Physiological properties of the heart Flashcards
What is a syncitium?
A multinucleated cell
What percentage of cardiac fibres do not contract?
1%
What is the effect of the parasympathetic nervous system on the rate of SA node depolarisation?
Decreases rate of SA node depolarisation
What is the effect of the sympathetic nervous system on the rate of SA node depolarisation?
Increases rate of SA node depolarisation
What is the intrinsic pacemaker of the heart?
The Sinoatrial node
How long is the cardiac cycle roughly?
0.6 - 1 second
What is the resting potential of cardiac muscle?
Roughly -90 mV
What is the ratio of K+ to Na+ inside the cell?
K+ exceeds Na+ by 50:1
What is the effect of sympathetic stimulation affect on cyclic AMP production?
Increases cAMP production
Sympathetic stimulation increases what ion concentrations?
Ca2+ and Na+ (Na+ via ‘funny’ channels)
What is a positive chronotropic effect?
An increase in heart rate
What is a positive ionotropic effect?
Increase the strength of muscular contraction (stroke volume)
What does phase 0 of ventricular depolarisation involve?
Rapid depolarisation due to an increase in Na+ permeability as fast Na+ channels open
What does phase 1 of ventricular depolarisation involve?
Start of repolarisation as fast Na+ channels close
What does phase 2 of ventricular depolarisation involve?
Effect of Ca2+ entry via L-type [DHP] channels
What does phase 3 of ventricular depolarisation involve?
Rapid repolarisation as increase Ca2+ concentration stimulates K+ channels to open and increase K+ permeability
What does phase 4 of ventricular depolarisation involve?
Stable resting membrane potential where K+ exceeds Na+ by 50:1
Symapthetic stimulation effects what type of receptor?
NA acts on B1 recptors to increase cAMP production
Parasympathetic stimulation effects what type of receptor?
Ach acts of M2 receptors which decrease cAMP production
Parasympathetic stimulation affect on membrane potential?
Hyperpolarises membrane potential to lower starting level.
Parasympathetic stimulation increases what ion concentration?
K+ concentration increases due to an increase in extent and duration of opening of K+ channels
An increase in Ca2+ causes an increase in what?
stroke volume
An increase in Na+ causes an increase in what?
Heart rate
What is Einthoven’s triangle?
Einthoven’s triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis.The shape forms an inverted equilateral triangle with the heart at the center that produces zero potential when the voltages are summed.
What is the rate of depolarisation of the SA node?
90/min
What is the rate of depolarisation of the AV node?
60/min
What is the rate of depolarisation of the bundle of His?
50/min
What is the rate of depolarisation of the purkinje fibres?
40/min
What is the rate of depolarisation of the ventricles?
30/min
