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In a neuron, sodium and potassium concentrations are maintained by the sodium-potassium exchange pump such that __________. |
the sodium concentration is higher outside the cell than inside the cell and the potassium concentration is higher inside the cell than outside the cell. |
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The sodium-potassium exchange pump transports potassium and sodium ions in which direction(s)? |
Sodium ions are transported out of the cell. Potassium ions are transported into the cell. |
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Leak channels allow the movement of potassium and sodium ions by what type of membrane transport? |
channel-mediated diffusion |
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The electrochemical gradient for potassium ions when the transmembrane potential is at the resting potential (-70 mV) is caused by what? |
a chemical gradient going out of the cell and an electrical gradient going into the cell |
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What is the electrochemical gradient of an ion? |
the sum of the electrical and chemical gradients for that ion |
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In a typical neuron, what is the equilibrium potential for potassium? |
-90mV |
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The electrochemical gradient for sodium ions in a neuron when the transmembrane potential is at the resting potential is caused by what? |
chemical and electrical gradients both going into the cell |
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Compared to the electrical gradient for sodium at rest, the electrical gradient for potassium at rest is __________. |
in the same direction and of the same magnitude. |
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In a typical neuron, what is the equilibrium potential for sodium? |
+66mV |
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At rest, why is the transmembrane potential of a neuron (-70 mV) closer to the potassium equilibrium potential (-90 mV) than it is to the sodium equilibrium potential (+66 mV)? |
The membrane is much more permeable to potassium ions than to sodium ions. |
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Which of the following statements about receptor potentials is FALSE? |
The receptor potential is carried by neuroglia. |
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Which of the following is NOT a functional region of a neuron? |
medullary region |
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The conducting region of the neuron is the _______ |
axon |
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The typical concentration of sodium is |
lower than potassium intracellularly. |
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Which of the following describes a change from the resting membrane potential? |
a receptor potential, a synaptic potential or an action potentia |
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What effect did increasing the extracellular potassium have on the resting membrane potential? |
The resting membrane potential became less negative. |
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What effect did decreasing the extracellular sodium have on the resting membrane potential? |
Only a small change occurred, because the resting neuron is not very permeable to sodium. |
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The channels that provide for the movement of potassium in the resting neuron are _______. |
leakage |
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Establishing the resting membrane potential requires energy through the use of the _______. |
sodium-potassium pump |
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In what part of the neuron does the action potential typically initiate? |
initial segment of the axon |
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During an action potential of a neuron, what directly causes the different channels to open and close? |
the transmembrane potential (voltage) |
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What is the typical duration of a nerve action potential? |
2 ms |
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Around what transmembrane potential does threshold commonly occur? |
-60 mV |
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What ion is responsible for the depolarization of the neuron during an action potential? |
Na+ sodium |
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What type of membrane transport causes the depolarization phase of the action potential in neurons? |
diffusion |
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During an action potential, after the membrane potential reaches +30 mV, which event(s) primarily affect(s) the membrane potential? |
Voltage-gated sodium channels begin to inactivate (close) and voltage-gated potassium channels begin to open. |
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What ion causes repolarization of the neuron during an action potential? |
K+ (potassium) |
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What causes repolarization of the membrane potential during the action potential of a neuron? |
potassium efflux (leaving the cell) |
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What is primarily responsible for the brief hyperpolarization near the end of the action potential? |
voltage-gated potassium channels taking some time to close in response to the negative membrane potential |
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A nerve is _______. |
bundle of axons |
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The region on the neuron where action potentials are generated is called the ______. |
trigger zone |
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In this simulation, ___________________ will be used to stimulate the axon. |
voltage |
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We describe the regeneration of the action potential down the membrane of the axon of the neuron as _______. |
conduction or propagation |
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The minimum voltage that is required to generate an action potential is called the _______. |
threshold voltage |
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Increasing the voltage resulted in which of the following? |
no change to the action potential |
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An axon that is more negative than the resting membrane potential is said to be _______. |
hyperpolarized |
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If an increase in extracellular potassium depolarizes a neuron, which of the following would be correct? |
would change the membrane potential to a less negative value. |
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An action potential requires _______. |
voltage-gated sodium channels to open and sodium to flow with its electrochemical gradient |
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To reach threshold, the amount of sodium _______. |
entering the cell must overcome the potassium exiting |
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Which of the following blocks voltage-gated sodium channels? |
tetrodotoxin and lidocaine |
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Which of the following is used to block pain? |
lidocaine |
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hich of the following occurred in the presence of tetrodotoxin? |
The number of action potentials decreased. |
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Which of the following occurred in the presence of tetrodotoxin? |
An action potential was always seen at R1. |
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In the presence of lidocaine, the action potential was NOT affected at R1 because _______. |
lidocaine was applied downstream of R1 |
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The effects of lidocaine and tetrodotoxin were _______. |
similar, but tetrodotoxin had a greater effect |
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Action potential propagation begins (is first generated at) what region of a neuron? |
initial segment |
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Where are action potentials regenerated as they propagate along an unmyelinated axon? |
at every segment of the axon |
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The movement of what ion is responsible for the local currents that depolarize other regions of the axon to threshold? |
sodium (Na+) |
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In an unmyelinated axon, why doesn’t the action potential suddenly "double back" and start propagating in the opposite direction? |
The previous axonal segment is refractory. |
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Approximately how fast do action potentials propagate in unmyelinated axons in humans? |
1 meter per second |
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In contrast to the internodes of a myelinated axon, the nodes __________. |
have lower membrane resistance to ion movement |
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Where are action potentials regenerated as they propagate along a myelinated axon? |
at the nodes |
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The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________. |
saltatory propagation |
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ow do action potential propagation speeds in myelinated and unmyelinated axons compare? |
Propagation is faster in myelinated axons. |
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Multiple sclerosis (MS) is a disease that stops action potential propagation by destroying the myelin around (normally) myelinated axons. Which of the following best describes how MS stops action potential propagation? |
Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes. |
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Which of the following is described correctly? |
Schwann cells provide the myelination in the peripheral nervous system. |
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The rate with which an action potential travels along an axon _______. |
is called the conduction velocity and is measured in meters/sec |
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Which of the following describes a B fiber? |
medium diameter, lightly myelinated |
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The nodes of Ranvier are _______. |
locations on the axon where the myelin sheath is absent |
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Which fibers generate the smallest value for conduction velocity? |
C Fibers |
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The time interval for conduction would be shortest with |
the largest and most heavily myelinated axons |
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ncreasing the amount of myelination _______. |
decreases the time between action potentials |
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In this activity, the stimulus voltage used was _______. |
the same for all of the axons and suprathreshold for all of the axons |
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The small space between the sending neuron and the receiving neuron is the |
synaptic cleft |
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A molecule that carries information across a synaptic cleft is a |
neurotransmitter |
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When calcium ions enter the synaptic terminal, |
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron. |
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When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, |
ion channels in the plasma membrane of the receiving neuron open. |
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If a signal from a sending neuron makes the receiving neuron more negative inside, |
the receiving neuron is less likely to generate an action potential. |
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A synaptic cleft, or synaptic gap, can be found between a neuron and ______. |
All of them |
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The membrane potential that occurs when neurotransmitters bind to their receptors is called |
a postsynaptic potential |
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The release of neurotransmitter occurs _______. |
at the axon terminal |
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Which of the following occurs first? An action potential arrives at the axon terminal. |
An action potential arrives at the axon terminal. |
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At a chemical synapse, the intensity of the stimulus is coded by _______. |
the amount of neurotransmitter released and the amount of calcium that enters the axon terminal |
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When the calcium was removed from the extracellular solution, _______. |
no neurotransmitter was released |
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When magnesium was added to the extracellular solution, _______. |
the amount of neurotransmitter released decreased |
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Calcium and magnesium are both _______. |
divalent cations |
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What type of conduction takes place in unmyelinated axons? |
continuous conduction |
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An action potential is self-regenerating because __________. |
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment |
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Why does regeneration of the action potential occur in one direction, rather than in two directions? |
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential. |
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What is the function of the myelin sheath? |
The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals. |
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What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization? |
Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open. |
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In which type of axon will velocity of action potential conduction be the fastest? |
Myelinated axons with the largest diameter |
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A single action potential is described as _______. |
no graded |
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A suprathreshold stimulus results in _______. |
more action potentials |
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A depolarizing synaptic potential is also known as _______. |
an excitatory postsynaptic potential |
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The stimulus for graded potentials includes _______. |
sensory stimuli and neurotransmitter |
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A weak, subthreshold stimulus will result in _______. |
a small depolarization at the receiving end of the neuron |
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Which stimulus was at or above threshold? |
the moderate and strong stimuli |
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increasing the strength of the stimulus applied to the sensory receptor increased _______. |
the frequency of action potentials in the sensory neuron, the amount of neurotransmitter released at the axon terminal of the sensory neuron and the frequency of action potentials in the interneuron |
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An excitatory postsynaptic potential occurs _______. |
at the receiving end of the interneuron |
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