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Neurology > Membrane and Action Potentials > Flashcards

Membrane and Action Potentials Flashcards

1
Q

What are the properties of diffusion?

A

Over short distances
Spontaneous
No energy input required

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2
Q

What is flux?

A

The number of molecules that cross a unit area per unit of time

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3
Q

What is voltage?

A

Potential difference

Generated by ions to produce a charge gradient

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4
Q

What is current?

A

Movement of ions due to a potential difference

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5
Q

What is resistance?

A

Barrier that prevent the movement of ions

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6
Q

How do we measure membrane potential?

A

A reference electrode is place outside the cell (Zero volt level)
Another electors places inside the cell
Measures voltage difference that is negative compared with outside

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7
Q

Why do we need ion channels?

A

Lipid cell membrane is a barrier to ion movement

Channels can be selective for different types of ion

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8
Q

What is electrochemical equilibrium?

A

Achieved the electrical force prevents further diffusion across the membrane

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9
Q

How can equilibrium potential be calculated?

A

The Nernst equation

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10
Q

What are typical concentrations of K+?

A

150mM inside

5mM outside

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11
Q

What are typical concentrations of Na+?

A

10mM inside

150mM outside

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12
Q

What is the equilibrium potential for K+?

A

Ek= -90mV

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13
Q

What is the equilibrium potential for Na+?

A

ENa= +72mV

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14
Q

Why do membrane potentials not set at EK or ENa?

A

Membranes have mixed K+ and Na+ permeability

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15
Q

How can we describe resting membrane potential?

A

The Goldman-Hodgkin-Katz (GHK) equation

Takes into account K+/Na+/Cl- concentrations

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16
Q

Define depolarisation

A

Membrane potential increases from negative towards 0mV

17
Q

Define repolarisation

A

Membrane potential decrease towards resting potential (becomes more negative)

18
Q

Define overshoot

A

Membrane potential becomes more positive

19
Q

Define hyperpolarisation

A

Membrane potential decreased beyond resting potential

20
Q

What are graded potentials?

A

Change in membrane potential in response to stimulation
Occurs at synapses an in sensory receptors
Contribute to initiating or preventing action potentials

21
Q

What happens as an impulse propagates?

A

Charge leaks

22
Q

In what cells do action potentials occur in?

A

All excitable cells
Mainly neutrons and muscle cells
Also some endocrine tissues

23
Q

What does permeability of the membrane depend on?

A

Conformational state of ion channels

24
Q

What does the conformational state of ion channels depend on?

A

Opened by membrane depolarisation
Inactivated by sustained depolarisation
Closed by membrane hyper-polarisation/ repolarisation

25
Q

What are the 5 phases of action potential?

A 
Resting membrane potential 
Depolarising stimulus
Upstroke
Repolarisation 
After-hyperpolarisation
26
Q

What’s the deal with Phase I?

A

Permeability for K>Na

27
Q

What’s the deal with Phase II?

A

The stimulus depolarise the membrane potential

Moves it in the positive direction towards threshold

28
Q

What’s the deal with Phase III?

A

Starts at threshold potential
Na+ channels open quickly and Na+ enter cell
K+ channels open slowly and K+ leaves the cell

29
Q

What’s the deal with Phase IV?

A

VGSC close and Na+ entry stops
More VGKC open and remain open
K+ leaves cell

Absolute refractory period

30
Q

What’s the deal with Phase V?

A

VGKC are still open
K+ continuaste leave the cells down electrochemical gradient
Membrane potential moves close to K+ equilibrium
Some VGKC’s close
Membrane potential returns to resting potential
Relative refractory period

31
Q

What’s the deal with passive propagation?

A

Only resting K+ channels open

Internal and membrane resistance alters propagation distance and velocity

32
Q

How is an AP propelled down the axon?

A

Active area at peak of AP

Local current flow depolarises adjacent region toward threshold

33
Q

Where are VGCs mainly found?

A

At nodes

34
Q

What influences conduction velocity?

A

Axon diameter
Myelination
Reduced with reduced diameter and myelination

Cold
Anoxia
Compression
Drugs

35
Q

Wh

A

Concentration of the ion on both sides of the membrane
Charge on the ion
Voltage across the membrane

Neurology (19 decks)

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