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What is the role of the intercalated disks in cardiac muscle cells?

allow changes in membrane potential to travel directly to neighbouring cells without the need for a chemical synapse


What makes cells excitable?

Difference in ion concentrations represents stored energy which powers excitable cells


When solutes are charged and the membrane is selectively permeable, there will be a conflict between chemical and electrical energy. True or false?



Action potentials of specialised myocytes and contractile myocytes are faster than neurons. True or false?

False - slower and rely on Ca2+ gated channels rather than Na+


A cardiac contractile cell fires an action potential only when it is depolarised to threshold. True or false?



Pacemaker cells can't fire APs in the absence of an external stimulus. True or false?



What are pacemaker potentials?

The slow depolarisation that leads up to each AP


In pacemaker cells and other cardiac muscle cells, electrical signals are caused by changes in plasma membrane ______ ________ brought about by the opening and closing of specific ion channels

ion permeability


In cardiac muscle, the most important permeability changes involve, K+, Ca2+ and Na+ respectively. True or false?

False - Na+, K+ and Ca2+ respectively


The intracellular fluid is rich in sodium, but poor in potassium and calcium in comparison to the extracellular fluid. True or false?

False - rich in potassium, poor in calcium and sodium


As membrane permeability to a particular ion increases, the membrane potential moves towards the equilibrium potential of that ion. True or false?



In intracellular fluid, the equilibrium potential of potassium is negative and is positive for calcium and sodium. What happens to the equilibrium potentials of each ion when there is an increase in permeability of them all?

Equilibrium potential of calcium and sodium becomes more positive
Equilibrium potential of potassium becomes more negative


What triggers electrical signals in pacemaker cells?

changes in permeability of ions


If the SA node is prevented from generating the electrical impulse, other components of the conductive system are able to take over. True or false?

True - ectopic pacemakers


What connects pacemakers and conducting cells of the heart to contractile cells?

Gap junctions


What four things do contractile myocytes contain?

sarcoplasmic reticulum


Sarcoplasmic reticulum contains stores of calcium. True or false?



What is the sequence of events for the electrical activity of pacemaker cells?

slow depol at start due to closing of K+ channels and opening of funny channels (Na+)
Initial depol triggers T-type Ca2+ channels to open
L-type Ca2+ channels open as threshold is reached
Depol triggers opening of K+ channels - leading to reducing in membrane potential
Reduction in membrane potential leads to closing of Ca2+ channels
Membrane repolarised as a result of reduction in ca2+ into cell and increase in potassium leaving cell


What is the sequence of events in electrical activity of cardiac contractile cells?

depolarisation of membrane triggers opening of Na+ channels
Na+ channels become inactivated but membrane potential only drops a small amount because inital depolarisation triggers closing of K+ channels and opening of L-type Ca2+ channels
There is a plateau period where K+ remain closed and Ca2+ channels remain open
Increase in K+ leaving cell as K+ channels open in response to depolarisation.
Ca2+ channels close so less Ca2+ enters cell - membrane repolarised
Resting potential restored where K+ is dominant to Na+ and Ca2+ - membrane potential is -90mV


When is contraction due to actin-myosin cycling enabled?

When cytosolic Ca2+ binds to troponin making it active and capable of interacting with myosin


The fall in cytoplasmic Ca2+ makes troponin inactive and the actin-myosin fibres relax. How does this happen?

After repolarisation, active transport of Ca2+ returns it to the sarcoplasmic reticulum and across the cell membrane to the extracellular fluid