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Physiology 6600 > Excitable cells > Flashcards

Excitable cells Flashcards

1
Q

What can electrical events do in cells?

A
  1. Cell to cell communication
  2. Sensing environmental changes
  3. Triggering intracellular events
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2
Q

Extracellular fluid has a high concentration of what?

A

NaCl

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3
Q

What is the most dominant salt in the intracellular fluid?

A

KCl

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4
Q

What are some examples of non-polar substances?

A

O2
CO2
Fatty acids
Steroid hormones

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5
Q

What is flux in diffusion?

A

The amount of a substance crossing a surface per unit time

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6
Q

T/F diffusion between two compartments is always unidirectional?

A

False- it is always bi-directional

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7
Q

What is net flux in diffusion?

A

It is the difference between the two unidirectional fluxes

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8
Q

Define diffusion equilibrium.

A

Net flux=0

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9
Q

T/F there is more sodium on the outside of the cell and more potassium on the inside than the outside of the cell?

A

True!

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10
Q

Does facilitated diffusion require energy?

A

Nope

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11
Q

How does facilitated diffusion work?

A

A membrane protein serves as a carrrier to translocate a molecule across the membrane

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12
Q

What is active transport?

A

It requires energy because a transporter helps a molecule move against a concentration gradient- the transporters are referred to as pumps

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13
Q

In mediated transport, what is the general model? How is activate transport different?

A

A solute binds to the transporter protein. A conformation change occurs. The transporter protein closes on one side and opens on the other to allow the solute free passage.
Active transport is different because the molecule is moving against the concentration gradient. Energy is required to do this- generally ATP- which phosphorylates the transporter, allowing active transport to occur

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14
Q

What are two examples of primary active transport?

A

Transport Na+ ions out of cells

Transport K+ ions into cells

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15
Q

How does the secondary active transport model work?

A

This model uses the energy in the concentration gradient across the membrane instead of ATP. This is the main difference between secondary and primary active transport.

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16
Q

What three factors determine the rate of flux?

A
  1. The number of transporters in the membrane
  2. Extent of transporter saturation (this is affected by transporter affinity and ligand concentration)
  3. Rate of transporter conformational change
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17
Q

What types of channels are there? (3)

A

Ligand sensitive
Voltage sensitive
Mechanosensitive

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18
Q

Water diffuses through what?

A

Aquaporins

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19
Q

What is the osmolarity of ECF?

A

300 mOsm

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20
Q

1 osmole = 1 mole of solute. 1 mole of NaCl is how many osmoles?

A

2

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21
Q

Know isotonic, hypo and hypertonic

A

deal.

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22
Q

What is the difference between isotonic and isoosmotic?

A

Isotonic considers non-penetrating molecules only.

Isoomotic considers both penetrating (can cross the membrane rapidly) and non penetrating (can’t cross the membrane)

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23
Q

Can a solution be hyper osmotic and isotonic at the same time? Why or why not?

A

Yep- because one refers to penetrating and non-penetrating whereas one refers to non-penetrating only.

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24
Q

What is the difference between pinocytosis and phagocytosis?

A

Pinocytosis- engulfing small particles with or without ECF, performed by all cells

Phagocytosis- engulfing large particles, performed by phagocytes exclusively

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25
Q

During endocytosis, part of the cell membrane makes up the vesicle. How is that remedied?

A

During exocytosis, the vesicle expels its contents outside the cell and replaces the cell membrane portion that was taken away by endocytosis

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26
Q

The charge difference between the inside and outside of the cell is called….?

A

Voltage

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27
Q

The plasma membrane must have a resistance. When resistance changes, ions cross the membrane and the ion movement is current.

A

Perfect

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28
Q

T/F conductance and resistance are both membrane properties?

A

True

29
Q

Know how to use the Nernst equation.

A

It’s on the test

30
Q

Why do transient diffusion potentials exist?

A

Well, some ions can more more easily or quickly through the membrane than others, thereby creating a diffusion potential that is transient

31
Q

How does a steady diffusion potential exist?

A

If a membrane becomes permeable to just one ion, it will follow its concentration gradient until the concentration gradient and the voltage gradient kind of balance each other out.

32
Q

What is resting membrane potential?

A

There is a higher concentration of K+ inside the cell and a higher concentration of Na+ outside the cell- this results in a potential difference

33
Q

In active transport, energy is required. What can that energy affect?

A

The affinity of the transporter for the ligand

The rate of conformation change of the transporter

34
Q

A sodium/potassium pump active transport system is what an example of what kind of active transport?

A

Primary active transport.

35
Q

Where do the primary and secondary active transport models get their energy from?

A

Primary active transport gets its energy from the hydrolysis of ATP
Secondary active transport gets its energy from the ion concentration gradient across the membrane

36
Q

What are the three steps in mediated transport?

A
  1. Ligand binds to transporter
  2. Transporter undergoes conformational change
  3. Ligand is released on the other side of the membrane
37
Q

At rest, what are cell membranes primarily permeable to? What does this mean?

A

Potassium (K+)

A diffusion potential results

38
Q

What are two factors that affect diffusion and equilibrium?

A

Concentration gradient for the permeable ion and the voltage difference- there comes a point where the electrical gradient effectively halts continued diffusion of a certain ion down its concentration gradient

39
Q

At rest, K+ ions flow ____ the cell and Na+ ions diffuse _____ the cell. Why?

A

out of the cell
into the cell
Because they’re following their concentration gradients

40
Q

What maintains the membrane potential?

A

The sodium/potassium pump

41
Q

What is depolarization?

A

It is a movement of the voltage potential toward 0

42
Q

What is repolarization?

A

movement towards the resting potential- IE becoming more negative again

43
Q

What is hyper polarization?

A

An increase in the membrane potential- becoming more negative

44
Q

The Na+/K+-ATPase pump does what?

A

Transports K+ in and Na+ out

45
Q

Why is the Na+/K+-ATPase pump important?

A

without it, the resting membrane potential would slowly dissipate to 0 mV.

46
Q

T/F the Na+/K+-ATPase pump is an example of homeostasis?

A

True

47
Q

What is an action potential?

A

It is a large transient change in membrane potential

48
Q

Where is an action potential initiated on a neuron?

A

At the initial segment

49
Q

After an action potential, what happens to the membrane potential?

A

It briefly hyper polarizes before it returns to the resting negative membrane potential of about -70mV

50
Q

There are 9 steps for an action potential from start to finish. What are they?

A
  1. There is an increase in membrane permeability to Na+ ions
  2. Na+ ions enter the cell, driven by electrical and concentration gradients- pass through voltage-regulated Na channels.
  3. This is depolarization- membrane potential moves closer to 0
  4. If depolarization is sufficiently large, a threshold is reached at which point additional Na channels open (more voltage regulated channels)
  5. More Na+ enters the cell and conduction increases more (this is the rising phase)
  6. Very rapidly, the membrane potential moves towards 0 and then past it to about +40 mV.
  7. At this point, K channels open because they too are voltage gated
  8. K+ ions leave the cell and repolarization starts- this is the start of the falling phase. The movement of K+ is driven by both a concentration gradient and the electrical gradient. Na channels close during this phase as well
  9. Overshoot occurs where hyper polarization occurs and the membrane potential goes past the membrane potential just a little bit
51
Q

In an action potential, what is the latent period?

A

It is a very brief period between applying a stimulus and the beginning of depolarization

52
Q

Where is the latent period found on a graph of the action potential?

A

It is found at the very beginning- the part right before the really steep slope

53
Q

Events resulting from a sub threshold stimulus are confined to where?

A

The immediate region of the membrane where it takes place

54
Q

What are local responses?

A

They are small depolarizations or hyperpolarizations that do not move along the membrane- they’re graded responses that are proportional to the stimulus strength

55
Q

If threshold is reached, an action potential occurs- it’s automatic

A

It’s kind of an all or none property

56
Q

What is the absolute refractory period?

A

It is a brief period where it is impossible for a second threshold stimulus or even a supra threshold stimulus cannot elicit a second action potential

57
Q

What is a relative refractory period?

A

This is a time period after an AP where a threshold stimulus won’t elicit another action potential but a supra threshold stimulus will

58
Q

In nerve cells, what is accommodation?

A

Its an adaptive property of nerve cells, due to a property of the channels- if you were to quickly apply a 10mV stimulus, an action potential would result. If you apply that same 10mV stimulus but in a ramp like manner (slowly) then no action potential results

59
Q

What is a rheobase?

A

It is the magnitude of the least intense stimulus that can elicit a response

60
Q

What is utilization time?

A

It is the duration required to elicit a response by a stimulus with a rheobase magnitude

61
Q

What is chronaxie?

A

It is the duration required to elicit a response for a stimulus that has a magnitude that is twice the rheobase magnitude- it can be used to compare the excitability of different cells

62
Q

T/F, AP’s occur along the entire length of the axon?

A

True

63
Q

What are electronic or local currents and what do they do?

A

They occur at the immediate site of stimulation, but the don’t propagate- they’re passive currents. However, if they’re large enough, they will cause an AP

64
Q

Cathode causes cations to move toward it

A

Remember that!

65
Q

Anode attracts anions

A

Remember this!

66
Q

T/F the mechanism of AP propagation is bidirectional?

A

False- it is in one direction!

67
Q

T/F- Local currents can go in both directions but action potentials can only proceed in one direction

A

Fact.

68
Q

Why do AP’s only proceed in one direction?

A

This is due to sodium channel inactivation

69
Q

Saltatory conduction is what?

A

Myelinated cells allow for AP’s to only be generated at the nodes between schwann cells- this greatly increases the speed with which AP’s are propagated

Physiology 6600 (10 decks)

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