Lecture 2/3- membrane potentials & action potentials Flashcards

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1
Q

How is the direction of current flow described?

A

the direction of net movement of positive ions

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2
Q

What is the resting membrane potential?

A
  • The difference in voltage between the inside and outside of the cell as measured across the membrane
  • -70mv
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3
Q

At rest, what ion is the membrane impermeable to?

A

Na+ ions

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4
Q

at rest, how are different ions and non-diffusible molecules (eg proteins) distributed?

A
  • Extra cellular - high Na+ and Cl-
  • intracellular - high K+ and proteins (with negatively charged side chains)
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5
Q

How is the RMP established?

A
  • Na+K+ ATPase pump - sets up concentration gradients, pumps 3 Na+ out of cell and 2 K+ into cell as it hydrolyses ATP - just with this pump we already have a more (+) outside and (-) inside
  • K+ leak channels - At RMP there is an increase of permeability to K+ than Na+ - more leak channels, Leak channels pump K+ out of cell which increases (-) charge in inside
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6
Q

What is a graded potential?

A
  • changes in membrane potential
  • no threshold or refractory period
  • involves ligand/ mechanically gated ion channels
  • signaling over short distances
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7
Q

Give examples of a graded potential?

A
  • receptor potential (sensory receptors eg hair cells )
  • Pacemaker potentials (eg SA node in right atrium)
  • Synaptic potential
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8
Q

What is the Nernst equation used to calculate?

A
  • it is used to calculate the equilibrium potential for 1 ion
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9
Q

What is the Goldmann equation used to calculate?

A
  • it calculates the resting membrane potential, the permeabilities of the ions and the concentrations of the ions
  • eg for Na+, K+ and Cl-
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10
Q

Why is the Goldmann equation and not the Nernst equation used to calculate RMP?

A
  • this equation takes into account that not all ions are equally permeable to the membrane
  • at rest, membrane is most permeable to K+ but there is also a small significant permeability to Cl- and K+
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11
Q

What is the equilibrium potential?

A
  • the electrical potential that can balance the concentration difference across the membrane
  • electrochemical equilibrium - conc of ion is evenly distributed
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12
Q

What is depolarisation?

A
  • potential becomes less negative (more Na+ in cell)
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13
Q

What is repolarisation?

A
  • When MP has been depolarised and it goes back to resting value - more (-) again
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14
Q

What is hyperpolarisation?

A
  • When the potential is more (-) than the resting value
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15
Q

What is an action potential?

A
  • large difference in membrane potential
  • large depolarisation
  • involves voltage gated ion channels eg Na+, K+ Ca2+ etc
  • signaling over long distances
  • only occurs in excitable cells eg neurons and muscles
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16
Q

Describe the steps of the initiation of an AP

A
  1. RMP close to K+ equilibrium (leak channels)
  2. AP begins with depolarising stimulus (eg neurotransmitter binding to receptor)
  3. Depol causes voltage gated Na+ channels to open and causes influx of Na+ into cell
  4. further depol leads to threshold
  5. this opens all VG Na+ channels- rapid depol
  6. Rapid Depol overshoots @ peak value ( v +)
  7. K+ channels are slow to close - this causes influx of K+ out of cell - repolarisation
  8. Closing of K+ channels returns the MP to RMP
17
Q

Compare voltage gated Na+ and K+ channels.

A
  • Na+ -rapid opening and inactivation, responds faster to changes in MP
  • K+- opens and closes in response to changes in MP very slowly (delayed response)
18
Q

What is the relative refractory period?

A
  • interval where 2nd AP can be generated only if stimulus is strong enough (after hyperpol)