elastic properties of the heart

Question 1

List the sequence events occurring during excitation-contraction coupling in cardiac muscle.

Answer 1

cardiac muscle forms a functional syncytium electrically connected by gas junctions and physically connected by desmosomes which form intercalated discs. Long refractory period so can’t exhibit tetanic contractions. calcium entry from outside the cell regulates contractions. calcium release doesnt saturate troponin so regulation can be used to vary strength of contraction

Question 2

Compare the basis of the action potential in pacemaker and non- pacemaker tissue.

Answer 2

non-pacemaker cells undergo very rapid depolarisation as a result of opening sodium channels
pacemaker cells spontaneously depolarise and its due to movement of calcium ions

Question 3

why does cardiac muscle have a long action potential

Answer 3

-250ms compared to -2 in skeletal muscle. Long refractory period so cannot exhibit tetanic contraction. calcium entry from outside cell can regulate contraction and regulate the strength of contraction

Question 4

non pacemaker action potential

Answer 4

High resting permeability to potassium ions. Cell then depolarises due to an increase in permeability to sodium. Channels close quickly and plateau occurs due to increase in permeability to calcium (L-type) and decrease on permeability to potassium. Repolarisation occurs due to decrease in permeability to calcium and increase in PK+

Question 5

Pacemaker action potential

Answer 5

first reason cells depolarise is because of this gradual decrease in permeability of the cell to potassium. Increase in PNa (IF channels) and late increase in Pca (t-type) (don’t let much calcium in) Action potential due to an increase in PCa (L-type)

Question 6

Role of Sinoatrial node

Answer 6

The sinus node continuously generates electrical impulses, thereby setting the normal rhythm and rate in a healthy heart. (-0.5)m/s

Question 7

role of annulus fibrosis

Answer 7

Annulus fibrosis- ring of non conducting tissue. Spreads through Atrioventricular node and acts as a delay box and allows atria time to depolarise and contract

Question 8

role of atrioventricular node

Answer 8

an electrical gatekeeper between the atria and ventricles and introduces a delay between atrial and ventricular excitation, allowing for efficient ventricular filling

Question 9

Bundle of His and Purkinje fibres

Answer 9

The bundle of His is a heart muscle that takes part in electrical conduction in the heart. Purkinje fibres are branched fibres that carry the electrical impulse to the ventricles.

Question 10

what happens to an action potential in a single myocyte

Answer 10

Evokes a very small extracellular electrical potential, however lots of small extracellular potentials evoked by many cells depolarising and depolarising can summate to a large extracellular electrical wave

Question 11

what is the p wave

Answer 11

atrial depolarisation

Question 12

what is the QRS complex

Answer 12

vertricular depolarisation

Question 13

what is the T wave

Answer 13

Ventricular repolarisation