cardiac electrophysiology

Question 1

cardiac myocyte structure

Answer 1

each myocyte is bound by an intercalated disc which helps stabilise the structure and hold everything close together.
gap junctions allow ions and small molecules to move from one cell to another and allow electrical connection transmissions.

Question 2

cardiac cell structure

Answer 2

single celled nucleus and attached end to end with intercelated discs, they contain lots of mitochondria to help provide energy. connections through desmosomes and gap junctions. electrically continuous, consists of myofibril likle units.

Question 3

transverse tubular system

Answer 3

each fibre is surrounded by sarcolemma. deep invaginations opposite the T tubules allow depolarisation. T tubules help activate the myofibrils

Question 4

sarcoplasmic reticulum

Answer 4

passes close to sarcolemmal surface and T tubules. stores and pumps calcium ions, high content of calcium ions, involved in the release of calcium ions when activated.

Question 5

myofibril and sarcomere

Answer 5

sarcomere is the contractile unit, thick filament myosin (A band) and thin filament troponin and tropomyosin (I band) overlap when contracts.

Question 6

thick and thin filament

Answer 6

thick filament myosin A band has head and tail, the head contains actin binding site. thin filament actin I band , trpomyosin and troponin, 2 entwined actin filaments, carried on a tropomyosin molecule.

Question 7

sliding filament theory

Answer 7

H band and I band gets smaller, Z lines get closer, myofibril gets shorter.

Question 8

cardiac cell ion concentrations

Answer 8

inside the cell there is a negative electrical charge compared to the outside. the voltage difference means a transmembrane potential. high potassium concentration within the cell, low outside so diffuses outwards. low sodium and calcium ions in the cell and high outside of cell so diffuses inwards. cardiac cells are excitable due to the negative charge in the cell. cell membrane open when excited, allowing movement of ions which chnages the transmembrane potential.

Question 9

SA note action potential

Answer 9

no true resting potential, has no plateu at the bottom, its threshold is -40 so when it hits that it will spike its action potential. its depolarising current is calcium currents. has no fast sodium channel, has unstable resting potential. the steeper the slop of 4, the faster the heart rate.

Question 10

ventricular action potential

Answer 10

phase 4 when resting is at -90, potassium channels open and poatssium currents are high. fast sodium channels and slow calcium channels are closed.

Question 11

Difference SA and VA

Answer 11

both have slow depolarisation at phase 0. dependant on slow calcium channels for depolarisation.