mV

47) The following steps refer to various stages in transmission at a chemical synapse. 1. Neurotransmitter binds with receptors associated with the postsynaptic membrane. 2. Calcium ions rush into neuron's cytoplasm. 3. An action potential depolarizes the membrane of the presynaptic axon terminal. 4. The ligand-gated ion channels open. 5. The synaptic vesicles release neurotransmitter into the synaptic cleft. Which sequence of events is correct?

C) 3 → 2 → 5 → 1 → 4

37) Which of the following statements about action potentials is correct?

C) Action potentials are propagated down the length of the axon.

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

C) Disruption to the normal "resting" distribution of potassium and sodium ions.

60) How could you increase the magnitude of excitatory postsynaptic potentials (EPSPs) generated at a synapse?

C) Increase Na+ permeability.

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

C) No action potential results.

1) What happens when a resting neuron's membrane depolarizes?

C) The neuron's membrane voltage becomes more positive.

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

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

12) Two fundamental concepts about the ion channels of a "resting" neuron are that the channels ________.

C) are open or closed depending on their type, and are specific as to which ion can traverse them

2) A common feature of action potentials is that they

C) are triggered by a depolarization that reaches threshold.

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

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

11) The membrane potential in which there is no net movement of the ion across the membrane is called the ________.

C) equilibrium potential

25) Opening all of the sodium channels on an otherwise typical neuron, with all other ion channels closed (which is an admittedly artificial setting), should move its membrane potential to ________.

C) equilibrium potential for sodium

2) Most of the neurons in the human central nervous system are ________.

C) interneurons

28) The "threshold" potential of a membrane is the ________.

C) minimum depolarization needed to operate the voltage-gated sodium and potassium channels

29) Action potentials move along axons ________.

C) more rapidly in myelinated than in unmyelinated axons

58) A chemical that affects neuronal function but is not stored in presynaptic vesicles is ________.

C) nitric oxide

42) Which of the following will increase the speed of an action potential moving down an axon? I) Action potentials move faster in wider axons. II) Action potentials move faster in axons lacking potassium ion channels. III) Action potentials move faster in myelinated axons.

C) only I and III

53) One-way synaptic transmission occurs because ________.

C) receptors for neurotransmitters are mostly found on the postsynaptic membrane

14) The concentrations of ions are very different inside and outside a nerve cell due to ________.

C) sodium-potassium pumps

4) The point of connection between two communicating neurons is called the ________.

C) synapse

3) Where are neurotransmitter receptors located?

C) the postsynaptic membrane

19) Refer to the following graph of an action potential to answer the question. The membrane potential is closest to the equilibrium potential for potassium at label ________.

D) D

23) Refer to the following graph of an action potential to answer the question. The neuronal membrane is at its resting potential at label ________.

D) E

54) Neurotransmitters can affect postsynaptic cells by ________. I) initiating signal transduction pathways in the cells II) causing molecular changes in the cells III) altering ion channel proteins IV) altering the permeability of the cells

D) I, II, III, and IV

10) In a resting potential, an example of a cation that is more abundant as a solute in the cytosol of a neuron than it is in the interstitial fluid outside the neuron is ________.

D) K+

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

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

48) The activity of acetylcholine in a synapse is terminated by its ________.

D) degradation on the postsynaptic membrane

44) Neurotransmitters are released from axon terminals via ________.

D) exocytosis

55) The amino acid that operates at most inhibitory synapses in the brain is ________.

D) gamma-aminobutyric acid (GABA)

50) Neurotransmitters categorized as inhibitory are expected to ________.

D) hyperpolarize the membrane

26) A graded hyperpolarization of a membrane can be induced by ________.

D) increasing its membrane's permeability to K+

1) The three stages of information processing in animals include ________.

D) sensory reception, an integrating center, and effectors (motor neurons)