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BRS > Membrane Potentials and Action Potentials > Flashcards

Membrane Potentials and Action Potentials Flashcards

1
Q

what is voltage?

A

generated by ions to produce a charge gradient = potential difference

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2
Q

what is current?

A

movement of ions due to potential difference

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3
Q

what is resistance?

A

barrier that prevents the movement of ions

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4
Q

which three things can cause ion channels to open/close?

A
  • transmembrane voltage
  • mechanical force
  • binding of ligands
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5
Q

what is an electrochemical equilibrium?

A

when the concentration gradient exactly balances the electrical gradient ie. electric force= concentration force

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6
Q

what does the Nernst equation enable you to calculate?

A

electrochemical equilibrium potential

eg. potential at which the concentration of potassium moving out of the cell is exactly balanced by the electrical gradient that occurs as you move potassium out of the cell

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7
Q

what is the concentration of sodium extracellularly and intracellularly, respectively?

A

150mM and 10mM

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8
Q

what is the concentration of potassium extracellularly and intracellularly, respectively

A

5mM and 150mM

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9
Q

why is the resting potential -70mV and not -90mV?

A

some sodium can still enter the cell

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10
Q

what does the Goldman-Hodgkin_Katz (GHK) equation describe?

A

resting membrane potential

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11
Q

depolarisation meaning

A

membrane potential moves towards 0mV

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12
Q

repolarisation

A

membrane potential becomes more negative towards resting membrane potential

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13
Q

overshoot

A

membrane potential becomes more positive from 0

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14
Q

hyperpolarisation

A

when potential becomes more negative than resting potential

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15
Q

what happens to the charge as a small depolarisation propagates down an axon? What is this called?

A

charge leakage resulting in the depolarisation fading away - graded potentials

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16
Q

Where does a graded potential occur? What do they do in terms of action potentials? What are they in response to?

A
  • synapses and sensory receptors
  • initiate or prevent
  • stimulus
17
Q

where do action potentials occur?

A

exciteable cells - muscle, cardiac tissue, neurons (nerve impulse) and some endrocrine tissue

18
Q

what does membrane potential depend on

A

movement of potassium through CHANNELS not pumps

19
Q

what are the 5 phases of an action potential?

A
  1. resting potential
  2. depolarising stimulus
  3. upstroke
  4. repolarisation
  5. after - hyperpolarisation
20
Q

how is resting potential maintained?

A

K+ flow out of cell, small amount of Na+ into cell. Permeability of K+ is greater than Na+. Eq potential of K+ = 90mV

21
Q

what happens during a stimulus?

A

depolarisation, if it reaches a threshold value then an action potential is produced

22
Q

at the threshold potential, what happens to the permeability of the membrane to sodium?

A

increases permeability

23
Q

What happens during upstroke?

A

VGSC open quickly, sodium enters cell, VGPC open slowly, potassium leaves cell. Membrane potential moves towards Na+ equilibrium potential.

24
Q

what happens during repolarisation?

A

Sodium channels inactivated (plug stops flow), Na+ entry stops. More K+ channels open and remain open as K+ moves down its electrochemical gradient. Membrane potential moves towards K+ equilibrium potential

25
Q

what happens during the absolute refractory period?

A

nerve cannot be restimulated as sodium channels are inactivated, sodium cannot exit cell.

26
Q

what happens during hyperpolarisation?

A

K+ channels still open and K+ continues to leave cell down electrochemical gradient. As membrane potential reaches closer to K+ equilibrium, potential some K+ channels close. Membrane potential returns to resting.

27
Q

what is the name of the refractory period during hyperpolarisation?

A

relative refractory period

28
Q

what happens during the relative refractory period?

A

inactivation gate of Na+ channels opens, so a stronger than normal stimulus is needed to stimulate an action potential

29
Q

what happens to the decay in action potential depending on the diammeter / myelation of the neuron and why?

A

slower decay with a larger diammeter or small myelinated neuron because there is lower resistance

30
Q

at what speed does an action potential flow in a small diammeter, non myelinated axon?

A

1m/s

31
Q

at which speed does an action potential spread in a large diammeter, myelinated axon?

A

120m/s

32
Q

what can decrease conduction velocity?

A
  • reduced axon diammeter eg. regrowth after injury
  • reduced myelination eg. multiple sclerosis and diptheria, cold, anoxia, compression and drugs (some anaesthetics)
33
Q

what are the three main factors that influence the movement of ions accross a membrane?

A
  • concentration of ion on both sides of the membrane
  • charge on ion
  • voltage accross membrane
34
Q

Why is the Na+ equilibrium potential -ve eg. -70mV and the K+ equilibrium potential +ve eg. +40mV, when both are positive ions?

A
  • More K+ inside, so tend to flow out
  • More Na+ outside, so tend to flow in
  • A potential of -70mV is needed to attract K+ and stop net outward flow
  • A potential of +40mV is needed to repel Na+ from entering the cell
35
Q

which ion is important for the upstroke and which is important for the falling portion of the action potential? In which directions do these ions move?

A

Na+ - in

K+ - out

respectively

36
Q

which factors influence the speed and propagation of an action potential along an axon?

A
  • myelination - linear relationship between conduction and myelin thickness
  • axon diammeter - lower resistance, ions move faster
  • Conduction velocity equivalent to square root of axon diammeter
37
Q

Which equation is used to calculate real membrane potential?

A

Goldman-Hodgkin-Katz equation

BRS (19 decks)

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