Potentials

Question 1

What direction would K and Na go if through simple diffusion?

Answer 1

Na would go into the cell and K would go out.

Question 2

How does the Na/K pump contribute to negativity intracellularly?

Answer 2

Inside the cell has a lot of negatively charged molecules which attract positive ions into the cell (causing swelling). When it starts getting too positive, 3Na go out of the cell and 2K come in the cell (against their [gradients] getting rid of +1 from inside.

1. Makes inside more negative
2. Water follows net +1 out of cell (solute)

Question 3

Why is the membrane potential negative?

Answer 3

If membrane were only permeable to K= -94
only permeable to Na=+61
But membrane is much more permeable to K so resting membrane potential is closer to its nernst potential

Question 4

What effect does changing permeability of Na and K have on membrane potential?

Answer 4

More permeable to K= closer to -94

More permeable to Na=closer to +61

Question 5

Describe the state of the Na and K gates during an AP.

Answer 5

Resting- Na inactivation gate open, activation gate closed. K activation gate closed.
Depolarization- Na both open for Na influx. K still closed.
Repolarization- Na inactivation gate open, activation gate closed. K activation gate finally opens so efflux of K.
Delay closure of K=hyperpolarization

Question 6

What is the role of the Na/K pump in APs?

Answer 6

They help bring the membrane potential negative by pumping Na out of the cell and K into the cell to get ready for the next AP.

Question 7

What are some general properties about APs?

Answer 7

All or none, constant amplitude- change in frequency encodes information, propagates in both directions

Question 8

How can an AP have a faster conduction velocity?

Answer 8

Larger fiber, myelination

Question 9

What limits the maximum frequency of Na channels?

Answer 9

Absolute refractory periods due to the inactivation of Na channels.

Question 10

What is saltatory conduction?

Answer 10

APs only occur at nodes of ranvier= increased velocity and energy conservation

Question 11

How is an SA node AP different than the classic AP?

Answer 11

Slow depolarization is due to inward Na current but then rapid depolarization is due to Ca current, then repolarization is outward K current.

Question 12

How does parasympathetic innervation affect it? What ion does it use? Sympathetic and ion?

Answer 12

PNS= longer time to reach threshold, accomplished by increasing K permeability
SNS= shorter time to reach threshold, accomplished by increasing Na permeability