Lesson 2: Regulation of Cardiac function
Cardiac muscle action potential
- Depolarisation - opening of sodium ion channels (can be blocked by lidocaine)
- Plateau - opening of calcium ion channels (can be blocked by verapamil and
dihydropyridines)
- Repolarization - voltage gated potassium ion channels
- Tetanus is continuous contraction of the muscle
- Long cardiac action prevents tetany and prevents against reentrant arrhythmias
Heartbeat conduction
- Action potential of ventricular muscle has a faster upstroke then the SAN
- Ventricular muscle cells are more stable and have a negative potential compare to
the atrial cells which are less stable and have a higher voltage
SAN action potential - depolarisation triggered by the opening of calcium ion channels
which enter into cardiac nodal cells (membrane potential becomes more positive).
Repolarisation triggered by potassium ion channels.
- Decay rate of pacemaker potential determines the heat rate
- Noradrenaline increases the decay rate
- Adrenaline decreases decay rate and causes hyperpolarization
, Conduction Pathway
1. SAN in the atrium walls
2. AVN (slower as atria contract before ventricles)
3. Bundle of His
4. Purkinje Fibres
Epicardium - outer layer of heart
Endocardium - inner lawyer of the heart
How is the signal transmitted between cardiac cells:
- Myocytes are cardiac cells which are found in the myocardium in the middle layer of
the heart
- Between 2 cell membranes are the intercalated discs
- In the intercalated disc you find the desmosome (structural integrity and joining
myocytes together), gap junction (electrical signal between two myocytes) and
connexons (pores which allow the signal to cross between cells)
- Only muscle cells take place in conduction not nerve cells
- Redundancy in system
Cardiac muscle action potential
- Depolarisation - opening of sodium ion channels (can be blocked by lidocaine)
- Plateau - opening of calcium ion channels (can be blocked by verapamil and
dihydropyridines)
- Repolarization - voltage gated potassium ion channels
- Tetanus is continuous contraction of the muscle
- Long cardiac action prevents tetany and prevents against reentrant arrhythmias
Heartbeat conduction
- Action potential of ventricular muscle has a faster upstroke then the SAN
- Ventricular muscle cells are more stable and have a negative potential compare to
the atrial cells which are less stable and have a higher voltage
SAN action potential - depolarisation triggered by the opening of calcium ion channels
which enter into cardiac nodal cells (membrane potential becomes more positive).
Repolarisation triggered by potassium ion channels.
- Decay rate of pacemaker potential determines the heat rate
- Noradrenaline increases the decay rate
- Adrenaline decreases decay rate and causes hyperpolarization
, Conduction Pathway
1. SAN in the atrium walls
2. AVN (slower as atria contract before ventricles)
3. Bundle of His
4. Purkinje Fibres
Epicardium - outer layer of heart
Endocardium - inner lawyer of the heart
How is the signal transmitted between cardiac cells:
- Myocytes are cardiac cells which are found in the myocardium in the middle layer of
the heart
- Between 2 cell membranes are the intercalated discs
- In the intercalated disc you find the desmosome (structural integrity and joining
myocytes together), gap junction (electrical signal between two myocytes) and
connexons (pores which allow the signal to cross between cells)
- Only muscle cells take place in conduction not nerve cells
- Redundancy in system
