Membrane Potential Flashcards

1
Q

What is membrane excitability?

A

The ability of a cell to generate action potentials

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2
Q

What two things are required to generate a resting membrane potential?

A

Unequal distributions of the ions across the cell membrane

Open ion channels in the resting membrane of the cell

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3
Q

What ions are present in high concentrations in the ECF?

A

Na and Cl

Ca is higher relative to inside, but relatively small compared to the other two

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4
Q

What ions are present in high concentrations in the ICF?

A

K and proteins (generate the negative charge)

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5
Q

What are leak channels?

A

Selective channels that are open in the resting, unstimulated membrane of the cell

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6
Q

What is the principle of electroneutrality?

A

The total mEq for cations equals the total mEq for anions in the ICF and ECF

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7
Q

What force is responsible for initially generating a resting membrane potential?

A

The concentration gradient causes initial diffusion of K out of the cell, but is slowed as the interior acquires a more negative charge

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8
Q

Describe the movement of K ions when the membrane potential is at equilibrium

A

There is no net movement.

Diffusion out due to concentration gradient is balanced by movement into the cell do to electrical potential

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9
Q

What equation describes the equilibrium potential for one ion?

A

The Nernst equation

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10
Q

How is the equilibrium potential affected by changes in [K]?

A

If the change in [K] results in a larger difference across the membrane, then the equilibrium potential will become more negative

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11
Q

What equation describes the equilibrium potential for more than one ion?

A

Goldman-Hodgkin-Katz equation

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12
Q

When considering multiple ions, how does permeability affect membrane potential?

A

The equilibrium potential will more closely resemble the equilibrium potential of the ion that is more permeable

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13
Q

How is the K concentration gradient maintained in the case of glial cells?

A

Since its only permeable to K, the potential can be predicted by the Nernst equation

The quantity of K ions that have to move to establish the resting membrane potential does not significantly alter the original concentrations, so the gradient is maintained

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14
Q

How are Na and K concentration gradients maintained in the case of neurons?

A

Na-K ATPase

Only a small amount of ion is moved to establish potential

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15
Q

When chloride ions are passively permeable to the membrane, how does Cl affect resting membrane potential?

A

Chloride ions will develop a concentration gradient that is exactly equal and opposite to the electrical potential across the membrane

In this case, the Cl ions do not contribute tot he resting membrane potential

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16
Q

When chloride ions are actively transported across the membrane, how does does chloride affect the resting membrane potential?

A

When actively transported, the concentration gradient established for Cl will result in an equilibrium potential that is only a few mV different from the RMP.

Therefore no significant contribution

17
Q

Which change in ion concentration affects resting membrane potential more, Na or K, and why?

A

K because it is more permeable

18
Q

What are the results of changes in extracellular Na concentration?

A

Significant effects on action potential

Significant effect on tonicity (osmolarity) and hypotonicity can cause cerebral edema

19
Q

What is membrane surface charge screening?

A

The extracellular-facing surface of the cell membrane contains fixed, negative charges.

Divalent cations, including Ca, bind to these charges and neutralize them

20
Q

How do hypocalcemia and hypomagnesemia affect membrane potential?

A

The charge-neutralizing effect of these ions is lost, and the membrane potential becomes less negative

21
Q

Why is the CNS partially protected from acute changes in blood electrolyte concentrations?

A

The presence of the blood-brain and blood-CSF barriers