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z:2017 - Biosci 107 2/2 > Neurons Mastering AP quiz > Flashcards

Neurons Mastering AP quiz Flashcards

1
Q

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?

A

Resting membrane potential (RMP)

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2
Q

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

A

Leak channels

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3
Q

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

A

The inside surface of the plasma membrane is much more negatively charged than the outside surface

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4
Q

The plasma membrane is much more permeable to K+ than to Na+. Why?

A

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

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5
Q

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. What are these two factors.

A

The presence of concentration gradients and leak channels

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6
Q

What prevents the Na+ and K+ gradients from dissipating?

A

Na+-K+ ATPase

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7
Q

he membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____. What does this help do inside the cell?

A

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

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8
Q

During depolarization, which gradient(s) move(s) Na+ into the cell?

A

both the electrical and chemical gradients

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9
Q

What is the value for the resting membrane potential for most neurons?

A

-70mV

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10
Q

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?

A

Na+ is pumped out of the cell and K+ is pumped into the cell.

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11
Q

The concentrations of which two ions are highest outside the cell.

A

Na+ and Cl–

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12
Q

In a neuron, sodium and potassium concentrations are maintained by the sodium-potassium exchange pump such that __________.

A

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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13
Q

The sodium-potassium exchange pump transports potassium and sodium ions in which direction(s)?

A

Sodium ions are transported out of the cell. Potassium ions are transported into the cell.

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14
Q

Leak channels allow the movement of potassium and sodium ions by what type of membrane transport? What is this membrane transport mechanism called and how is it worked??

A

channel-mediated diffusion <> Leak channel via the electrochemical gradient

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15
Q

The electrochemical gradient for potassium ions when the transmembrane potential is at the resting potential (-70 mV) is caused by what?

A

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

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16
Q

What is the electrochemical gradient of an ion?

A

the sum of the electrical and chemical gradients for that ion

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17
Q

In a typical neuron, what is the equilibrium potential for potassium? Why is it this number?

A

-90mV <> 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.

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18
Q

The electrochemical gradient for sodium ions in a neuron when the transmembrane potential is at the resting potential is caused by what?

A

chemical and electrical gradients both going into the cell

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19
Q

Compared to the electrical gradient for sodium at rest, the electrical gradient for potassium at rest is __________. Why is this?

A

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.

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20
Q

In a typical neuron, what is the equilibrium potential for sodium? Why this value?

A

+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.

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21
Q

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)?

A

The membrane is much more permeable to potassium ions than to sodium ions.

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22
Q

Where do most action potentials originate?

A

Initial segment

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23
Q

What is the initial segment? Where is it? What is it also called?

A

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.

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24
Q

What opens first in response to a threshold stimulus?

A

Voltage-gated Na+ channels

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25
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
26
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.
27
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.
28
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
29
How does the speed of the activation gates of Na+ and K+ compare?
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.
30
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels
31
The repolarization phase of an action potential results from \_\_\_\_\_\_\_\_\_\_.
the opening of voltage-gated K+ channels
32
Hyperpolarization results from \_\_\_\_\_\_\_\_\_\_.
slow closing of voltage-gated K+ channels
33
How does hyperpolarization make the cell more polar?
the slow closing of the voltage-gated K+ channels means that more K+ is leaving the cell, making it more negative inside.
34
What is the magnitude (amplitude) of an action potential? What is the range?
100mV \<\> -70mV to 30mV
35
During an action potential of a neuron, what directly causes the different channels to open and close?
the transmembrane potential (voltage)
36
What is the typical duration of a nerve action potential?
2ms
37
Around what transmembrane potential does threshold commonly occur? What happens at this voltage?
-60mV \<\> an action potential is initiated
38
What ion is responsible for the depolarization of the neuron during an action potential? What does it do to make this depolarisation possible?
Na+ \<\> The influx of sodium ions causes the rapid depolarization during the action potential.
39
What factors favour the influx of sodium ions through open channel?
(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.
40
What type of membrane transport causes the depolarization phase of the action potential in neurons? What type of movement is this?
facilitated diffusion \<\> Channel-mediated diffusion
41
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.
42
What causes repolarization of the membrane potential during the action potential of a neuron? Why does this cause repolarisation?
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.
43
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
44
Label the diagram
45
What do action potential depend on?
Voltage gated channels
46
Describe the all-or-none principle
All stimuli that bring the membrane to threshold generate identical action potentials.
47
Which one of these occurs correspondingly? Potassium channels close; –60 mV Depolarization to threshold; +10 mV Resting potential; +30 mV Inactivation of sodium channels; +30 mV
Inactivation of sodium channels; +30 mV
48
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent area.
49
Why does the action potential only move away from the cell body? Why is this?
The areas that have had the action potential are refractory to a new action potential. \<\> sodium channels are inactivated in the area that just had the action potential.
50
Where are action potentials regenerated as they propagate along an unmyelinated axon?
at every segment of the axon
51
The movement of what ion is responsible for the local currents that depolarize other regions of the axon to threshold? How does it work?
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.
52
In an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction? What causes this behaviour?
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.
53
Approximately how fast do action potentials propagate in unmyelinated axons in humans?
1 meter per second
54
In contrast to the internodes of a myelinated axon, the nodes \_\_\_\_\_\_\_\_\_\_.
have lower membrane resistance to ion movement
55
Where are action potentials regenerated as they propagate along a myelinated axon? Why here?
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.
56
The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called \_\_\_\_\_\_\_\_\_\_.
saltatory propagation
57
How do action potential propagation speeds in myelinated and unmyelinated axons compare?
Propagation is faster in myelinated axons.
58
What is it about myelinated axons that allows them to transmit information fast?
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.
59
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.
60
Why does demyelination stop action potential propagation in multiple sclerosis?
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.
61
What type of conduction takes place in unmyelinated axons?
Continuous conduction
62
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
63
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.
64
When do the inactivation gates close? What does this result in?
At the peak of the depolarization phase of the action potential, the inactivation gates close. \<\> The voltage-gated Na+‎ channels become absolutely refractory to another depolarizing stimulus.
65
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.
66
How does myelin increase the speed of action potential conduction? What does this mean of the regeneration?
1 - myelin insulates the axon, reducing the loss of depolarizing current across the plasma membrane. \<\> 2 - 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.
67
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.
68
What is the closing of voltage gate channels dependent on? Explain how they timing influence the activation/deactivation of gates
Time \<\> 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.
69
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
70
How does the myelinated and diameter of a axon influence velocity?
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.
71
The small space between the sending neuron and the receiving neuron is the
synaptic cleft.
72
A molecule that carries information across a synaptic cleft is a
neurotransmitter
73
When calcium ions enter the synaptic terminal,
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
74
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.
75
If a signal from a sending neuron makes the receiving neuron more negative inside,
If a signal from a sending neuron makes the receiving neuron more negative inside,
76
In a synapse, neurotransmitters are stored in vesicles located in the \_\_\_\_\_\_\_\_\_\_.
presynaptic neuron
77
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
voltage-gated Ca2+ channels
78
How does the opening of the voltage gated Ca2+ channel causes an action potential release to release neurotransmitter?
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
79
Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.
chemically gated; postsynaptic
80
Binding of the neurotransmitter to its receptor causes the membrane to \_\_\_\_\_\_\_\_\_\_. What determines this?
either depolarize or hyperpolarize \<\> the neurotransmitter can cause the postsynaptic membrane to either depolarize or hyperpolarize, depending on which ion channels are opened
81
The mechanism by which the neurotransmitter is returned to a presynaptic neuron’s axon terminal is specific for each neurotransmitter. Which neurotransmitters is broken down by an enzyme before being returned?
acetylcholine
82
What causes calcium channels in the synaptic knob to open?
depolarization of the presynaptic membrane due to an arriving action potential q
83
Which of the following best describes the role of calcium in synaptic activity?
Calcium enters the presynaptic cell and causes the release of ACh.
84
Explain what happens when a presynaptic action potential reaches the synaptic terminal. How long does it take for activation?
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. \<\> 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.
85
Neurotransmitters exit the presynaptic cell via \_\_\_\_\_\_\_\_\_\_.
exocytosis
86
How many neurotransmitter containers within each vesicle?
3000
87
The acetylcholine receptor is an example of what type of channel?
Chemical gated channel
88
When ACh receptors open, what ion causes depolarization of the postsynaptic membrane? How does this work?
Na \<\> 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.
89
Describe how ACh causes depolarization of the postsynaptic membrane?
ACh opens ACh receptors.
90
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.
91
What is the primary role of acetylcholinesterase (AChE) at a cholinergic synapse?
AChE degrades acetylcholine in the synaptic cleft.
92
Where is acetylcholinesterase (AChE) primarily located?
in the synaptic cleft
93
Describe the order of event in synaptic activity
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.
94
Regions of the CNS where neuron cell bodies dominate constitute the ________ matter.
Grey matter
95
The most abundant class of neuron in the central nervous system is
Multipolar
96
Branches that may occur along an axon are called
collaterals
97
The site of intercellular communication between neurons is the
Synapse
98
Neurotransmitter for release is stored in synaptic....
Vesicles
99
Sensory neurons of the PNS are what kind of neuron?
Unipolar
100
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
101
If the potassium permeability of a resting neuron increases above the resting permeability, what effect will this have on the transmembrane potential?
The inside of the membrane will become more negative.
102
If the permeability of a resting axon to sodium ion increases, what would happen?
inward movement of sodium ion will increase and the membrane potential will depolarize.
103
Ion channels that are always open are known as
Leak channels
104
How can ions move across the plasma membrane?
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
105
A shift of the resting transmembrane potential toward 0 mV is called \_\_\_\_\_\_\_\_.
Depolarisation
106
What can Graded potentials be?
may be either a depolarization or a hyperpolarization.
107
Opening of sodium channels in the axon membrane causes...
both depolarization and increased positive charge inside the membrane.
108
Raising the potassium ion concentration in the extracellular fluid surrounding a nerve cell will have which effect?
depolarize it
109
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...
4, 6, 7, 1, 2, 3, 5.
110
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
111
How would the absolute refractory period be affected if voltage-regulated sodium channels failed to inactivate?
It would last indefinitely.
112
The all-or-none principle states that
all stimuli great enough to bring the membrane to threshold will produce identical action potentials.
113
Puffer fish poison blocks voltage-gated sodium channels like a cork. What effect would this neurotoxin have on the function of neurons?
The axon would be unable to generate action potentials.
114
Extensive damage to oligodendrocytes in the CNS could result in
loss of sensation and motor control.
115
What kind and type of nerve component does Continuous propagation occur in?
occurs along unmyelinated axons.
116
What happens 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, and local currents depolarize the region just adjacent to the active zone.
117
In saltatory propagation, a local current produces...
Graded depolarisation
118
What kind of channel open or close in response to physical distortion of the membrane surface?
Mechanically gated
119
What kind of channels open or close in response to binding specific molecules?
Chemically gated channel
120
Label the steps
121
Which of the following is defined as a graded hyperpolarization of the postsynaptic membrane?
IPSP
122
When does EPSPs (excitatory postsynaptic potentials) occur?
When extra sodium ions enter a cell.
123
What are IPSPs (inhibitory postsynaptic potentials)?
graded hyperpolarizations.
124
What is the most important excitatory neurotransmitter in the brain?
glutamate
125
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.
126
What is the ion that triggers the release of acetylcholine into the synaptic cleft is
Calcium
127
What is the sequence of events that occur at a cholinergic synapse?
1 - An arriving action potential depolarizes the synaptic knob. \<\> 2 - ACh is released through the exocytosis of synaptic vesicles. \<\> 3- ACh binds to sodium channel receptors. \<\> 4 - ACh is broken down by AChE. \<\> 5 - The synaptic knob reabsorbs choline from the synaptic cleft.
128
What has an effect on synaptic function?
interfering with neurotransmitter synthesis \<\> preventing neurotransmitter inactivation \<\> blocking neurotransmitter binding to receptors \<\> interfering with neurotransmitter reuptake
129
What does Spatial summation involve?
multiple synapses that are active simultaneously.
130
Where is the site of the neuron where EPSPs and IPSPs are integrated?
axon hillock.
131
When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what occurs?
Temporal summation
132
What is the buildup of depolarization when EPSPs arrive at several places on the neuron is called?
Spatial summation

z:2017 - Biosci 107 2/2 (16 decks)

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