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Action Potentials Flashcards

(25 cards)

1
Q

What are the 3 electrical properties of excitable cells?

A

Resistance; current and voltage

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2
Q

Why do all cell have membrane potential

A

Have varying concentration of ions in cells and are selectively permeable to some of them hence some ions move out of membrane and some cannot and vice versa.

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3
Q

What happens when a state of electrochemical equilibrium is reached?

A

When electrical repulsion forces equals chemical attraction forces(due to diffusion).

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4
Q

What is equilibrium potential?

A

Potential when electrochemical equilibrium is reached

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5
Q

In the Nernst Equation, what is the value of RT/F

And z

A

-61

Z= charge of ion

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6
Q

In the Nernst equation what is represented by concentration on the numerator of log

A

Intracellular concentration

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7
Q

What are the extracellular and intracellular concentration of sodium ions

A

Extra- 150mM

Intra- 10mM

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8
Q

What are the extracellular and intracellular concentration of potassium ions

A

Extra- 5mM

Intra- 150mM

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9
Q

Na- 72mV; K= -90mV; why doesn’t the membrane potential rest at either values?

A

The cells have varying amount of sodium and potassium channels that are open; more potassium channels that are open than odium

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10
Q

What does the Goldman-Hodgkin-Katz equation describe

A

Membrane potential of cells taking account of channels that are open and closed

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11
Q

In the GHK equation, what are the conditions for which normal resting potential is reached?

A

K channels- always open
Cl- channels- always closed
Na+ channels - open 5% of the time

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12
Q

What are the 4 different types of changes in membrane potential?

A

Depolarisation- potential moves towards zero
Repolarisaiton- more negative towards resting potential
Overshoot- above zero
Hyperpolarisation - more negative below resting potential

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13
Q

What causes graded potentials?

A

Caused by stimulation-
Occurs in synapses and sensory receptors
Contribute to initiating/ preventing action potentials

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14
Q

Why is there a decremental spread in action potential down the axon

A

Charge leaks out

Leakage depends on size of axon and stimulus

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15
Q

What determines the permeability of ion channels in an action potential

A
Permeability depends on conformational state 
Depolarisation - opened
Sustained depolarisation - inactivated 
Hyperpolarisation- closed 
Repolarisation?
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16
Q

Apart form neurones and muscle cells where else can action potential be generated

A

In some endocrine tissue

17
Q

Compare the permeability of both VG channels during upstroke

A

VGNa+ open quickly

VGK+- open slowly

18
Q

Describe what happens during repolarisation

A

VGNa+ - closed-

More VGK+ open quickly

19
Q

What else happens at the start of Repolarisation

A

Absolute refractory period
Activation gate open
Inactivation plug (gate)- closed

20
Q

What happens at the end of repolarisation

A

Absolute refractory period continue

Activation and inactivation gate closed

21
Q

What happens after hype-polarisation

A

Relative refractory period
Activation gate closed
Inactivation plug open; strong stimulus can trigger action potential.

22
Q

What restores resting potential after AP; compare speed

A

NORMAL (NOT VG)ion channels (fast)

Ions pumps - slow

23
Q

What occurs during passive propagation of action potential

A

ONLY resting K+ channels are open.

Resistance alters propagation distance.

24
Q

Where are VG channels located in myelinated axons

A

At Nodes of Ranvier

25
What affects conduction velocity
Axon diameter Myelination Temperature Oxygen