Ch 11C
At which point of the illustrated action potential would voltage-gated Na+ channels be mostly open but voltage-gated K+ channels be mostly closed?
B Voltage-gated Na+ channels open when the membrane potential reaches threshold. Voltage-gated K+ channels would be mostly open near C.
The interior of the cell becomes less negative due to an influx of sodium ions.
Depolarization
The all-or-none phenomenon as applied to nerve conduction states that the whole nerve cell must be stimulated for conduction to take place.
False
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.
What change in a neuron is being measured in the graph?
the voltage measured across the axon membrane at a specific point as an action potential travels past
An action potential is regarded as an example of a positive feedback. Which of the following examples below best illustrates the positive feedback aspect of an action potential?
A threshold stimulus will cause the opening of voltage gated sodium ion channels that will cause further depolarizing stimulus. This stimulus will open still more voltage gated sodium ion channels.
The neuron cannot respond to a second stimulus, no matter how strong
Absolute refractory period
Also called a nerve impulse transmitted by axons.
Action potential
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent area.
What type of conduction takes place in unmyelinated axons?
Continuous conduction
Where do most action potentials originate?
Initial segment
During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?
K+ channels close. Na+ channels go from an inactivated state to a closed state.
During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.
K+ ions diffusing through voltage-gated channels
The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.
K+ ions leaving the cell through voltage-gated channels
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
What is happening to voltage-gated channels at this point in the action potential?
Na+ channels are inactivating, and K+ channels are opening.
Which of the following correctly states the direction followed by the specified ions when their voltage-gated channels open?
Na+ ions move into the axon; K+ ions move out.
During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?
Na+ is entering the cell.
What characterizes repolarization, the second phase of the action potential?
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV
An exceptionally strong stimulus can trigger a response.
Relative refractory period
The specific period during which potassium ions diffuse out of the neuron due to a change in membrane permeability.
Repolarization
Tetraethylammonium (TEA) blocks voltage-gated K+ channels such that K+ cannot pass even when the channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron with TEA?
The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time.
Why does the action potential only move away from the cell body?
The areas that have had the action potential are refractory to a new action potential.
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.
Which of the following is NOT a difference between graded potentials and action potentials?
The magnitude of action potentials decrease as the impulse travels further away from the start of the impulse while graded potentials do not decrease in magnitude.
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
What event triggers the generation of an action potential?
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
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.
You discover that a new chemical compound interacts with K+ voltage-dependent channels. What would be the effect on a neuron if the chemical came into contact with the axonal membrane?
The neuron would be unable to repolarize.
Which of the following is not true of graded potentials?
They increase amplitude as they move away from the stimulus point.
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
The velocity of the action potential is fastest in which of the following axons?
a small myelinated axon
What type of stimulus is required for an action potential to be generated?
a threshold level depolarization
The period after an initial stimulus when a neuron is not sensitive to another stimulus is the ________.
absolute refractory period
During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?
at the end of the depolarization phase, as the membrane potential approaches its peak value
Which of the following is a factor that determines the rate of impulse propagation, or conduction velocity, along an axon?
degree of myelination of the axon
If a neuron had a mutation that prevented the production of voltage-gated Na+ channels, what function would the neuron NOT be able to accomplish?
depolarization leading to action potentials
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
Which membrane potential occurs because of the influx of Na+ through chemically gated channels in the receptive region of a neuron?
excitatory postsynaptic potential
Strong stimuli cause the amplitude of action potentials generated to increase.
false
What does the central nervous system use to determine the strength of a stimulus?
frequency of action potentials
Which of the following correctly describes a graded potential?
it can have amplitudes of various sizes
Saltatory conduction is made possible by ________.
the myelin sheath
A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.
true
During depolarization, the inside of the neuron's membrane becomes less negative.
true
In myelinated axons the voltage-regulated sodium channels are concentrated at the nodes of Ranvier.
true
The action potential is caused by permeability changes in the plasma membrane.
true
If the neuron membrane becomes more permeable to Na+, Na+ will transport across the membrane, causing the cell to depolarize.
true In either a graded or action potential, Na+ is transported into the cell faster than during resting potentials. As Na+ enters the cell, the inside of the cell becomes more positive, or depolarized.
Immediately after an action potential has peaked, which of the following channels will open?
voltage gated potassium channels
Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?
voltage-gated channel
