Electrical Activity In The Heart Flashcards

0
Q

What are the intracellular and extra cellular concentrations of potassium ?

A

Intracellular = 150mM
Extra cellular = 5mM
30 fold difference

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1
Q

What is the intracellular and extra cellular concentrations of sodium ?

A

Intracellular = 15mM
Extracellular = 150mM
10 fold difference

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2
Q

What is the intracellular and extra cellular concentrations of calcium ?

A

Intracellular = 0.0001mM
Extra cellular= 2mM
20000 fold difference

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3
Q

What is the Nernst equation ?

A

It transduce the concentration gradient of an ion into a potential

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4
Q

How do we know that the resting membrane potential is mainly permeable to potassium ions ?

A

Because the resting membrane potential is negative and the only ion which produces a negative equilibrium potential is potassium so membrane potential is dominated by potassium concentrations

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5
Q

What are the properties of cardiac ions channels for sodium ?

A

They are fast voltage gated sodium channels
Open at negative voltages - -50mV
Activates rapidly but inactivates rapidly
Produces an inward current

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6
Q

What are the properties of cardiac ion channels for potassium ?

A

Produce an outward current
BACKGROUND POTASSIUM CHANNELS
- open at negative voltages and set the negative resting membrane potential of atrial and ventricular muscle
- they close at positive membrane potentials
DELAYED POTASSIUM CHANNELS
- they are closed at negative membrane potentials
- open at more positive membrane potentials because they are involved in repolarisation of the cell

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7
Q

What are the properties of cardiac ion channels for calcium ?

A
T-TYPE - transient opening / tiny conductance 
- mainly in pacemaker and atrial tissue 
- open at -55mV 
- inactivate rapidly 
L-TYPE - large conductance/long lasting opening 
-found throughout the heart 
- open at -40mV 
- inactivate slowly
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8
Q

What are the properties of mixed conductance channels ?

A

1- BACKGROUND SODIUM CONDUCTANCE
- small conductance of sodium and potassium
- their reversal potential is -20mV
- makes inward currents at potentials negative to the -20mV
2- FUNNY CURRENT
- permeable to both sodium and potassium
- activates slowly but has small conductance
- their reversal potential is -20mV
- present in he SAN
- called the funny current because they are the only channels opened by hyper polarisation

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9
Q

Why is there no stable resting membrane potential in the SAN ?

A

Because there are no background potassium channels present so ten resting potential is continually changing

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10
Q

What are the 4 overlapping currents which make up the pacemaker potential ?

A

1- decay of delayed potassium channel permeability
2- funny current
3- background sodium conductance
4- T-type calcium channels

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11
Q

What is the pacemaker potential ?

A

It is the period between action potentials

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12
Q

What induces repolarisation in the SAN action potential ?

A

Induced by closure of L-type calcium channels and opening of delayed potassium channels

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13
Q

Why does ventricular action potential have a stable resting potential ?

A

Because there are background potassium channels present

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14
Q

What is responsible for the depolarisation in the ventricular action potential ?

A

Opening of voltage gated sodium channels allowing sodium to enter the cell

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15
Q

Which channels are responsible for the plateau phase of the ventricular action potential ?

A

L-type calcium channels which open at -40mV

The inward current is long lasting

16
Q

Which channels are responsible for the repolarisation of the ventricular action potential ?

A

Opening of the delayed potassium channels and the closing of the the L-type calcium channels

17
Q

What is the hierarchy of pacemakers ?

A

SAN, AVN and purkinje fibres

18
Q

Why can’t ions cross the membrane and how do they ?

A

Because they are charges

To be able to cross they need an aqueous environment which is produced by specific protein ion channels