Excitable Cells Part 2 (6/19/15) Flashcards Preview

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Flashcards in Excitable Cells Part 2 (6/19/15) Deck (40)
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1
Q

Describe the 6 steps of establishing a resting membrane potential….

A
  1. There is a concentration gradient across the plasma membrane for K+.
  2. Permeability for K+ is greater so K can leave the cell (more K inside the cell to begin with)
  3. K+ ions move down concretion gradient leading to the development is a diffusion potential.
  4. Equilibrium is reached when the force in the concentration gradient for K+ ions is balanced out by the opposing force in electrical gradient which favors keeping the K+ ions IN the cell.
  5. At this point, membrane potential is very close to the equilibrium potential for K+. Resting membrane potential does not = Equilibrium potential for K+ because Na+ still affects it some. (Na is diffusing into the cell down both its concentration and electrical gradient, keeping the resting membrane potential slightly lower than EK.)
  6. Therefore, K+ ions diffuse out of the cell and Na+ ions diffuse into the cell at rest!
2
Q

True for False, Resting membrane potential is not steady.

A

False, it is! It is not a transient diffusion potential.

3
Q

What does the Na/K pump do?

A

Uses ATP energy to pump K+ ions back into the cell and Na+ out of the cell, when the cells are at rest.

4
Q

What happens if the Na/K pump gets poisoned?

A

A slow decrease in the resting membrane potential (moves toward 0 mV)

5
Q

_______ moves toward 0 mV.

A

Depolarization (Rising phase)

6
Q

_______ moves toward resting potential.

A

Repolarization (Falling phase)

7
Q

_______ increase in membrane potential.

A

Hyperpolarization

8
Q

______ is a membrane portion found within almost all cells.

A

Na/K pump

9
Q

Na/K pump is an example of _____.

A

Homeostasis

10
Q

What is an Action Potential?

A

A large transient change in membrane potential (Neurons and muscle cells)

11
Q

Where is the Action potential initiated?

A

in the Initial segment of the neuron (never in cell body or dendrite)

12
Q

What are the steps to CREATING an action potential?

A

Stimulus –> depolarizes membrane (dendites of neuron) –> Depolarizes cell body –> AP first develops at initial segment –> action potential propagates down axon.

13
Q

What are the steps DURING the development and Time course of an Action potential?

A
  1. Increase in membrane permeability to Na+ ions.
  2. Na+ ions enter through Na channels driven by the concentration and electrical gradient, carrying + charges with them. *These Na channels are voltage regulated!
  3. The membrane potential move closer to 0 mV (rising phase/depolarization)
  4. If depolarization is sufficient, threshold point will be reached and many more Na channels will open and more Na+ enters the cell!
  5. Now the membrane potential move VERY RAPIDLY toward 0 mV and overshoots, reaching a peak @ around +40 mV.
  6. K channels open (increasing K+ permeability) because they too are voltage aged and K+ ions cross over to outside of cell.
  7. Membrane potential abruptly reverses direction and rapidly returns to resting value as K+ ions diffuse out of the cell. *When 0 mV is hit during the falling phase the electrical gradient will be lost for K+ which will inhibit K+ moving out of the cell. In other words, K+ will move out of cell via electrical gradient as long as potential is +).
  8. Overshoots Hyperpolarization
14
Q

T or F, a relatively small number of ions can result in a large change in membrane potential.

A

True!

15
Q

What is the latent period?

A

A very brief period between applying a stimulus and beginning of depolarization during the rising phase of an AP.

16
Q

The latent period precedes the ________.

A

Foot of the AP which is the portion of the rising phase before the threshold is reached.

17
Q

Why does the peak of the AP stop at approx. 40 mV?

A

B/C peak of AP is approaching Eq of NA (58 mV) which it cannot reach unless K+ channels do not open.

18
Q

What is the relationship between the concentration gradient and electrical gradient of Na+ at peak of AP?

A

The electrical and Concentration gradients are nearly equal at Peak AP.

19
Q

The End of the repolarization phase (The resting membrane potential) is close to _______.

A
equilibrium K (eK)
*B/C permeability of K is very high during the falling phase of AP until the concentration and electrical gradient are nearly balanced at  end of AP.
20
Q

________ is insufficient to take membrane to threshold.

A

Sub-threshold stimuli

21
Q

________ is just sufficient to take membrane to threshold.

A

Threshold stimulus

22
Q

________ is Greater than a threshold stimulus.

A

Supra-threshold stimulus

23
Q

Events resulting from a sub threshold stimuli is confined to where?

A

The immediate region of the membrane

24
Q

________ are small depolarizations or hyper-polarizations that do not move along the membrane.

A

Local responses

25
Q

_____ responses are proportional to stimulus strength.

A

Graded responses

26
Q

What happens if threshold is reached?

A

An AP WILL occur, it is automatic at that point.

27
Q

What is an Absolute refractory period?

A

Brief period when a second threshold stimulus cannot elicit a second AP.

28
Q

What is a Relative Refractory period?

A

For a longer period after and AP a supra-threshold can elicit another AP, but a threshold stimulus cannot.
*Basically it imposes an upper limit on the frequency at which cells can fire AP’s. This is important in the heart.

29
Q

_______ binds to Na channels and blocks sodium influx.

A

Tetrodotoxin (TTX) from pufferfish

30
Q

What is the stimulus strength-duration curve?

A

Curve that relates strength of an instantaneous stimulus to the duration of that same stimulus that is required to elicit a response.

31
Q

A Drug that enhances stimulus sensitivity would shift the stiumuls strength-duration curve to the _______.

A

Left!

32
Q

A Drug that enhances stimulus sensitivity would shift the stimulus strength-duration curve to the ______.

A

Right!

33
Q

What is Rheobase?

A

The magnitude of least intense stimulus that can elicit a response.

34
Q

What is Utilization time?

A

duration required to elicit response by a stimulus with a Rheobase magnitude.

35
Q

What is Chronaxie?

A

duration required to elicit a response by a stimulus TWICE the strength the magnitude of the Rheobase stimulus *used to compare the excitability of different cells.

36
Q

_____ are passive currents (do not propagate) that occur at immediate site of stimulation.

A

Local currents

37
Q

T or F, AP’s only go in one direction.

A

True, due to Na+ channel inactivation.

38
Q

_____ wrap extensive layers of plasma membrane around axon except at periodic nodes (nodes of ranvier)

A

Schwann cells

39
Q

Action potential in a nerve bundle is known as _______.

A

Compound action potential

40
Q

Axons with larger diameters have ______ velocities.

A

Higher velocities