| When the heart is relaxed, what is the potential difference the inside and outside of the cells is? | Negative inside - except for pacemaker cells |
| What are some differences between cardiac action potential and normal muscle action potential | Much longer due to plataeu sustained by many calcium channels
the length is crucial since it ensures that there is enough time for all heart cells to still be depolarised when the last cell starts its action potential |
| Why is Calcium concentration important | In the heart, the force generated in the cell is proportional to the calcium concentration ( tension is proportional to the intracellular calcium concentration ) |
| What is the role of Calcium during muscle contraction | VGCCs allow an influx of Calcium ions into cells across the plasma membrane by opening in response to an increase in membrane potential i.e. depolarisation
Calcium is also released rapidly by intracellular stores
Ca2+ inside the cell induces the release of more Ca2+ through ryanodine receptor channels ( RyR )
Calcium ions then bind to troponin to initiate contraction
Relaxation occurs when Ca2+ unbinds from troponin
Calcium is then pumped back into the sarcoplasmic reticulum for storage |
| Role of nodal cells | Non-contractile nodal cells
- Intrinsically initiate ion-dependent electrical events at regular intervals ( 60-80 per minute )
Ion-dependent electrical impulses propagate from the SA node to the AV node via the interventricular septum to the cardiac apex to initiate contraction of the contractile cardiomyocytes
- This spreads through the myocardium to produce a coordinated heartbeat |
| What is the approx resting membrane potential of myocardium | -90 mv |
| What are the different relative concentrations of inside and outside the cells of the 3 main ions | Na+ conc is higher outside
K+ conc is higher inside
Most anions in cells are large molecules |
| What is the difference between pacemaker action potentials and other action potentials | Pacemaker cells do not have fast Na+ channels hence only use Ca2+
This leads to it being much more slower |
| What does a steep pacemaker potential indicate in heart rate | High heart rate |
| What does a shallow pacemaker potential indicate in heart rate | Low heart rate |
| If the patient has hyperkalaemia, what maybe the effect on the pacemaker potential | It may make the cell more hyperpolarised hence would need to be more depolarised so more Na+ would be needed and could take longer time between intervals which could lead to arrythmias |
