76 Questions
Which type of synapse is faster and coupled via gap junctions?
Electrical synapse
What is the size of the gap in electrical synapses?
3.5 nm
Which of the following is true about electrical synapses?
They weaken the signal as it is transmitted
What determines whether a neuron fires based on the 'add together' of all the tiny signals it receives from several other neurons?
Spatial summation
Which ion channel is most likely inhibited by this mechanism?
Ca2+
What is the equilibrium potential of K+?
-90 mV
What is the role of the electrical force in determining the equilibrium potential?
It is the force that exactly counter-balances the chemical force.
If the cell membrane was 1000X more permeable to K+ than to any other ion, what would be the membrane potential?
-90 mV
What would be the membrane potential if both K+ channels and Na+ channels were open and if the cell was exactly equally permeable to Na+ and K+?
-15 mV
What is the reversal potential of K+ (EK)?
-90 mV
Which of the following represents the main way that neurons code the intensity of their synaptic input?
Firing frequency represents the intensity of activity
What is the relationship between threshold voltage and firing frequency?
Increasing threshold voltage decreases firing frequency
What is the difference between inactivated and closed channels?
Inactivated channels are non-conducting, while closed channels are conducting
What happens to the membrane voltage when Na+ channels open?
The membrane becomes positive inside
What happens to the membrane voltage when K+ channels open?
The membrane becomes negative inside
Which of the following drugs raises the threshold and lowers excitability of neurons?
Lidocaine
According to the mnemonic for equilibrium potentials, which of the following statements is true?
The voltages for positive events are positive, while the voltages for negative events are negative.
Which equation represents the Nernst Equation for deriving equilibrium potentials?
$E = 2.3 \log \left( \frac{[ion]_o},{[ion]_i} \right)$
Which of the following is true about action potentials?
They are always the same - "All or none".
What is the basis of saltatory conduction?
Action potentials
Which of the following statements about electrotonic conduction is true?
It transmits electric field instantly.
What is the typical conduction velocity for alpha motor fibers?
100 m/s
Which of the following best describes temporal summation in neuronal signaling?
When the input neuron is firing fast enough so that the receiving neuron can 'add together' the many tiny signals
During an action potential, what happens when the voltage reaches the threshold?
Na+ conductance shoots up, Na+ current goes into the cell, and the membrane potential depolarizes
What causes the initial depolarization in an action potential?
Synaptic transmission where a neurotransmitter opens a ligand-gated channel
What happens during the positive feedback loop of depolarization in an action potential?
Na+ channels open and K+ channels open, leading to depolarization
What causes repolarization in an action potential?
Na+ channel inactivation and delayed rectifier K+ channels opening
What happens during the after-hyperpolarization phase of an action potential?
The voltage inside the cell temporarily goes slightly more negative than at rest
Which of the following best describes the resting membrane potential (RMP)?
The voltage across the cell membrane when it is at rest
What is the equilibrium potential of Na+ (ENa)?
+30 mV
Which ion channel is responsible for the initial depolarization in an action potential?
Na+ channels
What is the typical conduction velocity for C fibers?
10-20 meters per second
What is the difference between inactivated and closed channels?
Inactivated channels cannot open, while closed channels can open
What happens to the membrane voltage when K+ channels open?
The membrane voltage becomes more negative
What happens to the membrane voltage when Na+ channels open?
The membrane voltage becomes more positive
What happens during the after-hyperpolarization phase of an action potential?
The membrane potential becomes more negative
What happens during the positive feedback loop of depolarization in an action potential?
The membrane potential becomes more positive
During which phase of the action potential does the membrane voltage reach its peak?
Depolarization
What is the approximate duration of an action potential?
2-4 ms
What is the resting membrane potential (RMP) range?
-85 mV to -55 mV
What is the primary determinant of the resting membrane potential (RMP)?
Leak and inward rectifier currents
Which of the following accurately describes the effect of an increase in extracellular Na+ on the resting membrane potential (RMP)?
The RMP would become slightly less negative
What would happen to the resting membrane potential if extracellular K+ suddenly increased?
The RMP would become less negative
Why do graded potentials diminish over distance?
Voltage approaches zero as it travels along a resistor
Why do axons need action potentials to propagate signals long distances?
Action potentials restore and re-amplify signals
Which of the following is true about conduction velocity in neurons?
Alpha motor neurons have a higher conduction velocity than C fibers
Which of the following structural features increases conduction velocity in neurons?
Larger diameter
What is the effect of myelination on conduction velocity in neurons?
Increases conduction velocity
What is the purpose of Nodes of Ranvier in myelinated axons?
Increase conduction velocity
Which of the following is NOT a source of K+ permeability that causes K+ to flow out of the cell during the afterhyperpolarisation?
Outward rectifiers
Which of the following is true about a graded potential?
It can occur at synapses
What is the main transmembrane force on an ion at its equilibrium potential?
Chemical (diffusional) force
Which of the following drug classes does NOT block sodium channels as part of their mechanism of action?
Antidepressants
Which of the following is true about the velocity of blood in the aorta?
It is approximately 1 meter/second
Which of the following best describes the effect of selective serotonin reuptake inhibitors (SSRIs)?
They block the reuptake of serotonin from the synaptic cleft
What would happen if the membrane suddenly became 100X more permeable to Cl¯ ions than to any other ion?
The membrane potential would become clamped to ECl (e.g. -65 mV)
What is the definition of Na+ channel inactivation and how does it affect sodium channel activity during different phases of the action potential?
Na+ channel inactivation is the process whereby depolarization of the membrane leads to reduced (or eliminated) channel conductance. It reduces Na+ conduction during repolarization and after-hyperpolarization phases of the action potential.
Which of the following is true about the resting membrane potential (RMP) under the influence of this drug?
The RMP will move up toward ECl, possibly going as high as -65 mV.
What effect will the drug have on the repolarization of the action potential (AP)?
The repolarization of the AP will be delayed.
What effect will the drug have on the duration of the action potential (AP)?
The duration of the AP will be longer.
What effect will doubling the Na/K pump activity have on the resting membrane potential (RMP)?
The RMP will be hyperpolarized by 3 mV.
What effect will half-blocking the K+ current have on the resting membrane potential (RMP)?
The RMP will be depolarized, possibly by as much as half.
What effect will doubling the Na/K pump activity have on the electrogenic effects of the drug?
The electrogenic effects will be double.
According to the text, what would happen if the delayed rectifier K+ channels opened immediately upon depolarization?
The action potential would repolarize faster and smaller
According to the text, what are 5 ways to initiate a subthreshold stimulus in a neuron that might lead to an action potential?
EPSP from a synapse, an electrical signal from a nearby part of the same neuron, a signal via an electrical synapse, a receptor stimulus, a change in extracellular ion concentration
According to the text, why does Vm become more negative than the RMP during the after-hyperpolarization?
Increased K+ current due to the delayed rectifier, decreased Na+ current, equivalent amount of inward rectifier K+ current
According to the text, what would be the equilibrium potential of the nicotinic acetylcholine receptor if it is equally permeable to Na+ and K+?
-17.5 mV
Which of the following channels is responsible for the initial depolarization in an action potential?
Na+ channels
What is the main transmembrane force on an ion at its equilibrium potential?
Chemical force
Which of the following drugs raises the threshold and lowers excitability of neurons?
Carbamazepine
What is the effect of myelination on conduction velocity in neurons?
Increases conduction velocity
Which of the following best describes the effect of selective serotonin reuptake inhibitors (SSRIs)?
Inhibits serotonin reuptake
What is the typical conduction velocity for alpha motor fibers?
50-75 m/s
Which of the following is NOT a source of K+ permeability that causes K+ to flow out of the cell during the afterhyperpolarisation?
Na+ channels
What would be the membrane potential if both K+ channels and Na+ channels were open and if the cell was exactly equally permeable to Na+ and K+?
Resting membrane potential (RMP)
What happens during the positive feedback loop of depolarization in an action potential?
Membrane voltage increases exponentially
Test your knowledge on how neurons code the intensity of their synaptic input. Learn about the threshold voltage for action potential firing and how increasing excitation affects firing frequency.
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