Ch. 11 pt.2
104) The porcupinefish produces a toxin that binds voltage-gated sodium channels. Determine the effect of the toxin on nerve function.
The axon of the neuron would be unable to generate action potentials. The activation of voltage-gated sodium channels is critical for the influx of sodium ions into the cell along their electrochemical gradient. Depolarization is dependent upon the influx of sodium ions (to about +30 mV).
109) A postsynaptic neuron is bombarded by synaptic inputs from several hundred presynaptic neurons. However, this neuron does not appear to transmit an impulse. Propose an explanation of why this could occur.
The input from each presynaptic neuron may be either excitatory or inhibitory. The postsynaptic neuron integrates this information into a single effect known as neural integration. In this situation, the IPSPs outnumber the EPSPs, and the neuron is inhibited from generating an action potential. The numerous IPSPs hyperpolarize the postsynaptic neuron.
103) Discuss the two main factors involved in the generation of a neuron's resting membrane potential.
The main factor is the ease at which potassium ions cross the membrane and cause a net loss of positive ions from the cytosol. The cytosol constantly loses more positive charges than it gains, leading to the negative value of the resting membrane potential. The second factor, the Na+/K+ pump, maintains a sodium gradient and a potassium gradient by moving two potassium ions into the cytosol as it moves three sodium ions into the extracellular fluid.
46) During saltatory conduction, action potentials are generated: A) only at nodes of Ranvier of myelinated axons. B) along the entire length of the unmyelinated axon. C) regardless if threshold is reached. D) when the entire axolemma is depolarized
a
47) Determine the fiber type in which propagation of an action potential will occur most quickly. A) myelinated type A fiber B) unmyelinated type B fiber C) myelinated type B fiber D) type C fiber
a
48) Which type of fiber has the largest diameter? A) type A B) type B C) type C D) type D
a
50) The presence of a synaptic cleft between cells is characteristic of: A) chemical synapse. B) electrical synapse. C) both chemical and electrical synapses. D) neither chemical nor electrical synapses
a
52) What is NOT associated with a chemical synapse? A) gap junction B) presynaptic neuron C) synaptic cleft D) neurotransmitter
a
53) What type of synapse must have receptors to transmit signals? A) chemical synapse B) electrical synapse C) both chemical and electrical synapses D) neither chemical nor electrical synapses
a
55) If the receptor site for a neurotransmitter were completely blocked: A) synaptic transmission would fail. B) a weaker action potential would result. C) neurotransmitter release would stop. D) the presynaptic neuron would release a different neurotransmitter.
a
57) Which of the following is most likely to produce an action potential? A) excitatory postsynaptic potential (EPSP) B) opening of potassium ion channels C) inhibitory postsynaptic potential (IPSP) D) hyperpolarization
a
58) What would most likely lead to an IPSP? A) opening of potassium ion channels B) opening of calcium ion channels C) opening of sodium ion channels D) closure of chloride ion channels
a
60) Which of the following would NOT terminate the effects of the neurotransmitter? A) presence of calcium ions in the presynaptic neuron B) reuptake of neurotransmitter into the presynaptic neuron C) degradation of the neurotransmitter by enzymes D) diffusion of the neurotransmitter into the extracellular fluid
a
63) The same ________ can have different effects depending on the properties of the ________. A) neurotransmitter; receptor B) hormone; neurotransmitter C) receptor; neurotransmitter D) substrate; enzyme
a
65) Cholinergic synapses use the neurotransmitter: A) acetylcholine. B) serotonin. C) norepinephrine. D) epinephrine.
a
69) Where are neuronal pools located? A) within the CNS B) within ganglia C) within the PNS D) within nerves
a
38) During repolarization of a neuron: A) sodium ions move out of the cell. B) potassium ions move out of the cell. C) sodium ions move into the cell. D) potassium ions move into the cell.
b
40) Place these steps of the action potential in the correct order. 1. Sodium ions channels return to the resting state and repolarization continues. 2. Voltage-gated sodium ion channels activate, sodium ions enter, and the axon section depolarizes. 3. As potassium ion channels return to resting state, the axolemma may hyperpolarize before returning to the resting membrane potential. 4. A local potential depolarizes the axolemma of the trigger zone to threshold. 5. Sodium ion channels inactivate, and voltage-gated potassium ion channels activate, so sodium ions stop entering and potassium ions leave, beginning repolarization. A) 4, 2, 3, 5, 1 B) 4, 2, 5, 1, 3 C) 4, 2, 1, 3, 5 D) 2, 4, 5, 1, 3
b
41) Which number on the graph represents when voltage-gated sodium channels are open? A) 1 B) 2 C) 3 D) 4
b
51) A neuron that receives neurotransmitters from another neuron is called: A) the presynaptic neuron. B) the postsynaptic neuron. C) an oligodendrocyte. D) a Schwann cell.
b
54) What ion triggers synaptic vesicles to release neurotransmitters into the synaptic cleft? A) sodium B) calcium C) magnesium D) chlorine
b
56) Which of the following must happen first in the order events at a chemical synapse? A) Ion channels respond to the neurotransmitter and lead to a local potential, or possibly an action potential. B) Calcium ion channels in the axon terminal open. C) Calcium ions cause synaptic vesicles to release neurotransmitters into the synaptic cleft. D) Neurotransmitter binds to receptors on the postsynaptic neuron.
b
61) When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what results? A) spatial summation B) temporal summation C) hyperpolarization D) inhibition of the impulse
b
64) Neurotransmitters that bind ionotropic receptors control: A) the formation of a second messenger inside the postsynaptic neuron. B) the movement of ions into or out of the postsynaptic neuron. C) the activation of G-proteins inside the postsynaptic neuron. D) some metabolic process inside the postsynaptic neuron
b
67) Which of the following is the most important excitatory neurotransmitter in the CNS? A) dopamine B) glutamate C) glycine D) GABA
b
68) Which neuropeptide neurotransmitter is released from fibers transmitting sensory information about pain and temperature? A) endorphin B) substance P C) neuropeptide Y D) opioids
b
25) Which of the following is the primary factor in the maintenance of a negative charge during resting membrane potential? A) ligand-gated channels B) voltage-gated channels C) leak channels D) sodium-potassium pump
c
27) What channels open or close in response to physical distortion of the membrane surface, such as vibrations or pressure? A) voltage-gated B) chemically-gated C) mechanically-gated D) ligand-gated
c
29) If a resting axon increases its permeability to sodium ions: A) the membrane potential will repolarize. B) the membrane potential will hyperpolarize. C) the influx of sodium ions will increase and the membrane will depolarize. D) the outward movement of sodium ions will decrease.
c
30) The influx of positive charges makes the membrane potential more positive and is known as: A) polarization. B) repolarization. C) depolarization. D) hyperpolarization.
c
31) A series of measurements with a voltmeter show a neuron's membrane potential becoming more negative, from -70 mV to -85 mV. This neuron is experiencing a: A) depolarization phase. B) repolarization phase. C) hyperpolarization phase. D) polarization phase.
c
32) Graded potentials: A) produce an effect that increases with distance from the point of stimulation. B) produce an effect that spreads actively across the membrane surface. C) may cause either a depolarization or a hyperpolarization. D) cause repolarization.
c
36) What membrane potential must generally be met in order to achieve threshold? A) -85 mV B) -70 mV C) -55 mV D) -30 mV
c
45) When is the generation of an action potential impossible, no matter the strength of the stimulus? A) depolarization B) threshold C) absolute refractory period D) relative refractory period
c
49) The majority of synapses in the nervous system are: A) electrical. B) voltage. C) chemical. D) mechanical.
c
62) Summation that results from the cumulative effect of multiple synapses at multiple places on the neuron is designated: A) temporal summation. B) hyperpolarization. C) spatial summation. D) impulse transmission.
c
66) After acetylcholinesterase (AChE) acts, the presynaptic neuron: A) reabsorbs acetylcholine. B) reabsorbs the acetate. C) reabsorbs the choline. D) reabsorbs synaptic vesicles.
c
71) What best describes a converging circuit? A) One neuron communicates with multiple parts of the brain. B) One axon of an input neuron branches to make contact with multiple postsynaptic neurons. C) Axon terminals from multiple input neurons join onto a single postsynaptic neuron. D) An increasing number of neurons are excited down the pathway of the circuit.
c
35) Which statement best describes the all-or-none principle? A) Local, or graded, potentials will always become action potentials. B) All voltage-gated sodium channels will open or none will open. C) All neurons conduct an action potential together, or none do. D) An action potential happens completely, or it doesn't happen at all.
d
37) Which of the following is correct about threshold? A) Voltage-gated potassium channels inactivate. B) Voltage-gated potassium channels begin to close. C) The membrane begins to hyperpolarize. D) Threshold is more positive than the resting potential.
d
42) Which area on the graph shows when the neuron is in the refractory period? A) 1 B) 2 C) 3 D) 4
d
43) Determine the membrane potential (mV) during the relative refractory period. A) -85 mV B) -55 mV C) +15 mV D) +30 mV
d
44) Voltage-gated sodium channels are activated: A) after voltage-gated potassium channels are activated. B) during repolarization. C) during hyperpolarization. D) only if the cell is depolarized to threshold.
d
59) A local hyperpolarization that changes a postsynaptic neuron's membrane from resting potential to -85 mV is: A) a temporal stimulus. B) an excitatory postsynaptic potential (EPSP). C) a saltatory stimulus. D) an inhibitory postsynaptic potential (IPSP).
d
70) Neuronal pools are collections of: A) bipolar neurons. B) motor neurons. C) efferent neurons. D) interneurons.
d
88) The membrane potential moves from -70 mV to -60 mV
depolarization
90) Sodium ion channels open causing the membrane potential to become more positive
depolarization
93) The membrane potential of the postsynaptic neuron moves closer to threshold during an excitatory postsynaptic potential (EPSP)
depolarization
95) A strong local potential moves the membrane potential to -55 mV
depolarization
80) Saltatory conduction is slow due to the presence of insulating myelin around an axon.
false
81) Axons with a smaller diameter can conduct nerve impulses more quickly than axons with a larger diameter.
false
86) The membrane potential moves from -70mV to -90 mV
hyperpolarization
89) Anion channels open causing the membrane potential to become more negative
hyperpolarization
92) An inhibitory postsynaptic potential (IPSP) promotes this change in membrane potential
hyperpolarization
94) Glycine and GABA open chloride ion channels and cause this change in membrane potential
hyperpolarization
87) The membrane potential moves from -60 mV to - 70 mV
repolarization
91) Potassium leak channels and the Na+/K+ pump restore resting membrane potential after action potential
repolarization
78) During depolarization, the membrane potential becomes more positive.
true
79) During the absolute refractory period, production of an action potential is not possible.
true
82) Electrical synapses are faster than chemical synapses due to the presence of gap junctions between cells.
true
83) Calcium ion entry into the axon terminal is necessary for the release of neurotransmitter into the synaptic cleft.
true
84) Neurotransmitters can be either excitatory or inhibitory depending upon the receptor present on the postsynaptic neuron.
true
85) Converting neural circuits are opposite to diverging neural circuits
true
106) Discuss the two main factors to influence conduction speed of an action potential.
Conduction speed is influenced by two main factors: 1) diameter of the axon, and 2) presence or absence of a myelin sheath. Larger axons have lower resistance to the conduction of an action potential, and current flows through them more easily. Saltatory conduction occurs in the presence of a myelin sheath while continuous conduction occurs in the absence of a myelin sheath. Since myelin is an excellent insulator of electrical charge, the flow of current is far more efficient in a myelinated axon. Therefore, saltatory conduction is significantly faster than continuous conduction.
105) Why is a neuron unable to produce an additional action potential during the absolute refractory period?
During the absolute refractory period, sodium ion channels may not be activated until they return to their resting states with their activation gates closed and their inactivation gates open. It is during this period that an additional action potential cannot be produced, no matter how strong the stimulus.
112) Receptors on a postsynaptic CNS neuron bind glutamate. Describe how the postsynaptic neuron responds.
Glutamate is the most common excitatory neurotransmitter in the CNS. Upon binding glutamate, the postsynaptic neuron opens channels that can pass both sodium and calcium ions. The postsynaptic neuron will experience an EPSP.
102) Explain how leak channels and gated channels differ.
Leak channels are always open while gated channels are closed at rest. Gated channels only open in response to certain stimuli. Leak channels allow ions to follow their gradient into or out of the cell. Gated channels may be ligand-gated, voltage-gated, or mechanically gated. Ligand-gated channels open in response to a chemical binding to the channel while voltage-gated channels open or close in response to changes in voltage across the membrane. Mechanically gated channels open in response to mechanical stimulation such as stretch, pressure, or vibrations.
108) What type of postsynaptic potential would be more likely to promote an action potential - an IPSP or EPSP? Explain
A small, local depolarization called an EPSP moves the membrane potential closer to threshold. If threshold is reached, an action potential is triggered. A small, local hyperpolarization known as an IPSP moves the membrane potential farther from threshold. Threshold is critical for achievement of an action potential. Thus, an EPSP is more likely to promote an action potential while an IPSP is less likely to promote an action potential.
107) Discuss the role of calcium ions in the transmission of an action potential at the synapse.
An action potential reaching the axon terminal triggers voltage-gated calcium ion channels to open. The presence of calcium ions in the axon terminal causes synaptic vesicles to release neurotransmitters into the synaptic cleft. Neurotransmitters bind to receptors on the postsynaptic neuron. Ion channels respond and a local potential is created.
111) Kelly takes an antihistamine for allergies. Explain why sleepiness is a side effect of this medicine.
Antihistamines are drugs that block histamine receptors outside the nervous system to alleviate allergy symptoms. However, most drugs also block histamine receptors within the CNS as well. Since histamine plays a role in arousal, blocking its action often leads to the side effect of drowsiness.
110) Acetylcholine (ACh) may excite postsynaptic neurons in the CNS; however, it may inhibit some postsynaptic neurons in the PNS. Explain how acetylcholine can be both excitatory and inhibitory.
Acetylcholine can have an excitatory effect if it induces an EPSP when it binds a receptor. An inhibitory effect results if it produces an IPSP in the postsynaptic neuron. The type of receptor to which the neurotransmitter ACh binds determines the postsynaptic response
39) Voltage-gated sodium channels have both an activation gate and: A) an inactivation gate. B) a leak gate. C) a threshold gate. D) a swinging gate.
a
26) Resting membrane potential is maintained by the Na+/K+ pump which brings: A) two potassium ions into the cytosol and three sodium ions into the extracellular fluid. B) three potassium ions into the cytosol and three sodium ions into the extracellular fluid. C) two potassium ions into the cytosol and two sodium ions into the extracellular fluid. D) three potassium ions into the cytosol and two sodium ions into the extracellular fluid.
a
28) What type of ion channels is always open? A) leak B) local C) active D) regulated
a
33) Using the information provided in this graph, which statement best summarizes the activity in this neuron? A) The cell gains positive charges, making the inside less negative. B) Positive charges are lost from the cell, making the inside more negative. C) The cells gains negative charges, making the inside more negative. D) The cell gains chloride ions, making the cell hyperpolarize.
a
34) What is more likely to promote an action potential? A) depolarization B) hyperpolarization C) repolarization D) absolute refractory period
a
