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Exam 1 > Electrical Properties of Cells > Flashcards

Electrical Properties of Cells Flashcards

Exam 1, FOM 1, Lecture 18

1
Q

What are excitable cells?

A

cells that are capable of generating action potentials on stimulation

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2
Q

What are the two types of excitable cells?

A

neurons

muscle cells

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3
Q

What is an action potential?

A

short lasting event when the electrical membrane potential of a cell rapidly rises and falls

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4
Q

What is membrane potential?

A

difference in voltage between the interior and exterior of a cell

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5
Q

What is resting membrane potential?

A

when there is no net flow of the ion

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6
Q

What two components make up the electrochemical gradient?

A

voltage gradient

concentration gradient

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7
Q

How is the electrochemical equilibrium calculated?

A

NERNST equation

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8
Q

What is the NERNST equation?

A

E = RT/zF ln ([ion]o/[ion]i)

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9
Q

What is E in the NERNST equation?

A

equilibrium potential

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10
Q

What is R in the NERNST equation?

A

gas constant (2 cal mol-1 K-1)

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11
Q

What is T in the NERNST equation?

A

absolute temperature (K)

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12
Q

What is z in the NERNST equation?

A

valence (charge) of the ion

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13
Q

What is F in the NERNST equation?

A

Faraday’s constant (2.3 x 10^4 cal V-1 mol-1)

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14
Q

What is the equilibrium potential?

A

membrane potential at which there is no net flow of the ion

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15
Q

What is depolarization?

A

makes the membrane potential (cell interior) less negative

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16
Q

What is hyperpolarization?

A

makes the membrane potential (cell interior) more negative

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17
Q

What is inward current?

A

flow of positive charges into the cell

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18
Q

How does inward current impact the membrane potential?

A

depolarizes the membrane potential

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19
Q

What is outward current?

A

flow of positive charges out of the cell

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20
Q

How does outward current impact the membrane potential?

A

hyperpolarizes the membrane potential

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21
Q

What is an action potential?

A

property of excitable cells that consists of rapid

depolarization followed by repolarization of the membrane

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22
Q

What is the threshold?

A

membrane potential at which the action potential

is inevitable

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23
Q

What is the Resting Membrane Potential of a nerve?

A

~ -70mV

24
Q

At rest, are the Na+ channels opened or closed?

A

closed

25
Q

At rest, what is the level of K+ conductance?

A

high

26
Q

What are the three phases of an action potential?

A

depolarization (upstroke)
repolarization
hyperpolarization (undershoot)

27
Q

What are the steps in the upstroke/depolarization phase of an action potential?

A
  • stimulation
  • inward current depolarizes membrane current to threshold
  • depolarization causes opening of Na+ channels
28
Q

What are the steps in the repolarization phase of an action potential?

A
  • depolarization closes Na+ channel (more slowly than activated)
  • Na+ conductance returns toward zero
  • depolarization slowly opens K+ channels and increases K+ conductance to higher levels than at rest
  • combined effect of closing Na+ channels and opening K+ channels contribute to repolarization
  • outward K+ movement
29
Q

What are the steps in the hyperpolarization phase of an action potential?

A
  • K+ channel conductance remains higher than at rest

- makes it approach the K+ equilibrium potential

30
Q

The molecular events that initiate repolarization of the neuron can most accurately be described by which of the following:

  • Opening of a voltage activated calcium channel
  • Closing of the voltage activated Na+ channel and opening of a voltage activated K+ channel
  • Prolong refractory period
  • Inward movement of K+
A

Closing of the voltage activated Na+ channel and opening of a voltage activated K+ channel

31
Q

What is an absolute refractory period?

A

period in which another action potential cannot be elicited no matter how large the stimulus

32
Q

What is the relationship between the refractory period and the refractory period?

A

Coincides with the entire duration of the action potential

33
Q

What is the explanation for the absolute refractory period?

A

Activation gates of Na+ channels close when the membrane potential is depolarized, and remain closed until repolarization has occurred and gates have reset.

34
Q

What is a relative refractory period?

A

begins at the end of the absolute refractory period and continues until the membrane potential returns to resting levels

35
Q

In what context can an action potential be elicited during the relative refractory period?

A

if a stronger stimulus is provided

36
Q

What is the explanation for the relative refractory period?

A

K+ conductance is higher than at rest and the membrane potential is closer to the K+ equilibrium and further from the threshold

37
Q

What is the accommodation refractory period?

A

when the cell membrane is held at a depolarized level so the threshold potential is passed without firing an action potential

38
Q

What is a clinical example of the accommodation refractory period?

A
  • Hyperkalemia (high serum K+ levels)
  • causes depolarization of skeletal muscle membrane
  • although membrane potential is closer to threshold, action potentials do not occur because inactivation gates of Na+ channels are closed by depolarization
  • leads to muscle weakness
39
Q

Which ion’s equilibrium potential is a nerve’s resting potential closest to?

A

potassium equilibrium potential

40
Q

Which ion contributes most predominantly to the

upstroke? Does it move in or out of the cell?

A

sodium, in

41
Q

What two events contribute to the repolarization phase?

A

Na+ channels close

K+ channels open

42
Q

What is propagation of an action potential?

A

every next part of the membrane being sequentially depolarized

43
Q

If you measure membrane potential at several different points along an axon after an AP has fired, how will it look at each point?

A

identical

44
Q

What is a subthreshold stimulus?

A

stimulus that is too small in magnitude to produce an action potential in excitable cells

45
Q

How are subthreshold stimuli carried down an axon?

A

electrotonically conducted

46
Q

What is electrotonically conduction?

A

passive flow of a change in electric potential along a nerve or muscle membrane

47
Q

If you measure membrane potential at several different points along an axon after an subthreshold stimulus has fired, how will it look at each point?

A

the amplitude of the stimulus decays with distance as it moves away from the stimulus site

48
Q

What is conduction velocity?

A

the rate of the action potential conduction along a neuron limits the flow of information from the nervous system

49
Q

How does increasing the diameter of an axon impact the internal resistance?

A

decreases

50
Q

How does decreasing the diameter of an axon impact the internal resistance?

A

increases

51
Q

What is the relationship between the diameter of an axon and the internal resistance?

A

inverse

52
Q

What is Saltatory conduction?

A

action potential jumps from one node to the next

53
Q

What is the relationship between conduction velocity and axon diameter?

A

direct

54
Q

What is the relationship between conduction velocity and myelination?

A

exponential

55
Q

What neurotransmitter is present at a neuromuscular junction?

A

acetylcholine

56
Q

What are the steps for transmitting a signal at a neuromuscular junction?

A
  • nerve impulse arrives at axon terminal of motor neuron
  • triggers release of acetylcholine (ACh)
  • ACh diffuses, binds to its receptors
  • triggers muscle action potential
  • Acetylcholinesterase destroys ACh so more action potentials don’t arise
  • AP traveling along t tubule opens Ca2+ (calcium ion) channels in the SR
  • calcium enters into sarcoplasm
  • Ca2+ binds to troponin
  • Contraction
  • Ca2+ channels close and calcium transport pumps use ATP to restore low levels of calcium in sarcoplasm
  • Troponin complex returns to original position to block myosin binding sites on actin
  • Muscle Relaxes

Exam 1 (8 decks)

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