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Muscle/nerves (F&F) > Membrane Potential/Action Potential/Graded Potential > Flashcards

Membrane Potential/Action Potential/Graded Potential Flashcards

1
Q

What is a membrane potential?

A
  • The electrical charge difference across the cell membrane.
  • Measured in millivolts (mV)
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2
Q

Excitable vs. non-excitable tissues

A

Excitable- generally a more negative resting membrane potential
-70 to -90 mV

Non-excitable- Have less negative resting membrane potential
-53 mV in epithelial cells
-8.4 mV in RBC
-20 to -30 mV in fibroblasts
-58 mV in adipocytes

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3
Q

Polarity of cells

A

Inside is more negatively charged relative to outside

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4
Q

How is resting membrane potential established and maintained?

A
  1. Unequal ionic distributions
  2. Differences in membrane permeability to Na+ and K+ (Role of leaky channels)
  3. Active transport: Na/K pump
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5
Q

Unequal ionic distributions

A
  • More Na+ and Cl- outside the cell
  • More K+ inside the cell
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6
Q

Differences in membrane permeability to Na+ and K+

A
  • Cells contain many more K+ leaky channels
  • Cells contain 1/100th x less Na+ leaky channels
  • More K+ leaving the cell than Na+ entering the cell
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7
Q

Active Transport: Na+/K+

A
  • The Na/K pump will transport 3 Na+ outside the cell, and 2 K+ inside the cell
  • Overall, generates a net negative charge inside the cycle
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8
Q

What cells can generate action potentials?

A

Only excitable cells like neuron, muscle, glands, can respond to changes in membrane potential to generate action potential

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9
Q

Changes in membrane potential

A
  1. hyperpolarization
  2. Depolarization
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10
Q

Hyperpolarization

A

When membrane potential becomes more negative than the resting membrane potential (Neuron is super relaxed)

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11
Q

Depolarization

A

When membrane potential becomes less negative than the resting membrane potential (neuron is excited)

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12
Q

Equilibrium potential

A
  • The membrane potential when there is no net flow of ions. Both concentration gradient and electrochemical gradient cancel each other out
  • All ions want to reach their equilibrium potential
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13
Q

What is the other name for equilibrium potential?

A

Nernst potential

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14
Q

Goldman-Hodgkin-Katz (GHK) Equation

A

Allows you to change the membrane permeability for a specific ion to determine total membrane potential

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15
Q

Factors that contribute to the membrane potential

A
  • Differences in concentration gradients of Na and K
  • Number of leaky channels for Na and K ions (there are more K ions)
  • Na/K pump: 3Na outside, 2K inside (moving against concentration gradient)
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16
Q

Variables of the Nernst Equation

A
  1. Temperature
  2. Concentration of K inside cell
  3. Concentration of K outside cell
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17
Q

Factors that contribute to the measured resting potential

A
  • Differences in concentration gradient
  • Na/K pump
  • Number of leaky channels
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18
Q

Factors that contribute to the equilibrium potential

A
  • Temperature
  • Difference in concentrations of K inside and outside the cell
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19
Q

Difference between membrane potential (Vm) and equilibrium potential (Ex)

A
  • Vm: physiological value; depends on the concentration difference of multiple ions and their relative permeabilities across the cell membrane
  • Ex: constant value at a specific temperature, depends only on the concentration difference of one ion across the cell membrane
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20
Q

What is the driving force for ion movement?

A

The difference between the actual membrane potential and the equilibrium potential for a specific ion (Vm-Ex)

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21
Q

Why is Fick’s law not involved in ion movement across cell membrane?

A

Fick’s law is based on uncharged particles and ion movement is based on both the concentration gradient and electrical charge

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22
Q

What is the variables in the Golden-Hodgkin-Katz (GHK) equation?

A
  • Concentration inside and outside of multiple ions (K, Na, Cl)
  • Membrane permeability of multiple ions
  • Temperature
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23
Q

Why does a change in permeability not have an effect on the concentration values?

A
  • Changing permeability does not really effect the concentration values of the ions, but it will change the membrane potential.
  • The small ion change that it does cause will be on the microscopic level.
  • Small changes are enough to generate electrical signals necessary for our cells to communicate
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24
Q

What ion has the greatest driving force at rest?

A

Na
- Permeability increases during an action potential because of the opening of a voltage-gated sodium channel

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25
Q

What causes voltage gated sodium channels to open?

A

Need a depolarizing membrane potential that reaches the minimal value= threshold

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26
Q

Equilibrium constants for Na and K

A

Na: positive equilibrium constant
K: negative equilibrium constant (less than -65mV)

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27
Q

Resting membrane potential

A

-65 mV

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28
Q

Steps of an Action potential

A
  1. Resting State
  2. Depolarization
  3. Peak of Action potential
  4. Repolarization
  5. Hyperpolarization
  6. Return to resting state
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29
Q

Resting state of action potential

A
  • Membrane is at a resting potential
  • Voltage-gated sodium and potassium channels are closed
30
Q

Depolarization stage of action potential

A
  • Triggered when the membrane potential reaches a threshold
  • Voltage-gated sodium channels open, allowing Na ions to flood into the cell
  • Membrane potential becomes more positive
31
Q

Peak of action potential

A
  • Membrane becomes close to 100mV more depolarized compared to the RMP
  • Voltage-gated sodium channels start to close (inactive)
32
Q

Repolarization stage of action potential

A
  • Voltage-gated potassium channels open, allowing K ions to exit the cell
  • Membrane potential returns toward the resting state
33
Q

Hyperpolarization of action potential

A

Some K channels remain open a bit longer, causing the membrane to dip below the resting potential

34
Q

Return to resting state during action potential

A
  • Sodium and potassium channels reset to their original states
  • The Na/K pump works to restore ion balance across the membrane
35
Q

Absolute refractory period

A
  • The time during which a second action potential is impossible to initiate, regardless of the stimulus strength
  • All voltage-gated Na channels are inactivated (due to inactivation gates)
  • Ensures one-way propagation of action potentials and sets a limit on the maximum firing frequency of the neuron
36
Q

Relative refractory period

A
  • Follows the absolute refractory period
  • A second action potential can be initiated, but it requires a stronger stimulus than usual
  • Allows for the possibility of stimulus intensity coding through variations in firing frequency
  • Ex. First AP= needs at least 3ms in between, second AP= needs 1ms in between
37
Q

Effect of stimulus strength on action potential

A
  • AP is always the same size (All of nothing) so stimulus strength does not change the amplitude of AP, but can change its frequency
  • Sustained threshold stimulus will generate a train of APs with an interval including both absolute and relative refractory periods
  • Sustained supra-threshold stimulus will generate a train of APs with an interval including only the absolute refractory period
38
Q

Why is there no way to have another action potential during the absolute refractory period?

A

All of the sodium channels are inactive and there is no way for another action potential

39
Q

What part of the neuron will the action potential be initiated?

A

The axon hillock where there are lots of voltage-gated Na channels

40
Q

Types of electrical signals in excitable cells

A
  1. Action potentials
  2. Graded potentials
41
Q

Graded potential

A
  • A local signal proportional to stimulus
  • Sub-threshold changes in membrane potential
42
Q

Where do graded potentials primarily occur?

A

Dendrites and cell body

43
Q

Graded potential characteristics

A
  • Vary in amplitude based on the duration and strength of the stimulus
  • Decremental nature: diminishes in strength over distance
44
Q

Role of graded potential in neural communication

A

Serve as the initial response to external changes

45
Q

Types of graded potentials

A
  1. Receptor potential/generator potential
  2. Postsynaptic potential
  3. Endplate potential
46
Q

Receptor potential/generator potential

A

Graded potential generated by sensory receptors at the nerve endings of the sensory neuron

47
Q

Postsynaptic potential

A

Graded potential generated by neurotransmitter binding to its receptor on the postsynaptic neuron

48
Q

Endplate potential

A

Graded potential generated by neurotransmitter binding to its receptor on the skeletal muscle fiber

49
Q

Reflex motor control sensory receptors

A

When patella tendon is tapped with reflex hammer, it causes the muscle to stretch.

This stretching opens mechanosensitive channels (many different channels within the membrane and the combination of them create a strong enough signal to pass on) that allow positive ions to flow in and generate a receptor current

50
Q

Stimulus strength vs. receptor potential size

A

Receptor potential magnitude correlates with stimulus strength. The receptor potential must reach threshold for the voltage gated Na channels to open and trigger an action potential. A high receptor potential can result in lots of action potentials but it is limited during the absolute refractory period.

These action potentials will move down motor neuron towards the muscle fiber. May need to be stronger just to reach all of the way.

51
Q

Types of postsynaptic potential

A
  1. Excitatory
  2. Inhibitory
52
Q

Inhibitory postsynaptic potential

A
  • Hyperpolarizing signal
  • Causes Cl to enter the cell
53
Q

Excitatory postsynaptic potential

A
  • Depolarizing signal (getting closer to threshold)
  • Causes Na to enter the cell
54
Q

Different summations of graded potential

A
  1. Temporal summation
  2. Spatial summation
55
Q

Temporal summation

A

Successive, rapid input from a single pre-presynaptic neuron is electrically summed

56
Q

Spatial summation

A

Simultaneous input from more than one pre-synaptic neuron is electrically summed

57
Q

Why can the action potential not be summed?

A

It is always the same size (all or nothing) because there are only so many Na channels and they are closed during the absolute refractory period

58
Q

Types of propagation of electrical signals within a neuron

A
  1. Passive spreading
  2. Active spreading
59
Q

Passive spreading

A
  • Slow and small amplitude
  • Localized
  • Signal dies off with distance
60
Q

Active spreading

A
  • Fast and large amplitude
  • Travel far
  • Signal is self-regenerated
  • Requires voltage-gated Na and K channels to be positioned along the path of propagation
61
Q

Action potential propagation

A
  • Active spreading (& some passive spreading but minimal)
  • Na will enter the cell, passively spreads and opens up nearby channel
  • Original channel will close and absolute refractory period will prevent local signalling from reopening it
  • Local signal will open the nearest channel in other direction allowing more Na to enter and further depolarization through the channels as the signal moves forward
62
Q

Distribution of Na and K channels

A

Order from greatest amount to lowest amount
1. Nodes of ranvier
2. Axon hillock
3. Soma
4. Myelinated regions
5. Axon terminal

63
Q

Myelination and AP distance of travel

A

Myelination reduces the distance that an action potential needs to travel as it allows for saltatory conduction (AP jumping from node to node)

64
Q

Factors affecting conduction speed in neurons

A
  1. Myelination
  2. Axon diameter
65
Q

Myelination and conduction speed

A
  • Myelinated neurons: faster conduction. Action potential jumps between nodes of ranvier
  • Unmyelinated neurons: continuous, slower propagation of the action potential
66
Q

Axon diameter and conduction speeds

A

Large diameter: faster conduction due to decreased resistance to the flow of electric current

Small diameter: slower conduction

67
Q

Nerve fiber classification and speed of signal propagation

A

A fibers: myelinated with large diameter= fast conduction speed

B fibers: myelinated, slightly smaller fibers that A= medium conduction speed

C fibers: unmyelinated and small= slowest conduction speed

68
Q

How are graded and action potentials triggered?

A

Graded: triggered by external stimuli or neurotransmitter release

Action: triggered by membrane depolarization to threshold due to graded potential

69
Q

Where do graded vs. action potentials occur?

A

Graded: any region of the membrane

Action: only in membrane with a high concentration of voltage-gated Na and K channels

70
Q

What kind of channels are needed for action vs. graded potentials?

A

Graded: any ion channels (ligand-gated, mechano or temp sensitive, etc)

Action: Voltage-gated Na and K channels

Muscle/nerves (F&F) (9 decks)

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