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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 is happening to voltage-gated channels at this point in the action potential?
Na+ channels are inactivating, and K+ channels are opening.
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
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
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 the hyperpolarization phase of the action potential, voltage eventually returns to the resting membrane potential. What processes are primarily responsible for this return to the resting membrane potential?
Voltage-gated K+ channels close. K+ and Na+ diffuse through leakage channels.
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.
The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?
An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?
the generation of local currents
During action potential propagation 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 in the refractory period.
In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon?
The nodes are more permeable to ions
Where are action potentials regenerated as they propagate along a myelinated axon?
at the nodes of Ranvier
How do action potential propagation speeds compare in myelinated and unmyelinated axons?
Propagation is faster in myelinated axons.
The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.
The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?
The speed of action potential propagation would be slower.
Which of the following best describes the Na+ and K+ concentrations across a neuron's plasma membrane?
The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside.
What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?
maintaining the concentration gradients for Na+ and K+ across the cell membrane
Which of the following is the clearest example of a neuronal membrane's selective permeability?
K+ ions can diffuse across the membrane more easily than Na+ ions.
Suppose a drug is developed that blocks K+ leakage channels. The drug prevents ions from passing through those channels. If this drug was applied to a neuron, what would be the most immediate effect on that neuron?
The resting membrane potential would become less negative (more positive).
Imagine you changed the concentration of K+ outside a neuron such that the resting membrane potential changed to -80 mV (from the normal resting value of -70 mV). What have you changed?
the electrical gradient for K+ and the concentration gradient for K+
What is the electrochemical gradient of an ion?
the sum of the electrical and concentration gradients for that ion
Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?
The resting membrane potential would become less negative (more positive).
Which of the following is not one of the chemical classes into which neurotransmitters fall?
What does the difference in the K+ and Na+ concentration on either side of the plasma membrane (and permeability of the membrane to those ions) generate?
resting membrane potential
What type of stimulus is required for an action potential to be generated?
a threshold level stimulus
Multiple sclerosis (MS) is a disease in which the myelin sheaths are destroyed. What process does this interfere with, and what would be the consequence?
Demyelination interferes with saltatory conduction, which would result in a slowing down of nerve impulse propagation.
Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?
When a sensory neuron is excited by some form of energy, the resulting graded potential is called a(n) ________.
Which of the following is not true of graded potentials?
They increase amplitude as they move away from the stimulus point.
Neurons may be classified according to several characteristics. Which of the following is correct?
Group C fibers are not capable of saltatory conduction.
________ potentials are short-lived, local changes in membrane potential that can be either depolarized or hyperpolarized
In myelinated axons the voltage-regulated sodium channels are concentrated at the nodes of Ranvier.
When calcium ions enter the synaptic terminal,
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
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
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.
Which of the following circuit types is involved in the control of rhythmic activities such as the sleep-wake cycle, breathing, and certain motor activities (such as arm swinging when walking)?
Which membrane potential results in depolarization without a nerve impulse being generated?
excitatory postsynaptic potential
The synapse more common in embryonic nervous tissue than in adults is the ________.
When one or more presynaptic neurons fire in rapid order it produces a much greater depolarization of the postsynaptic membrane than would result from a single EPSP; this event is called ________ summation.
Which pattern or neural processing works in a predictable, all-or-nothing manner, where reflexes are rapid, automatic responses to stimuli in which a particular stimulus always causes the same response?
Which of the following is an excitatory neurotransmitter secreted by motor neurons innervating skeletal muscle?
3. integration center
4. motor neuron
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