Exam #1: Action Potential Flashcards Preview

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Flashcards in Exam #1: Action Potential Deck (35)
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1
Q

What is the depolarization phase of an action potential? What ion is responsible for depolarization?

A

Portion of the Na+ channels are activated, resulting in the rising phase of the action potential (increase in membrane potential)

2
Q

What is the overshoot of an action potential? What ion is responsible for over shoot?

A

Activation of Na+ channels leads to depolarization above 0mV

3
Q

What is the repolarization phase of an action potential? What ion is responsible for repolarization?

A

Potassium channel activation leads to the efflux of K+ & decreased in membrane potential

4
Q

What is the undershoot of an action potential? What ion is responsible for undershoot?

A

Prolonged opening of K+ channels leads to a dip in membrane potential below resting membrane potential

5
Q

What is the hyperpolarization phase of an action potential? What ion is responsible for hyperpolarization?

A

Prolonged opening of K+ channels leads to a dip in membrane potential below resting membrane potential

6
Q

Draw an action potential. Label ion movement for each phase of the action potential.

A

N/A

7
Q

What happens to the conductance of Na+ & K+ in the action potential?

A
  • Pk > PNa at rest
  • PNa > Pk during depolarization
  • PNa > Pk at over shoot
  • PNa waning during repolarization
  • Pk > PNa during hyperpolarization/ undershoot
  • Pk > PNa at rest
8
Q

What are the three possible states for the rapidly inactivating Na+ channel?

A

Sodium channels are voltage-gated and have 2x gates, an activation gate & an inactivation gate. The two gates give rise to three states:

1) Resting= activation gate closed & inactivation gate open
2) Activated= both open
3) Inactivated= activation gate open & inactivation gate closed

9
Q

What is the absolute refractory period?

A

A second response is not possible regardless of strength or duration of the stimulus
- Na+ channel inactivation

10
Q

What is the relative refractory period?

A

A second response can be elicited but at a greater cost i.e. strength or duration
- K+ channel prolonged opening

11
Q

What factors control the speed of action potential conduction?

A

Size

12
Q

How does axon diameter relate to speed of action potential conduction?

A

Larger= faster

Directly proportional to length constant
Inversely proportional to time constant

13
Q

Where are voltage-gated Na+ channels located in myelinated & unmyelinated nerves?

A

Nodes of Ranvier

14
Q

Which conducts more rapidly, myelinated or unmyelinated nerves? Why?

A

Myelinated

  • Myelination greatly decreases axon membrane capacitance and increases membrane resistance
15
Q

Which conducts more efficiently, myelinated or unmyelinated nerves?

A

Myelinated

16
Q

What is saltatory conduction?

A

Jumping of current from node to node

17
Q

Which causes spontaneous muscle twitches, hypo or hypercalcemia?

A

Hypocalcemia

18
Q

What causes Trousseau’s sign?

A

Much more sensitive and specific sign of hypocalcemia than Chvostek’s sign
- BP cuff inflation leading to muscle spasm of arm & hand

19
Q

What causes Chvostek’s sign?

A

A possible sign of latent tetnay associated with hypocalcemia
- Contraction of muscles of the eye, mouth, nose elicited by tapping over facial nerve in front of ear

20
Q

What change can cause muscle weakness, fatigue, mental confusion, and coma?

A

Hypercalcemia

21
Q

What cell type is responsible for myelination in the CNS?

A

Oligodendrocytes

22
Q

What cell type is responsible for myelination in the PNS?

A

Schwann Cells

23
Q

What is Guillian-Barre Syndrome? What part of the nervous system is affected?

A

Demyelination of the PNS (Schwann cells)

  • Autoimmune disease
  • Can undergo remyelination
24
Q

What is Multiple Sclerosis? What part of the nervous system is affected by MS?

A

Demyelination of the CNS (oligodendrocytes & axons)

  • Autoimmune disease
  • Cannot undergo remyelination
25
Q

What is the time constant?

A

Amount of time it takes for the voltage to change by a certain percentage

26
Q

What is the time constant a function of?

A

Product of the axon’s electrical resistance (R) & capacitance (C)

27
Q

What is the length constant?

A

Distance between current injection site & point where that voltage has decayed 63%

28
Q

What two tissues types are considered excitable?

A

Nerve & muscle

29
Q

What is TTX?

A

Tetrodotoxin from the puffer fish, a Na+ channel blocker

30
Q

What is the mechanism of action of Lidocaine? What is Lidocaine used for?

A
  • Na+ channel antagonist

- Local anesthesia

31
Q

What is the definition of AP threshold?

A

Lowest voltage or minimal depolarization needed to drive Na+ channels into the fast, positive, feedback loop

32
Q

What factors influence AP threshold?

A

Na+ Channel
K+ Channel
Ca++ ECF

33
Q

What are the CATS of hypocalcemia?

A

Convulsions
Arrhythmia
Tetany
Stridor

34
Q

How does Ca++ change threshold?

A

External Ca++ influences AP threshold by changing Na+ open probability (% of channels that will open)

35
Q

Experimentally, if an axon is stimulated somewhere in the middle, which direction will current flow? Does this happen in life?

A
  • Both
  • No, the axon hillock has the lowest AP threshold
  • K+ channels in subsequent Nodes of Ranvier prevent backward direction of AP propagation

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