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level: Level 1

Questions and Answers List

level questions: Level 1

QuestionAnswer
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 potentialMuch 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 importantIn 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 contractionVGCCs 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 cellsNon-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 ionsNa+ 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 potentialsPacemaker 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 rateHigh heart rate
What does a shallow pacemaker potential indicate in heart rateLow heart rate
If the patient has hyperkalaemia, what maybe the effect on the pacemaker potentialIt 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