Membrane Physiology Flashcards

1
Q

Describe the relative compositions of K+, Na+, Ca2+ and Cl- outside and inside the axon phospholipid bilayer.

A
  • High K+ inside.
  • High Na+ outside.
  • High Ca2+ outside.
  • High Cl- outside.
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2
Q

What maintains the ionic gradients over an axon’s phospholipid bilayer?

A

Ion pumps.

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3
Q

What is the membrane potential (Em) of most neurones?

What does this mean?

A

~-65mV.

  • This means there is a relative excess of negative charge inside.
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4
Q

What is the function of leak channels on neuronal membranes?

A

To set the membrane potential by allowing passive movement of ions across the membrane.

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5
Q

What is the function of voltage gated channels on neuronal membranes?

A

To generate action potentials.

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6
Q

What is the function of ligand gated channels on neuronal membranes?

A

To generate membrane potential changes.

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7
Q

What determines a membrane’s permeability to particular ions?

A

The number of channels for that ion present on the membrane.

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8
Q

What two factors influence the movement of ions across a membrane?

How do these factors influence movement of ions across neuronal membrane specifically?

A
  • Electrical and chemical.
  • In a neurone, [K+] is higher inside so drive for K+ efflux.
  • In a neurone, [Na+] is higher outside so drive for Na+ influx.
  • At a negative membrane potential, there is a drive for both K+ and Na+ to move in.
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9
Q

What is the equilibrium potential for K+?

Describe how this would be set up in the hypothetical situation where the membrane is only permeable to K+.

A
  • EK = -80mV.
  • Initially, Em is 0 and [K+] is greater inside, so K+ efflux occurs.
  • This causes Em to become more negative.
  • Negative Em creates electrical force causing K+ influx.
  • When Em is negative enough (-80mV), influx = efflux.
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10
Q

What is the equilibrium potential for Na+?

Describe how this would be set up in the hypothetical situation where the membrane is only permeable to Na+.

A
  • ENa = +62mV
  • Initially, Em is 0 and [Na+] is greater outside, so Na+ influx occurs.
  • This causes Em to become more positive.
  • Positive Em creates electrical force causing Na+ efflux.
  • When Em is positive enough (+62mV), influx = efflux.
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11
Q

How do the chemical and electrical influences of Na+ and K+ across a membrane differ at resting membrane potential of -65mV?

What is the implication for the driving force of both ions?

A
  • K+ chemical influence is efflux as [K+] is higher inside, whereas its electrical influence at -65mV is influx.
  • Na+ chemical influence is influx as [Na+] is higher outside, and Na+ electrical influence at -65mV is also influx.
  • Implication is Na+ has a greater driving force for influx than K+ does for efflux.
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12
Q

Define equilibrium potential.

A

The voltage at which an ion is in equilibrium (when chemical gradient and electrical force are in balance).

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13
Q

What does the value of membrane potential depend on?

A

The relative permeabilities of K+ and Na+.

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14
Q

Why is membrane potential closer to the equilibrium potential of K+ than Na+?

A

Because the permeability of potassium is 40x greater than that of sodium.

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