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FHB Exam 1 - Cardiovascular Physiology > Lecture 1 - Neuronal Action Potential > Flashcards

Lecture 1 - Neuronal Action Potential Flashcards

1
Q

Which vertebrate cell has the longest duration?

  1. Motor
  2. Skeletal
  3. Cardiac Ventricle
A

Cardiac ventricle

  • duration is fast, about 200 milliseconds
  • heart has long AP to protect it from additional AP’
  • thus cannot be activated as quickly
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2
Q

What is the term for the response that does NOT generate an AP because the voltage is not large enough?

A

Sub threshold response

  • decreases in amplitude with distance
  • change in membrane potential not sufficient for action potential
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3
Q

What is the length constant?

A

Distance over which a sub threshold depolarization (local response) will spread & influence the next membrane

  • larger length constant = MORE RAPID CONDUCTION
    (fires an AP)
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4
Q

When you decrease Rm, what happens to the space constant? What about decreasing Ri?

A
  1. decrease Rm = decrease length constant

2. decrease Ri = INCREASE length constant

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5
Q

What is Rm and Ri?

A 
Rm = membrane resistance
Ri = internal resistance (or Ra)
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6
Q

With a large axonal diameter, is the length constant large or small?

A

length constant is LARGE since Ri is LOW(internal resistance)

-

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7
Q

As distance increases from the current source, what happens to the sub threshold voltage?What manner does this decay (graph wise)

A

DECREASES (decays) with increasing distance from source

  • decays EXPONENTIALLY
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8
Q

Larger diameter axons have lower or higher membrane and internal resistance? (rm and Ri)

A

Large diamter = LOWER resistance than smaller axon

  • but since Ri is squared, it decreases more than rm
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9
Q

Large diameter results in _____ conduction

A

Faster conduction velocity

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10
Q

What determines how easily an axon can conduct an AP?

A

Space constant

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11
Q

What determines the space constant?

A

membrane Resistance

internal Resistance

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12
Q

What occurs once an area of membrane is activated by an action potential?

A

REVERSAL OF MEMMBRANE POLARITY

inside becomes more positive than outside
- originally NEG inside

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13
Q

Local current flow occurs between activated (depolarized) and inactive regions, activating ______ channels to depolarize the next segment of membrane and initiating an AP/

A

NA channels!!!

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14
Q

A stimulus is a ____ or ____ response.

A

All or none

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15
Q

Upstroke of the action potential graph is caused by what? Repolarization is caused by what?

A
  1. Na activation (opening of M channels)

2. delayed increase in K+ conductance and inactivation of Na channels (closing of h gates)

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16
Q

Where is the only place AP’s occur?

A

Nodes of Ranvier

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17
Q

An action potential occurs between the E of what two ions?

A

Ena and Ek

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18
Q

Repolarization turns off what channel conductance completely?

A

K+ (deactivated)

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19
Q

Describe the gating properties of Na channel at the following stages:

  1. Resting
  2. Activated
  3. Inactivated
A
  1. resting: M closed, h open
  2. Activated: both open, NA INFLUX (h slowly closing)
  3. Inactivated: M open, h closed
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20
Q

What is the time required to reset the channel from inactivated state back to resting state?

A

Recovery from Inactivation

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21
Q

Recovery from inactivation requires what?

A

Repolarization

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22
Q

Gating kinetics for Na and K both depend on what?

A

Time and Voltage

23
Q

What gates due NOT have inactivation gates?

A

K+

24
Q

What channels respond RAPIDLY to depolarization?

A

Na+ channels

25
Q

What occurs during regenerative depolarization?

A
  1. Na+ moves into the cell down its electrical & conc gradient
  2. DEPOLARIZE membrane to Ena
  3. increase Na permeability
  4. causing FURTHER DEPOLARIZATION
26
Q

What channels close rapidly at depolarized (positive) voltages?

A

Na+

  • inactivation is time and voltage dependent
27
Q

What is the basis for refractory periods?

A

Voltage-dependent inactivation of Na+ channels

28
Q

Recovery from inactivation requires what?(to reach resting state)

A
  1. time

2. Negative voltages (repolarization)

29
Q

What channels remain open with maintained depolarization of the membrane? When do these channels completely deactivate?

A

K+!!!

  • no inactivation
  • completely deactivate with DEPOLARIZATION
30
Q

What flows into the cell, what flows out?

A

NA in, K+ out (down its conc gradient)

Na moves down its electric and chemical gradient

31
Q

Depolarization of the membrane potential toward Ek causes the potential to go more negative than RMP, called:

A

HYPERPOLARIZATION

32
Q

What is the time during which a stimulus CANNOT elicit a regenerative response? When does this occur?

A

ABSOLUTE refractory period

  • occur during Na+ inactivation during depolarization and increase in membrane potential to more positive values
33
Q

What is the time during which a stimulus CAN elicit a regenerative response/AP? When does this occur?

A
  1. Relative Refractory Period
  2. when membrane potential RE-polarizes, Na+ channels recover from inactivation and reach RESTING state

HYPERPOLARIZATION

34
Q

As the voltage becomes more positive, the number of Na channels/conductance increases or decreases?

A

Decreases!
- at -60mV 50% of sodium channels open

BUT
at -90 –> 100% are open

35
Q

Conduction can be slowed causing muscle weakness. This would be due to loss of what channels?

A

Sodium channels

36
Q

Refractory periods in nerve (and heart) are solely based on voltage-depends characteristic of what channels?Which specific gate?

A
  1. SODIUM!
  2. H gate!!!
  • inactivated at positive voltages

re-polarization = Na+ channels recover

37
Q

What cation modulates Sodium channel activity?

A

CALCIUM!

38
Q

If membrane bound calcium increases, what happens to sodium channels?

A

BECOME INACTIVATED

  • believe that area has become more positive
  • H gates CLOSE!
39
Q

What occurs to the following during HYPERCALCEMIA:

  1. calcium concentration
  2. Na+ threshold
  3. Membrane excitability
A
  1. increases
  2. increases
  3. decreases membrane excitability
40
Q

How can hypercalcemia be tested clinically?

A

REFLEX TEST

  • slower/muted reflexes are a sign
41
Q

How can hypocalcemia be tested clinically?

A

REFLEXES

  • hyper-reflexivity is a result of increased membrane excitability due to low calcium conc.
42
Q

What occurs to the following during HYPOCALCEMIA:

  1. calcium concentration
  2. Na+ threshold
  3. Membrane excitability
A
  1. decreases
  2. decreases
  3. INCREASES membrane excitability
43
Q

What occurs to the following during Hyperventilation:

  1. CO2 concentration
  2. respiratory state
  3. Membrane excitability

What is a sign?

A
  1. decreased CO2
  2. Respiratory Alkalosis
  3. Increased membrane excitability

(irritable)

44
Q

What occurs to the following during Hypoventilation:

  1. CO2 concentration
  2. respiratory state
  3. Membrane excitability

What is often the cause?

A
  1. more CO2
  2. Respiratory acidosis (co2 binds to water to make acid)
  3. decreased membrane excitability
    ex: barbituates, foreign object in trachea
45
Q

What occurs during Hyperkalemia to the following:

  1. RMP
  2. Na+ channels
  3. inward Na+ current & conduction
  4. SIGNS & SYMPTOMS
A
  1. more positive resting membrane potential

(increase K+)

  1. Na+ channels inactivated
  2. inward Na+ DECREASED = slower conduction
  3. Slow mentation, muscle weakness
46
Q

What is the normal serum potassium level?

A

3-5mmol

  • higher = hyperkalemia
47
Q

Potassium levels often change with what diseases?

A

Renal Failure

  • Hyperkalemia occurs
48
Q

What allows us to have significantly greater conduction velocity?

A

Myelination of axons

49
Q

What increases conduction more, myelination or axon diameter?

A

MYELINATION

  • unmyelinatd axons 100 times greater in diameter
50
Q

What is the only place not covered by Schwann cells?

A

Node of Ranvier

51
Q

Myeline sheath increases what? This increases or decreases the length constant and conduction velocity?

A

Rm

  • increases length constant
  • increases conduction velocity
52
Q

What is internal distance between 2 nodes of Ranvier?

A

1-2 mm

53
Q

Na+ channels are concentrated where? What is found here? This type of conduction is called:

A
  1. Nodes of Ranvier
  2. Action POtentials
  3. SALTATORY CONDUCTION
54
Q

What diseases destroy myelination and slow neuronal conduction?

A

Diabetic neuropathies

Multiple Sclerosis

FHB Exam 1 - Cardiovascular Physiology (26 decks)

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