A & P Neurons

In a typical neuron, what is the equilibrium potential for sodium? +66 mV -70 mV -90 mV +30 mV

+66 mV The sodium equilibrium potential is the transmembrane potential at which the chemical and electrical gradients would be equal in magnitude, but opposite in direction. In a typical neuron, sodium tends to enter the cell because of the large concentration of sodium ions outside the cell relative to the concentration of sodium ions inside the cell (that is, the concentration gradient for sodium). Therefore, the equilibrium potential for sodium must be positive, because it must oppose the entry of sodium ions. The specific value of the sodium equilibrium potential depends on the size of the sodium chemical gradient.

Around what transmembrane potential does threshold commonly occur? -60 V -60 mV -70 mV +60 mV

-60 mV At approximately -60 mV, an action potential is initiated. A transmembrane potential -60 mV corresponds to a depolarization of 10-15 mV away from the resting membrane potential.

What is the value for the resting membrane potential for most neurons? -90 mV +30 mV -70 mV

-70 mV the resting membrane potential for neurons depends on the distribution of both Na+ and K+ across the cell membrane. The potential is closer to the equilibrium potential of K+ because the cell is more permeable to K+.

What would be the equilibrium potential of an undisturbed cell if the plasma membrane were freely permeable to potassium ions only? +66 mV -90 mV +30 mV -70 mV

-90 mV

In a typical neuron, what is the equilibrium potential for potassium? -70 mV 0 mV +66 mV -90 mV

-90 mV The potassium equilibrium potential is the transmembrane potential at which the chemical and electrical gradients would be equal in magnitude, but opposite in direction. In neurons, potassium tends to exit the cell because of the greater concentration of potassium ions inside the cell than outside the cell (that is, the concentration gradient for potassium). Therefore, the equilibrium potential for potassium must be negative, because it must oppose the exit of potassium ions. The specific value of the potassium equilibrium potential depends on the size of the potassium chemical gradient.

The equilibrium potential for potassium ion occurs at approximately -70 mV. 0 mV. -90 mV. +66 mV. -55 mV.

-90 mV.

Approximately how fast do action potentials propagate in unmyelinated axons in humans? 12 meters per second 120 meters per second 1 meter per second 0.1 meters per second

1 meter per second While 1 m per second (2 mph) seems slow, most axons are short, and these speeds are fast enough for low-priority information such as smell (olfaction), temperature, and general touch sensations. Unmyelinated type C fibers have propagation speeds in this range.

What is the magnitude (amplitude) of an action potential? 100 mV 70 mV 30 mV

100 mV the membrane goes from -70 mV to +30 mV. Thus, during the action potential, the inside of the cell becomes more positive than the outside of the cell.

What is the typical duration of a nerve action potential? 20 ms 0.2 ms 200 ms 2 ms

2 ms From initiation to completion, the action potential is rarely over a few milliseconds. This is an extremely brief period of time-about as long as it takes for a handgun bullet to travel one meter.

At the normal resting potential of a typical neuron, its Na-K ion exchange pump transports 3 intracellular sodium ions for 2 extracellular potassium ions. 3 extracellular sodium ions for 2 intracellular potassium ions. 3 intracellular sodium ions for 1 extracellular potassium ion. 2 intracellular sodium ions for 1 extracellular potassium ion. 1 intracellular sodium ion for 2 extracellular potassium ions.

3 intracellular sodium ions for 2 extracellular potassium ions.

The following are the main steps in the generation of an action potential. 1. Sodium channels are inactivated. 2. Voltage-gated potassium channels open and potassium moves out of the cell, initiating repolarization. 3. Sodium channels regain their normal properties. 4. A graded depolarization brings an area of an excitable membrane to threshold. 5. A temporary hyperpolarization occurs. 6. Sodium channel activation occurs. 7. Sodium ions enter the cell and depolarization occurs. The proper sequence of these events is 6, 7, 4, 1, 2, 3, 5. 4, 2, 5, 6, 7, 3, 1. 2, 4, 6, 7, 1, 3, 5. 4, 6, 7, 3, 2, 5, 1. 4, 6, 7, 1, 2, 3, 5.

4, 6, 7, 1, 2, 3, 5.

Choose the correct sequence of events that occur at a cholinergic synapse. 1 - ACh binds to sodium channel receptors. 2 - The synaptic knob reabsorbs choline from the synaptic cleft. 3 - ACh is released through the exocytosis of synaptic vesicles. 4 - An arriving action potential depolarizes the synaptic knob. 5 - ACh is broken down by AChE. 4-3-1-5-2 2-1-4-3-5 5-4-3-1-2 3-4-5-2-1

4-3-1-5-2

Which of the following best describes how ACh causes depolarization of the postsynaptic membrane? ACh causes vesicles to fuse, releasing neurotransmitter into the synaptic cleft. ACh activates acetylcholinesterase (AChE). ACh opens voltage-gated calcium channels. ACh opens ACh receptors.

ACh opens ACh receptors. ACh receptors on the postsynaptic membrane are chemically gated ion channels. These channels open when they bind ACh. Once open, these channels allow sodium to enter, depolarizing the cell. Chemically gated channels are often called "receptors" because they must "receive" (or bind) a particular chemical before they can open.

What is the primary role of acetylcholinesterase (AChE) at a cholinergic synapse? AChE depolarizes the postsynaptic cell. AChE binds to ACh receptors, causing them to open. AChE releases acetylcholine into the synaptic cleft. AChE degrades acetylcholine in the synaptic cleft.

AChE degrades acetylcholine in the synaptic cleft. AChE is an enzyme that breaks down or degrades ACh in the synaptic cleft. Degradation of ACh and removal of acetylcholine components, allows the postsynaptic cell to return to its resting potential after depolarization.

Which is the correct statement regarding action potentials? Action potentials depend on voltage-gated channels. Action potentials depend on leak channels. Action potentials are localized changes in the transmembrane potential. An action potential begins with the opening of voltage-gated potassium ion channels.

Action potentials depend on voltage-gated channels.

Which of the following would not have an effect on synaptic function? prevent neurotransmitter inactivation block neurotransmitter binding to receptors interfere with neurotransmitter synthesis interfere with neurotransmitter reuptake All of the above would affect synaptic function.

All of the above would affect synaptic function.

Which of the following accurately describes the all-or-none principle? When partial repolarization has occurred, the membrane can respond only to a larger-than-normal stimulus. All stimuli that bring the membrane to threshold generate identical action potentials. After depolarization, the membrane cannot respond to further stimulation. The electrical and chemical gradients across the membrane are equal and opposite.

All stimuli that bring the membrane to threshold generate identical action potentials.

Which of the following best describes the order of events in synaptic activity? Extracellular calcium enters the synaptic knob, triggering exocytosis of ACh. An action potential arrives and depolarizes the synaptic knob. ACh binds to receptors and depolarizes postsynaptic membrane. ACh is removed by AChE. An action potential arrives and depolarizes the synaptic knob. Extracellular calcium enters the synaptic knob, triggering exocytosis of ACh. ACh binds to receptors and depolarizes postsynaptic membrane. ACh is removed by AChE. An action potential arrives and depolarizes the synaptic knob. Extracellular calcium enters the synaptic knob, triggering exocytosis of ACh. ACh is removed by AChE. ACh binds to receptors and depolarizes postsynaptic membrane. ACh is removed by AChE. ACh binds to receptors and depolarizes postsynaptic membrane. An action potential arrives and depolarizes the synaptic knob. Extracellular calcium enters the synaptic knob, triggering exocytosis of ACh.

An action potential arrives and depolarizes the synaptic knob. Extracellular calcium enters the synaptic knob, triggering exocytosis of ACh. ACh binds to receptors and depolarizes postsynaptic membrane. ACh is removed by AChE. The correct sequence starts with a neural signal at the presynaptic cell, followed by the release of neurotransmitter, the depolarization of postsynaptic cell, and finally, degradation of acetylcholine. Neurotransmitters, like ACh, transfer information between a neuron and a postsynaptic cell. This process gets a "message" across a physical separation much like sending a text to your friend who is across town.

How is an action potential propagated along an axon? Stimuli from the graded (local) potentials from the soma and dendrites depolarize the entire axon. An efflux of potassium from the current action potential depolarizes the adjacent area. An influx of sodium ions from the current action potential depolarizes the adjacent area.

An influx of sodium ions from the current action potential depolarizes the adjacent area. Yes, the influx of sodium ions depolarizes adjacent areas, causing the membrane to reach threshold and cause an action potential. Thus, the action potential is regenerated at each new area.

Which of the following best describes the role of calcium in synaptic activity? Calcium enters the presynaptic cell and causes the release of ACh. Calcium diffuses across the synaptic cleft to bind with receptors on the postsynaptic cell. Calcium enters the postsynaptic cell and causes depolarization. Calcium breaks down acetylcholine.

Calcium enters the presynaptic cell and causes the release of ACh. As a presynaptic action potential reaches the synaptic terminal, voltage-gated calcium channels open. The open calcium channels allow calcium to diffuse into the synaptic terminal. This calcium influx causes synaptic vesicles to fuse with the presynaptic membrane. The content of these vesicles - acetylcholine - is then released into the synaptic cleft. Although this process consists of many steps, it happens quickly. It only takes 0.2-0.5 msec from when an action potential arrives at the synaptic terminal to when depolarization starts to occur in the postsynaptic cell.

________ open or close in response to binding specific molecules. Voltage-gated channels Leak channels Chemically gated channels Activated channels Mechanically-gated channels.

Chemically gated channels

What type of conduction takes place in unmyelinated axons? Continuous conduction Electrical conduction Synaptic transmission Saltatory conduction

Continuous conduction Yes! An action potential is conducted continuously along an unmyelinated axon from its initial segment to the axon terminals. The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+ channels open in every consecutive segment of the axon, not at nodes of Ranvier.

When is a neuron in the relative refractory period

During hyper polarisation

Which of the following interactions between electrical and chemical gradients does not lead to the establishment of a neuron's resting potential? Potassium ions are attracted to the negative charges inside the cell. Chemical forces tend to drive potassium ions out of the cell. Chemical and electrical forces both favor sodium ions entering the cell. Potassium ions are repulsed by positive charges outside the cell. Electrical forces push sodium ions out of the cell.

Electrical forces push sodium ions out of the cell.

When membrane potential approaches the potassium equilibrium potential, what is happening

Hyperpolarisation

Which of the following is defined as a graded hyperpolarization of the postsynaptic membrane? equilibrium potential IPSP resting potential EPSP

IPSP

In a graph what happens when there's a sudden inflxux of sodium ions?

IT depolarises. There is a steep positive gradient towards +30mV

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. Activation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open. Inactivation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open. Activation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.

Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open. Yes! Closing of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+ channels open.

Choose the correct pairing of events that occur in the formation of an action potential to the corresponding changes in the transmembrane potential. Resting potential; +30 mV Potassium channels close; -60 mV Inactivation of sodium channels; +30 mV Depolarization to threshold; +10 mV

Inactivation of sodium channels; +30 mV

Where do most action potentials originate? Cell body Axon terminal Nodes of Ranvier Initial segment

Initial segment The first part of the axon is known as the initial segment. The initial segment is adjacent to the tapered end of the cell body, known as the axon hillock.

How would the absolute refractory period be affected if voltage-regulated sodium channels failed to inactivate? It would be basically unaffected. It would last indefinitely. It would be much briefer

It would last indefinitely.

What ion causes repolarization of the neuron during an action potential? K+ (potassium) Ca2+ (calcium) Na+ (sodium) Mg2+ (magnesium)

K+ (potassium) The exit of potassium from the cell causes the cell to become more negative, repolarizing the membrane. The exit of potassium ions through open channels is caused by the large concentration of potassium ions inside the neuron compared to the concentration of potassium ions outside the neuron (the chemical gradient for potassium). Even though the transmembrane potential during most of the repolarization phase is negative, this small electrical gradient (tending to pull potassium ions inward) is not enough to change the overall outward direction of the potassium electrochemical gradient.

The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____. Na+; Cl- K+; Cl- Na+; K+ K+; Na+

K+; Na+ more K+ moves out of the cell than Na+ moves into the cell, helping to establish a negative resting membrane potential

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel? Ligand-gated channels Voltage-gated channels Sodium-potassium ATPases Leak channels

Leak channels Leak channels for Na+ and K+ are ubiquitous, and they allow for the diffusion of these ions across plasma membranes.

________ channels open or close in response to physical distortion of the membrane surface. Voltage-gated Leak Mechanically gated Chemically gated Active

Mechanically gated

In which type of axon will velocity of action potential conduction be the fastest? Unmyelinated axons of the shortest length Myelinated axons with the smallest diameters Myelinated axons with the largest diameter Unmyelinated axons with the largest diameter

Myelinated axons with the largest diameter Yes! The large diameter facilitates the flow of depolarizing current through the cytoplasm. The myelin sheath insulates the axons and prevents current from leaking across the plasma membrane.

What ion is responsible for the depolarization of the neuron during an action potential? Ca2+ (calcium) K+ (potassium) Cl- (chloride) Na+ (sodium)

Na+ (sodium) The influx of sodium ions causes the rapid depolarization during the action potential. The influx of sodium ions through open channels is favored by two factors. (1) The sodium concentration inside the neuron is only about 10% of the sodium concentration outside the neuron. (2) Most of the time, the interior of the cell is electrically negative, which is attractive for the positively charged sodium ions.

The concentrations of which two ions are highest outside the cell. Na+ and A- (negatively charged proteins) Na+ and Cl- K+ and Cl- K+ and A- (negatively charged proteins)

Na+ and Cl- both Na+ and Cl- are in higher concentrations outside the cell.

In an undisturbed cell, which of the following can diffuse through leak channels? Pr- Na+ and Pr- Na+ and K+ K+ and Pr-

Na+ and K+

The Na+-K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped? K+ is pumped out of the cell and Na+ is pumped into the cell. Na+ is pumped out of the cell and K+ is pumped into the cell. Both Na+ and K+ are pumped out of the cell. Both Na+ and K+ are pumped into the cell.

Na+ is pumped out of the cell and K+ is pumped into the cell. Na+ is pumped out of the cell against its electrochemical gradient and K+ is pumped into the cell against its concentration gradient.

What prevents the Na+ and K+ gradients from dissipating? Na+ and K+ leaks H+-K+ ATPase Na+ cotransporter Na+-K+ ATPase

Na+-K+ ATPase Also known as the Na+-K+ pump, or simply the pump, this transporter moves three Na+ out of the cell and two K+ into the cell for every ATP it hydrolyzes. This pumping action prevents the Na+ and K+ gradients from running down as these ions passively move through leak channels.

What characterizes repolarization, the second phase of the action potential? As the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mV. Before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mV. Once the membrane depolarizes to a threshold value of approximately -55 mV, it repolarizes to its resting value of -70 mV. Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. Yes! The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value.

How do action potential propagation speeds in myelinated and unmyelinated axons compare? Propagation speeds are similar in both axon types. Propagation is faster in unmyelinated axons. Propagation is faster in myelinated axons. Propagation in myelinated axons is faster over short distances, but slower over long distances.

Propagation is faster in myelinated axons. The internode segments of myelinated axons allow local currents to travel quickly between nodes where the action potential is regenerated. This leaping of action potentials from node to node is several times faster than the continuous propagation found in unmyelinated axons. Myelinated axons also tend to have larger diameters, which enhances propagation speed.

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference? Resting membrane potential (RMP) Threshold potential Action potential Positive membrane potential

RMP The resting membrane potential is the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.

The sodium-potassium exchange pump transports potassium and sodium ions in which direction(s)? Sodium and potassium ions are both transported out of the cell. Sodium ions are transported out of the cell. Potassium ions are transported into the cell. Sodium ions are transported into the cell. Potassium ions are transported out of the cell. Sodium and potassium ions are both transported into the cell.

Sodium ions are transported out of the cell. Potassium ions are transported into the cell. The energy of ATP is used to actively transport potassium and sodium ions against their electrochemical gradients. Potassium and sodium ions diffuse in the opposite direction through channels.

Which of the following definitions or descriptions is correct? An inhibitory postsynaptic potential is a graded depolarization of the postsynaptic membrane. An excitatory postsynaptic potential is a graded hyperpolarization of the postsynaptic membrane. Spatial summation involves multiple synapses that are active simultaneously. Temporal summation occurs when a single synapse depolarizes once.

Spatial summation involves multiple synapses that are active simultaneously.

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. The flow of the sodium ions only goes in one direction—away from the cell body

The areas that have had the action potential are refractory to a new action potential. Yes, sodium channels are inactivated in the area that just had the action potential.

Puffer fish poison blocks voltage-gated sodium channels like a cork. What effect would this neurotoxin have on the function of neurons? Action potentials would lack a repolarization phase. Neurons would depolarize more rapidly. The axon would be unable to generate action potentials. The absolute refractory period would be shorter than normal. None, because the chemically gated sodium channels would still function.

The axon would be unable to generate action potentials.

Why does regeneration of the action potential occur in one direction, rather than in two directions? The activation gates of voltage-gated K+ channels open in the node, or segment, that has just depolarized. The activation gates of voltage-gated Na+ channels close in the node, or segment, that has just depolarized. The inactivation gates of voltage-gated K+ channels close in the node, or segment, that has just fired an action potential. The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.

The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential. Yes! At the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+ channels become absolutely refractory to another depolarizing stimulus.

If the potassium permeability of a resting neuron increases above the resting permeability, what effect will this have on the transmembrane potential? There will be almost no effect on transmembrane potential. The inside of the membrane will become more positive. The membrane will become depolarized. The inside of the membrane will become more negative. The inside of the membrane will become more negative and the membrane will become depolarized.

The inside of the membrane will become more negative.

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you? There is no electrical potential difference between the inside and the outside surfaces of the plasma membrane. The inside surface of the plasma membrane is much more negatively charged than the outside surface. The inside surface of the plasma membrane is much more positively charged than the inside surface. The outside surface of the plasma membrane is much more negatively charged than the inside surface.

The inside surface of the plasma membrane is much more negatively charged than the outside surface. The inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+.

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 concentration of potassium ions inside the cell is greater than the concentration of sodium ions outside the cell. The membrane is much more permeable to potassium ions than to sodium ions. For each ATP hydrolyzed, the sodium-potassium exchange pump transports more sodium ions out of the cell (three) than it transports potassium ions into the cell (two). There are more negatively charged proteins inside the cell than outside the cell.

The membrane is much more permeable to potassium ions than to sodium ions. The greater number of potassium leak channels allows potassium ions to more easily cross the membrane than do sodium ions.

What characterizes depolarization, the first phase of the action potential? The membrane potential changes from a negative value to a positive value. The membrane potential changes to a much more negative value. The membrane potential changes to a less negative (but not a positive) value. The membrane potential reaches a threshold value and returns to the resting state.

The membrane potential changes from a negative value to a positive value. The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value.

What event triggers the generation of an action potential? The membrane potential must return to its resting value of -70 mV from the hyperpolarized value of -80 mV. The membrane potential must depolarize from the resting voltage of -70 mV to its peak value of +30 mV. The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV. The membrane potential must hyperpolarize from the resting voltage of -70 mV to the more negative value of -80 mV.

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV. Yes! This is the minimum value required to open enough voltage-gated Na+ channels so that depolarization is irreversible.

What is the function of the myelin sheath? The myelin sheath decreases the resistance of the axonal membrane to the flow of charge. The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals. The myelin sheath decreases the speed of action potential conduction from the initial segment to the axon terminals. The myelin sheath increases the insulation along the entire length of the axon.

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals. Yes! The myelin sheath increases the velocity of conduction by two mechanisms. First, myelin insulates the axon, reducing the loss of depolarizing current across the plasma membrane. Second, the myelin insulation allows the voltage across the membrane to change much faster. Because of these two mechanisms, regeneration only needs to happen at the widely spaced nodes of Ranvier, so the action potential appears to jump.

Which of the following would occur in a resting membrane? The opening of sodium channels will cause depolarization. The opening of sodium channels will cause hyperpolarization. The closing of potassium channels will cause hyperpolarization. The opening of potassium channels will cause depolarization.

The opening of sodium channels will cause depolarization.

Curare is a drug that prevents ACh from binding to ACh receptors. How would you expect curare to affect events at a cholinergic synapse? The postsynaptic cell would not depolarize. Calcium would not diffuse into the presynaptic neuron. Vesicles would not release ACh. Acetylcholinesterase (AChE) would not break down ACh.

The postsynaptic cell would not depolarize. Depolarization of the postsynaptic membrane is due to sodium ions entering the cell through open ACh receptors. These receptors only open when ACh is bound. Because curare prevents this binding, curare would also prevent the depolarization of the postsynaptic cell. Curare has similar effects at the neuromuscular junction, where curare blocks synaptic activity and prevents muscle contraction.

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. The extracellular sodium concentration is too low around the previous axonal segment for an action potential to be (re)generated. Positive charges only move in one direction. New action potential generation near the soma repels previously generated action potentials.

The previous axonal segment is refractory. A propagating action potential always leaves a trail of refractory membrane in its wake. The trailing membrane takes some time to recover from the action potential it just experienced, largely because the membrane's voltage-gated sodium channels are inactivated. By the time this membrane segment is ready to (re)generate another action potential, the first propagating action potential is long gone.

The plasma membrane is much more permeable to K+ than to Na+. Why? The Na+-K+ pumps transport more K+ into cells than Na+ out of cells. There are many more voltage-gated K+ channels than voltage-gated Na+ channels. There are many more K+ leak channels than Na+ leak channels in the plasma membrane. Ligand-gated cation channels favor a greater influx of Na+ than K+.

There are many more K+ leak channels than Na+ leak channels in the plasma membrane. The concentration gradient and the large number of K+ leak channels allow for rather robust K+ diffusion out of a cell. In contrast, the concentration gradient and the relatively few Na+ leak channels allow for much less Na+ diffusion into a cell.

Dendrites contain numerous chemically gated ion channels. True or false

True, they relate to synaptic transmission

What opens first in response to a threshold stimulus? Voltage-gated Na+ channels Ligand-gated cation channels Ligand-gated Cl- channels Voltage-gated K+ channels

Voltage-gated Na+ channels The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm

What is the first change to occur in response to a threshold stimulus? Voltage-gated Ca2+ channels change shape, and their activation gates open. Voltage-gated Na+ channels change shape, and their activation gates open. Voltage-gated K+ channels change shape, and their activation gates open. Voltage-gated Na+ channels change shape, and their inactivation gates close.

Voltage-gated Na+ channels change shape, and their activation gates open Yes! The activation gates of voltage-gated Na+ channels open very rapidly in response to threshold stimuli. The activation gates of voltage-gated K+ channels are comparatively slow to open.

During an action potential, after the membrane potential reaches +30 mV, which event(s) primarily affect(s) the membrane potential? Voltage-gated potassium channels begin to open and the sodium-potassium exchange pump begins removing the excess Na+ ions from the inside of the cell. Voltage-gated sodium channels begin to inactivate (close) and voltage-gated potassium channels begin to open. Voltage-gated sodium channels begin to inactivate (close). Voltage-gated sodium channels begin to inactivate (close) and the sodium-potassium exchange pump begins removing the excess sodium ions from the inside of the cell.

Voltage-gated sodium channels begin to inactivate (close) and voltage-gated potassium channels begin to open. The repolarization phase of the action potential involves decreasing sodium influx via inactivation of sodium channels and increasing potassium efflux (exit) via opening potassium channels. Both of these processes begin near the peak of the action potential.

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 node membrane more easily becomes refractory. Without myelin, the internode membrane resistance increases, preventing local currents from reaching adjacent nodes. Without myelin, the internode membrane is depolarized more easily. Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes.

Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes. Myelin increases the membrane resistance of the axon section it surrounds, allowing local currents to travel between nodes, even though they are 1-2 mm apart. Removing myelin decreases the membrane resistance of internode regions. This shortens the distance that local currents travel because more charge now exits at the internode regions before it reaches the next node.

The electrochemical gradient for potassium ions when the transmembrane potential is at the resting potential (-70 mV) is caused by what? chemical and electrical gradients both going out of the cell chemical and electrical gradients both going into the cell a chemical gradient going out of the cell and an electrical gradient going into the cell a chemical gradient going into the cell and an electrical gradient going out of the cell

a chemical gradient going out of the cell and an electrical gradient going into the cell The higher concentration of potassium inside the cell than outside the cell results in an outward chemical gradient. However, the electrical gradient is in the opposite direction (inward) because, at the resting potential, the inside of the cell is more negative, which is attractive to the positively charged potassium ions.

The acetylcholine receptor is an example of what type of channel? a leak channel a voltage-gated channel a chemically gated channel a mechanically gated channel

a chemically gated channel Chemically gated channels open when they bind a specific molecule. This binding causes the channel to open, which allows ions to pass. The acetylcholine receptor is an example of this channel type because it opens when acetylcholine binds. As its name implies, the acetylcholine receptor "receives" acetylcholine before opening.

The velocity of the action potential is fastest in which of the following axons? a large unmyelinated axon a small myelinated axon a small unmyelinated axon

a small myelinated axon Yes, the myelination acts as insulation and the action potential is generated only at the nodes of Ranvier. Propagation along myelinated axons is known as saltatory conduction.

The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned? acetylcholine glutamate

acetylcholine Yes, acetylcholine is broken down by acetylcholinesterase before being returned to the presynaptic neuron's axon terminal.

In the process of continuous action potential propagation, the action potential is triggered by graded depolarization of the initial segment. at threshold, sodium channels begin to open rapidly. local currents depolarize the region just adjacent to the active zone. all of the above none of the above

all of the above

Ions can move across the plasma membrane in which of the following ways? through voltage-gated channels as in the action potential through passive or leak channels by ATP-dependent ion pumps like the sodium-potassium exchange pump through chemically-gated channels as in neuromuscular transmission all of the above

all of the above

The effect that a neurotransmitter has on the postsynaptic membrane depends on the frequency of neurotransmitter release. the nature of the neurotransmitter. the characteristics of the receptors. the quantity of neurotransmitters released. all of the above

all of the above

The all-or-none principle states that only sensory stimuli can activate action potentials. all stimuli will produce identical action potentials. the greater the magnitude of the stimuli, the greater the magnitude of the action potential. all stimuli great enough to bring the membrane to threshold will produce identical action potentials. only motor stimuli can activate action potentials.

all stimuli great enough to bring the membrane to threshold will produce identical action potentials.

IPSPs (inhibitory postsynaptic potentials) block the efflux of potassium ions. are graded hyperpolarizations. increase membrane permeability to sodium ions. are graded depolarizations. block the efflux of calcium ions.

are graded hyperpolarizations.

Oligodendrocytes: maintain the blood-brain barrier. assist in producing, circulating, and monitoring the CSF. are the myelin-producing glial cells in the PNS. are the myelin-producing glial cells in the CNS.

are the myelin-producing glial cells in the CNS.

Where are action potentials regenerated as they propagate along an unmyelinated axon? at the internodes at myelin at every segment of the axon at the nodes

at every segment of the axon In unmyelinated axons, the action potential is regenerated continuously along every segment of the axon (continuous propagation). In humans, only small diameter axons (for example, type C fibers) are unmyelinated. These neurons carry low-priority information, such as smell (olfaction) and temperature sensations.

Where are action potentials regenerated as they propagate along a myelinated axon? at every segment of the axon at the internodes at myelin at the nodes

at the nodes In myelinated axons, voltage-gated sodium channels are largely restricted to the nodes between myelinated internodes. Therefore, action potentials only regenerate at the nodes. The high membrane resistance of the internodes ensures that local currents generated at one node will quickly bring the next node to threshold, even though it is 1-2 mm away.

Where in the neuron is an action potential initially generated? axon hillock soma and dendrites anywhere on the axon

axon hillock this region (first part of the axon) receives local signals (graded potentials) from the soma and dendrites and has a high concentration of voltage-gated Na+ channels.

The axon is connected to the cell body at the collaterals. synapse. synaptic knobs. telodendria. axon hillock.

axon hillock.

The site in the neuron where EPSPs and IPSPs are integrated is the chemical synapse. synaptic knob. axon hillock. dendritic membrane. electrical synapse.

axon hillock.

Opening of sodium channels in the axon membrane causes both depolarization and increased positive charge inside the membrane. repolarization. increased positive charge inside the membrane. depolarization. hyperpolarization.

both depolarization and increased positive charge inside the membrane.

During depolarization, which gradient(s) move(s) Na+ into the cell? only the chemical gradient only the electrical gradient Na+ does not move into the cell. Na+ moves out of the cell. both the electrical and chemical gradients

both the electrical and chemical gradients a positive ion is driven into the cell because the inside of the cell is negative compared to the outside of the cell, and Na+ is driven into the cell because the concentration of Na+ is greater outside the cell.

The ion that triggers the release of acetylcholine into the synaptic cleft is magnesium. sodium. calcium. potassium. chloride.

calcium.

The ________ nervous system is composed of the brain and spinal cord. peripheral efferent central afferent autonomic

central

Leak channels allow the movement of potassium and sodium ions by what type of membrane transport? active transport channel-mediated diffusion facilitated diffusion simple diffusion

channel-mediated diffusion Ions move through leak channels because of chemical and electrical gradients.

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 a chemical gradient going out of the cell and an electrical gradient going into the cell a chemical gradient going into the cell and an electrical gradient going out of the cell chemical and electrical gradients both going out of the cell

chemical and electrical gradients both going into the cell The higher concentration of sodium outside the cell than inside the cell, creates an inward chemical gradient. In addition, the electrical gradient for sodium is also inward becuase, at the resting potential, the inside of the cell is relatively more negative than the outside, which is attractive to the positively charged sodium ions.

Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane. voltage-gated; postsynaptic voltage-gated; presynaptic chemically gated; postsynaptic chemically gated; presynaptic

chemically gated; postsynaptic Yes, the neurotransmitter is a chemical released from the presynaptic membrane, so it would open chemically gated channels on the postsynaptic membrane.

Branches that may occur along an axon are called synaptic knobs. dendrites. synapses. hillocks. collaterals.

collaterals

A shift of the resting transmembrane potential toward 0 mV is called ________

depolarisation

What causes calcium channels in the synaptic knob to open? depolarization of the presynaptic membrane due to an arriving action potential the binding of calcium the binding of ACh depolarization of the presynaptic membrane due to graded potentials

depolarization of the presynaptic membrane due to an arriving action potential When an action potential reaches the synaptic knob, voltage-gated calcium channels open. This allows Ca2+ to enter the neuron, causing ACh-containing vesicles to fuse with the plasma membrane. At rest, the concentration of calcium is very low inside the synaptic knob. This means that the small amount of calcium entering through channels can quickly change the calcium concentration several-fold.

Raising the potassium ion concentration in the extracellular fluid surrounding a nerve cell will have which effect? hyperpolarize it increase the magnitude of the potassium equilibrium potential depolarize it decrease the magnitude of the sodium equilibrium potential increase the magnitude of the sodium equilibrium potential

depolarize it

An action potential is self-regenerating because __________. repolarizing currents established by the efflux of Na+ flow down the axon and trigger an action potential at the next segment depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment depolarizing currents established by the influx of K+ flow down the axon and trigger an action potential at the next segment repolarizing currents established by the efflux of K+ flow down the axon and trigger an action potential at the next segment

depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment Yes! The Na+ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold.

Binding of the neurotransmitter to its receptor causes the membrane to __________. either depolarize or hyperpolarize depolarize hyperpolarize

either depolarize or hyperpolarize Yes, the neurotransmitter can cause the postsynaptic membrane to either depolarize or hyperpolarize, depending on which ion channels are opened.

In a(n) ________ synapse, current flows directly between cells

electrical, through gap junctions

Neurotransmitters exit the presynaptic cell via __________. endocytosis phagocytosis pinocytosis exocytosis

exocytosis Neurotransmitters, such as ACh, exit from vesicles that fuse with the plasma membrane of the presynaptic cell. In the case of ACh-containing vesicles, approximately 3000 neurotransmitter molecules are contained within each vesicle.

EPSPs (excitatory postsynaptic potentials) occur when hyperpolarizations occur. more potassium ions than usual leak out of a cell. chloride ions enter a cell. extra sodium ions enter a cell. more calcium ions than usual leak out of a cell.

extra sodium ions enter a cell.

What type of membrane transport causes the depolarization phase of the action potential in neurons? simple diffusion active transport filtration facilitated diffusion

facilitated diffusion Ions move through channels according to their electrochemical gradient from one side of the membrane to the other. This movement is known as channel-mediated diffusion. The transport rate for channels, unlike that for the carrier proteins involved in facilitated diffusion, does not saturate when the electrochemical gradient for the diffusing ion is increased.

Which of the following is the most important excitatory neurotransmitter in the brain? noradrenaline gamma aminobutyric acid glutamate glycine serotonin

glutamate

In saltatory propagation, a local current produces a(n): repolarization. graded depolarization. hyperpolarization. resting potential.

graded depolarization.

Regions of the CNS where neuron cell bodies dominate constitute the ________ matter.

gray

In contrast to the internodes of a myelinated axon, the nodes __________. are wrapped in myelin have higher membrane resistance to ion movement have lower membrane resistance to ion movement only occur at the beginning and end of the axon

have lower membrane resistance to ion movement In a myelinated axon, action potential regeneration occurs at the nodes where myelin is absent. Here, the ion channels associated with the action potential provide a low resistance pathway for ions to cross the axon membrane. In contrast, the myelin surrounding the internode regions makes it difficult for ions to cross the membrane. Therefore, membrane resistance at the internodes is higher than membrane resistance at the nodes. Conversely, membrane resistance at the nodes is lower than membrane resistance at the internodes.

In a typical undisturbed cell, the extracellular fluid (ECF) contains high concentrations of sodium ions and chloride ions, whereas the cytosol contains ______. high concentrations of potassium ions and negatively charged proteins high concentrations of potassium ions and low concentrations of sodium ions low concentrations of potassium ions and high concentrations of chloride ions low concentrations of potassium ions and negatively charged proteins

high concentrations of potassium ions and negatively charged proteins

Compared to the electrical gradient for sodium at rest, the electrical gradient for potassium at rest is __________. in the same direction but of lesser magnitude. in the opposite direction but of the same magnitude. in the same direction and of the same magnitude. in the same direction but of greater magnitude.

in the same direction and of the same magnitude. The electrical gradients for both potassium and sodium are inward because these positively charged ions are both attracted to the negatively charged interior of the cell. Because sodium and potassium each carry a single positive charge, the transmembrane potential affects them the same. The electrical gradient is entirely independent of the chemical gradient or the absolute concentrations of the ions

Where is acetylcholinesterase (AChE) primarily located? in synaptic vesicles in the presynaptic cell in the postsynaptic cell in the synaptic cleft

in the synaptic cleft AChE degrades acetylcholine to terminate synaptic activity. To degrade or hydrolyze ACh, AChE must also be located in the synaptic cleft. The speed at which this occurs (<20 msec) allows synaptic activity to be finely controlled.

Voltage-gated sodium channels have both an activation gate and a(n) ________ gate. ion swinging repolarization threshold inactivation

inactivation

Action potential propagation begins (is first generated at) what region of a neuron? node dendrite myelin initial segment

initial segment Graded potentials created in the dendrites and soma will, if sufficiently depolarizing, generate an action potential in the initial segment of the axon. The action potential will then propagate away from this region, down the axon.

n what part of the neuron does the action potential typically initiate? dendrites soma (cell body) axon terminals initial segment of the axon

initial segment of the axon The initial segment has the lowest threshold and, therefore, is the place where most action potentials are initiated.

If the permeability of a resting axon to sodium ion increases, the membrane potential will depolarize. outward movement of sodium ion will decrease. inward movement of sodium ion will increase. the membrane potential will hyperpolarize. inward movement of sodium ion will increase and the membrane potential will depolarize.

inward movement of sodium ion will increase and the membrane potential will depolarize.

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. the receiving neuron becomes more positive inside. vesicles in the synaptic terminal fuse to the plasma membrane of the sending neuron. ion channels in the plasma membrane of the sending neuron open. the receiving neuron becomes more negative inside.

ion channels in the plasma membrane of the receiving neuron open.

Ion channels that are always open are known as mechanically-gated channels. chemically gated channels. leak channels. voltage-gated channels. active channels.

leak channels.

Extensive damage to oligodendrocytes in the CNS could result in loss of sensation and motor control. decreased production of cerebrospinal fluid. a breakdown of the blood-brain barrier. loss of the structural framework of the brain. inability to produce scar tissue at the site of an injury.

loss of sensation and motor control.

Graded potentials are often all-or-none. produce an effect that spreads actively across the membrane surface without diminishing. always cause repolarization. may be either a depolarization or a hyperpolarization. produce an effect that increases with distance from the point of stimulation.

may be either a depolarization or a hyperpolarization.

The sodium-potassium ion exchange pump depends on a hydrogen gradient for energy. transports sodium ions into the cell during depolarization. moves sodium and potassium opposite to the direction of their electrochemical gradients. is not involved in producing the resting membrane potential. transports potassium ions out of the cell during repolarization.

moves sodium and potassium opposite to the direction of their electrochemical gradients.

The most abundant class of neuron in the central nervous system is anaxonic. unipolar. pseudopolar. bipolar. multipolar.

multipolar

The presence of ________ dramatically increases the speed at which an action potential moves along an axon.

myelin

The basic functional unit of the nervous system is the ________.

neuron

A molecule that carries information across a synaptic cleft is a neurotransmitter. synaptic cleft. synapse. sending neuron. receiving neuron

neurotransmitter Neurotransmitter molecules carry information across a synaptic cleft.

Continuous propagation: occurs along unmyelinated axons. involves nodes. begins when the transmembrane potential hyperpolarizes to -70 mV. is faster than saltatory propagation.

occurs along unmyelinated axons.

The nervous tissue outside of the central nervous system composes the ________ nervous system. peripheral

peripheral

What causes repolarization of the membrane potential during the action potential of a neuron? potassium efflux (leaving the cell) sodium influx (entering the cell) sodium efflux (leaving the cell) potassium influx (entering the cell)

potassium efflux (leaving the cell) Positively charged potassium ions flowing out of the cell makes the transmembrane potential more negative, repolarizing the membrane towards the resting potential.

In a synapse, neurotransmitters are stored in vesicles located in the __________. postsynaptic neuron synaptic cleft presynaptic neuron

presynaptic neuron Yes, neurotransmitters are stored in the axon terminals of the presynaptic neuron.

After acetylcholinesterase acts, the synaptic knob reabsorbs the acetylcholine. reabsorbs the acetate. reabsorbs the choline. all of the above none of the above

reabsorbs the choline.

The period during which an excitable membrane can respond again, but only if the stimulus is greater than the threshold stimulus, is the ________.

relative refractory period

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________. local propagation saltatory propagation myelinated propagation continuous propagation

saltatory propagation Saltatory propagation is derived from the Latin word saltare, which means leaping.

Hyperpolarization results from __________. fast closing of voltage-gated K+ channels slow closing of voltage-gated K+ channels slow closing of voltage-gated Na+ channels

slow closing of voltage-gated K+ channels the slow closing of the voltage-gated K+ channels means that more K+ is leaving the cell, making it more negative inside.

When ACh receptors open, what ion causes depolarization of the postsynaptic membrane? sodium calcium ACh potassium

sodium Positively charged sodium ions cross the postsynaptic membrane through open ACh receptors. This causes depolarization""the inside of the postsynaptic cell becomes less negative relative to the outside. If the depolarization is sufficient for the postsynaptic neuron to reach threshold, an action potential will be generated.

The movement of what ion is responsible for the local currents that depolarize other regions of the axon to threshold? voltage-gated sodium (Na+) channels Potassium (K+) sodium (Na+) calcium (Ca2+)

sodium (Na+) Sodium ions enter the cell during the beginning of an action potential. Not only does this (further) depolarize the membrane where those channels are located, but it also sets up local currents that depolarize nearby membrane segments. In the case of myelinated axons, these local currents depolarize the next node, 1-2 mm away.

The buildup of depolarization when EPSPs arrive at several places on the neuron is called ________ summation.

spatial

The site of intercellular communication between neurons is the collateral. synaptic knob. telodendria. hillock. synapse.

synapse

The small space between the sending neuron and the receiving neuron is the synaptic terminal. neurotransmitter. synaptic cleft. vesicle. calcium channel.

synaptic cleft. The synaptic cleft is the small space between the sending neuron and the receiving neuron.

The buildup of depolarization when EPSPs arrive in rapid succession is called ________ summation.

temporal

When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what occurs? hyperpolarization temporal summation decrease in speed of impulse transmission inhibition of the impulse spatial summation

temporal summation

If the sodium-potassium pumps in the plasma membrane fail to function, all of the following occur, except the inside of the membrane will have a resting potential that is more positive than normal. the intracellular concentration of sodium ions will increase. the membrane will slowly lose its capacity to generate action potentials. the neuron will slowly depolarize. the intracellular concentration of potassium ions will increase.

the intracellular concentration of potassium ions will increase.

The repolarization phase of an action potential results from __________. the opening of voltage-gated K+ channels the closing of voltage-gated Na+ channels the closing of voltage-gated K+ channels the opening of voltage-gated Na+ channels

the opening of voltage-gated K+ channels as the voltage-gated K+ channels open, K+ rushes out of the cell, causing the membrane potential to become more negative on the inside, thus repolarizing the cell.

If a signal from a sending neuron makes the receiving neuron more negative inside, the sending neuron becomes more positive inside. the receiving neuron is more likely to generate an action potential. the receiving neuron immediately generates an action potential. the sending neuron becomes more negative inside. the receiving neuron is less likely to generate an action potential.

the receiving neuron is less likely to generate an action potential. If the receiving neuron is more negative inside, it is less likely to generate an action potential.

In a neuron, sodium and potassium concentrations are maintained by the sodium-potassium exchange pump such that __________. both sodium and potassium concentrations are higher outside the cell compared to inside. 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. the concentration of sodium outside the cell is equal to the concentration of potassium inside the cell. the sodium concentration is higher inside the cell than outside the cell and the potassium concentration is higher outside the cell than inside the cell.

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 Because the sodium-potassium exchange pump moves sodium and potassium ions in opposite directions, the pump generates concentration gradients for these ions that are opposite in direction. The opposite direction of these concentration gradients explains why the equilibrium potentials for those ions are opposite in sign (that is, -90 mV for potassium and +66 mV for sodium).

What is the electrochemical gradient of an ion? the sum of the electrical and chemical gradients for that ion The electrochemical gradient is the direction an ion would diffuse (either outward or inward) when the neuron is at rest, regardless of the transmembrane potential. the difference between the concentrations of an ion inside and outside the cell the transmembrane potential at which the electrical and chemical gradients are equal in magnitude, but opposite in direction

the sum of the electrical and chemical gradients for that ion Correct Together, these two gradients determine the net movement of a particular ion across the plasma membrane.

During an action potential of a neuron, what directly causes the different channels to open and close? Sodium and potassium ions neurotransmitter binding to chemically gated channels the transmembrane potential (voltage) calcium ions

the transmembrane potential (voltage) Changes in transmembrane potential directly cause voltage-gated channel proteins to change shape and allow the flow of ions across the cell membrane. The tiny electrical current associated with a single channel opening can actually be measured with sensitive recording techniques.

When calcium ions enter the synaptic terminal, the inside of the receiving neuron becomes more positive. they cause an action potential in the sending neuron. they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron. the inside of the receiving neuron becomes more negative. neurotransmitter molecules are quickly removed from the synaptic cleft.

they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

Sensory neurons of the PNS are unipolar. anaxonic. tripolar. bipolar. multipolar.

unipolar

Neurotransmitter for release is stored in synaptic telodendria. knobs. neurosomes. mitochondria. vesicles.

vesicles

A gated channel that responds to changes in transmembrane potential is called a ________ gated channel.

voltage

An action potential releases neurotransmitter from a neuron by opening which of the following channels? voltage-gated K+ channels voltage-gated Ca2+ channels voltage-gated Na+ channels chemically gated Ca2+ channels

voltage-gated Ca2+ channels Yes, opening of these channels causes calcium to move into the axon terminal. Calcium inside the neuron causes the vesicles to merge with the membrane and release the neurotransmitter via exocytosis into the synaptic cleft.

The depolarization phase of an action potential results from the opening of which channels? voltage-gated K+ channels chemically gated Na+ channels chemically gated K+ channels voltage-gated Na+ channels

voltage-gated Na+ channels when the voltage-gated Na+ channels open, Na+ rushes into the cell causing depolarization.

What is primarily responsible for the brief hyperpolarization near the end of the action potential? the sodium/potassium exchange pump taking some time to restore the normal ion concentrations voltage-gated sodium channels taking some time to recover from inactivation voltage-gated potassium channels taking some time to close in response to the negative membrane potential voltage-gated potassium channels opening as the membrane potential becomes more negative (repolarized)

voltage-gated potassium channels taking some time to close in response to the negative membrane potential Although both types of voltage-gated channels open and close in response to changes in membrane voltage, the voltage-gated potassium channels open and close much more slowly than the voltage-gated sodium channels. This slowness means that voltage-gated potassium channels do not immediately close after the resting potential (-70 mV) is reached. Instead, they drag the membrane potential briefly towards the potassium equilibrium potential (-90 mV).