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258: Physiology > Lecture 2: Membrane and action potentials > Flashcards

Lecture 2: Membrane and action potentials Flashcards

1
Q

Does Na+ want to flow into the cell or outside?

A

Wants to flow inside the cell

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2
Q

Does K+ want to flow inside the cell or outside

A

outisde

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3
Q

What is the definition of Resting Membrane Potential (Vm)

A

Electical potential difference across the membrane

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4
Q

What do you call it when you there is a potential difference across the membrane?

A

POLARIZED

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5
Q

What would happen if the membrane was ONLY permeable to K+/Na+

A

K+/Na+ would diffuse down its concentration gradient until the electrical potential (diffusion potential) across the membrane counters the K+ diffusion

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6
Q

If membrane was only permeable to K+, when would diffusion stop?

A

When the concentration difference=electrical difference

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7
Q

What is another name for NERST potential?

A

equilibrium potential?

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8
Q

Define Nerst Potential (equilibirum potential)

A

the electrical (diffusion) potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane

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9
Q

What is the nerst equation

A

±61 log⁡(𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛𝑠𝑖𝑑𝑒 (𝐾𝑖)/(𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑢𝑡𝑠𝑖𝑑𝑒 (𝐾0)

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10
Q

How do you determine the sign for the nerst potential equation?

A

-The sign of the potential is positive if the ion diffusing is negative
and it is negative if the ion is positive

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11
Q

The electrical potential that counters net diffusion of Na+ is called…

A

The Na+ equilibrium potential OR

Nerst potential for Na+

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12
Q

What does the Goldman ( Goldman-Hodgkin-Katz ) equation assess

A

Equilibrium Potential of Membrane Permeable to Several Different Ions

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13
Q

What 3 factors does the Goldman ( Goldman-Hodgkin-Katz ) equation depend on?

A

1) CONCENTRATION: of respective ions on the inside (i) and outside (o) of the membrane

2) PERMEABILITY: of membrane (P) to each ion
3) polarity of the electrical charge of ions positive or negative

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14
Q

Why is the resting membrane potential so close to the equlibrium potential for K+ in comparison to Na+

A

The membrane is far more permeable to K+ than to Na+

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15
Q

What is the equlibrium potential for na+ and k+

A 
na+= 61 mV
K+= -94mV
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16
Q

What are the 2 Transport Properties of Resting Nerve Membrane

A

1) Leak channels much more permeable to K+ than Na+ (~ 100 times)
2) Na+/K+ pump: Net increase of 1 positive charge outside: More Negativity inside

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17
Q

What is the resting membrane potential for large nerve fibers? for small neurons?

A
  • 90mV for large nerve fibers (e.g. motoneurons)

- 70 mV for small neurons of nervous system

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18
Q

Resting membrane potential of nerves depends on what 3 factors?

A
  1. Diffusion of potassium and sodium ions (K+ : Inside to Outside,
    Na+: Outside to Inside (less degree)
  2. Permeability of ions through leak channels
    P to K+&raquo_space; P to Na+ (~ 100 times).
  3. Na+/K+ Pump
    Creates more negativity inside (transports 3 Na+ ions to outside vs 2 K+ ions to inside).
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19
Q

The resting membrane potential is closer to the equilibrium potential for the ion with the BLANK permeability (i.e. K+).

A

HIGHEST PERMEABLITY

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20
Q

What is action potential?

A

AP is a very rapid change in the membrane potential from “-“ to “+“ values and return back to initial resting potential level

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21
Q

True or false and explain: AP is an all or nothing event?

A

TRUE: either it occurs fully or it does not occur at all (amplitude of AP never change)

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22
Q

Where does AP propagate

A

along nerve fiber until it comes to the end of the fiber

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23
Q

What are the 3 functions of AP

A

1) transmitting nerve signals
2) rapid transmission over distance
3) encoding information (neuronal language)

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24
Q

Explain the 3 functions of AP

A

1) Transmitting nerve signals

  • Transfer all sensory information from the periphery to central nervous system (CNS)
  • Transfer all motor information from CNS to periphery (e.g. muscles, endocrine system…etc)
  • Transfer information between different parts of CNS

2) Rapid Transmission over distance
Note: speed of transmission (conduction velocity) depends on fiber size (how big the axon is) and whether it is myelinated

3) Encoding Information (neuronal language)
- The frequency of APs encodes information

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25
Q

What does speed of transmission of AP depend on?

A

depends on fiber size (how big the axon is) and whether it is myelinated

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26
Q

In which of these examples the AP will travel at the highest speed?

a) Twisting your ankle…ouch! It hurts!!!
b) Feeling the position of my limbs in space
c) Feeling a pressure on my skin

A

Feeling the position of my limbs in space

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27
Q

What encodes information? the frequency or the amplitude of the AP

A

THE FREQUENCY

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28
Q

What are the 5 sequence of events for AP

A

1) resting state
2) depolarization
3) repolarization
4) undershoot
5) back to resting

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29
Q

be able to identify the sequence of events for Ap on a diagram

A

/

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30
Q

Explain resting stage of nerve AP

A

-90 mV, membrane is balanced

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31
Q

Explain depolarization state

A

-90 to 35 mV
0.1 ms period (very rapid)
Caused by sudden opening of Na+ channels, Na+ ions flow to inside the cell

32
Q

explain repolarization

A

+35 to -90 mV
Na+ channels begin to close, Na+ ions stop to flow inside,

K+ channels open slowly.
K+ ions start to flow outside
Re-establish negative resting potential

33
Q

explain “overshoot” of AP

A

Overshoot occurs because some Na+ will still get in the membrane after the channels close
(goes from 0-35 because while the gate is closing a few ions will still come through)

34
Q

explain afterpotential (undershoot)

A

Less than -90 mv

Caused by K+ channels that remain open for few milliseconds after repolarization of membrane is completed.

35
Q

explain back to resting stage

A

closing of K+ channels

36
Q

What causes the different stages of action potential

A

Different stages of the action potential are due to the activation of two special types of protein channels on the nerve membrane
voltage gated Na+ and K+ channels

37
Q

What are the 2 protein channels on the nerve membrane that affect AP

A

Voltage-gated Na+ channels

Voltage-gated K+ channels

38
Q

Does voltage gated channels open due to simple diffusion?

A

yes, sensitive to change in membrane potential

39
Q

What are the 2 gates of the sodium gated channel and where are they located

A

activation gate: exterior

inactivation gate: interior

40
Q

What are the 3 states of the gated sodium channels?

A

Resting state: Activation closed and inactivation open

Activated state: Both open (depolar)

Inactivated state
Activation open and inactivation closed (sodium stops entering the cell)

41
Q

Explain resting state of voltage gated sodium channels

A

Activation gate is closed
Inactivation gate is open
No entering of Na+ ions

42
Q

explain activated state (depolarization)

A

Sudden opening of activation gate is triggered by the shifting of membrane potential towards + values

Opening threshold: between -70 and -50 mV
Permeability to Na+ increases to 500 to 5000 times

Sodium ions flow inside (MASSIVE FLOW OF Na+)

43
Q

What is the opening threshold for the sodium gated channel

A

between -70 to -50

44
Q

True or false: when in activated state, the permiability to sodium increases?

A

TRUE

45
Q

explain inactivated state

A

Inactivation gate is activated when membrane potential increases above 0 mV (overshoot).
Na+ ions stop to flow inside and the membrane potential recovers back toward resting state

Inactivation gates do not re-open until membrane returns to resting potential (Refractory Period)

46
Q

Where is the gate for the gated potassium channel?

A

one gate in the interior of the membrane

47
Q

What are the 2 states of the gated potassium channel

A

Resting state

Slow activation state

48
Q

explain the resting state

A

GATE IS CLOSED

49
Q

explain the slow activation state (repolarization)

A
  • K+ channels are activated when membrane potential increases above 0 mV (overshoot)
  • Gates open slowly at the same time when Na+ channels (inactivation gates) begin to close

-Potassium ions flow outside
It accelerates repolarization toward resting potential

50
Q

Explain undershoot

A

K+ channels remain open for few milliseconds after repolarization of membrane is completed.

Excess K+ ions flow out of cell

51
Q

Because of the function that mirror neurons play, Dr. Ramachandran referred to them as:

A

empathy neurons

52
Q

explain threshold for initiation

A

Threshold is the level of membrane potential at which the positive-feedback cycle is created (point of no return)

53
Q

When does the threshold occur for AP

A

Occurs when the number of sodium ions entering the nerve becomes greater than the number of potassium ions leaving the nerve (want membrane to become less negative)
~ - 65 mv for a Nerve with Vm = -90 mV

54
Q

what are the 3 causes for initial increase of membrane potential

A

1) Electrical stimulation
2) Mechanic stimulation
3) Chemical stimulation

55
Q

The amplitude of an AP is ________________ of the intensity of the stimulus that evokes it

A

INDEPENDANT

56
Q

The frequency of firing (number of APs) is ____________ on the intensity of the stimulus.

A

.DEPENDANT

57
Q

explain absolute refractory period and why

A

Period during which a new AP cannot occur as long as the membrane is still depolarized from the preceding AP

WHY:

  • Na+ channels are inactivated
  • Membrane has to return to near original resting potential to allow inactivation gates to reopen
58
Q

explain relative refractory period

A

Period that follows the AbsoluteRefractory Period during which a new AP can occur in response to a strong stimulus (greater than normal

why:
- Some Na+ channels start to go back to resting state and others are still inactivated
- K+ channels are still open and the membrane is hyperpolarized (during the undershoot)

59
Q

why can you not generate new AP in absolute refractory period?

A

Na+ channels are inactivated

-Membrane has to return to near original resting potential to allow inactivation gates to reopen

60
Q

explain why you can generate AP during the relative refractory period

A
  • Some Na+ channels start to go back to resting stae and others are still inactivated
  • K+ channels are still open and the membrane is hyperpolarized (during the undershoot)
61
Q

what is the axon surrounded by

A

myelin sheaths

62
Q

what is myeline produced as an extension of what cells>

A

Myelin is produced as an extension of particular cells (glial cells):
Schwann cells (in peripheral nervous system)
Oligodendrocytes (central nervous system

63
Q

where do you find shwann cells?

A

peripheral nervous system

64
Q

where do you find oligodendrocytes ?

A

CNS

65
Q

Where does propogation of AP occur

A

myelinated nerve fibers

66
Q

Can ions flow significantly through the myelin sheath

A

Ions cannot flow significantly through thick myelin sheath, which thus insulates nerve fibers.

67
Q

About once every 1-3 mm, myelin sheath is interrupted by …

A

interrupted by a node of Ranvier

68
Q

what are the two types of neuron fibers

A

myelinated and unmyelinated

69
Q

Explain saltatory conduction

A

APs can only occur at the nodes of Ranvier and are conducted from node to node.

Saltatory conduction conserves energy for axon (little metabolism required to re-establish ionic concentration differences)

Conduction velocity varies from little as 0.25 m/s in unmyelinated fibers to as great as 120 m/s in large myelinated fiber

70
Q

where are voltage gates channels found?

A

nodes of ranvier

71
Q

what are the difference in conduction velocities of myelinated vs unmyelinated?

A

.Conduction velocity varies from little as 0.25 m/s in unmyelinated fibers to as great as 120 m/s in large myelinated fiber

72
Q

explain propagration of AP on unmyelinated fibers

A

Action potential excites adjacent portions of membrane, resulting in propagation of the action potential.

Na+ ions flow to adjacent area:
Increase voltage of adjacent area to threshold level.
Initiate adjacent action potential

0.25 ms

73
Q

be able to identify propagation visuals

A

..

74
Q

what is MS and some symptoms of it

A

MS is an immune-mediated inflammatory disease that causes the demyelination of the central nervous system.

Muscle weakness
Loss of sensation
Death

75
Q

what does MS cause?

A

conduction blockage

258: Physiology (25 decks)

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