cardiac physiology

Question 1

is the resting membrane potential negative or positive

Answer 1

negative

Question 2

what functional response does an action potential cause

Answer 2

nerve impulse or muscle contraction

Question 3

what is an action potential generated by

Answer 3

rapid changes in electrochemical gradients across the cell membrane like movement of ions

Question 4

what is the movement of ions in and out of the cell controlled by

Answer 4

specific ion channels embedded in the membrane

Question 5

name the 3 ions involved in membrane potential

Answer 5

K+, Na+, Ca2+

Question 6

what is depolarisation

Answer 6

membrane potential gets less negative

Question 7

what is depolarisation in muscles

Answer 7

membrane potential goes positive

Question 8

what is repolarisation

Answer 8

potential returns to negative resting potential

Question 9

what is hyperpolarisation

Answer 9

membrane potential becomes more negative than resting potential

Question 10

how to detect and monitor action potentials generated by myocytes

Answer 10

electrocardiogram (ECG)

Question 11

what is excitation-contraction coupling and how is it achieved

Answer 11

-process which an electrical action potential leads to cardiac muscle cells contracting

-achieved by converting a chemical signal into mechanical energy via contractile proteins

Question 12

what is contraction of actin and myosin filaments dependent on

Answer 12

calcium signalling

Question 13

what do gap junctions do

Answer 13

link cytoplasm of neighbouring cells and enable rapid passage of ions/small molecules

Question 14

structural features of myocardium that help membrane potential changes

Answer 14

intercalated discs- tight interactions, electrical coupling, branched to extend interconnections, single nucleus, lots of mitochondria

synchronised contractions- ensures cardiomyocytes work together, syncytium cardiac muscle

gap junctions- enable rapid passage of ions/small molecules

Question 15

how do intercalated discs facilitate membrane potential changes

Answer 15

enable tight interactions and help electrical coupling, branched fibres to extend interconnections, single nucleus, abundance of mitochondria

Question 16

describe the pathway of intrinsic waves of excitation

Answer 16

SA node to AV node to myocytes to bundle of His and purkinje fibres

Question 16

which node is also called the cardiac pacemaker

Answer 16

sinoatrial node

Question 16

what does the AV node do after receiving signals from the SA node

Answer 16

passes signals to bundle of His, depolarises both ventricles, branches out

Question 16

how does the sinoatrial node cause an action potential

Answer 16

excites the right atrium then the left atrium then the atrioventricular node

Question 16

autorhythmic cells are also called

Answer 16

pacemaker cells

Question 16

what controls sinoatrial activity

Answer 16

autonomic nervous system signals

Question 16

what does the influx of K+ cause

Answer 16

repolarisation

Question 16

what does the influx of CA2+ cause

Answer 16

depolarisation of SAN

Question 16

what does the influx of Na+ cause

Answer 16

depolarisation of cardiomyocytes

Question 16

describe the action potential in autorhythmic/pacemaker cells

Answer 16

-no external stimulation to initiate action potential, undergoes spontaneous depolarisation when threshold is met

1.slow depolarisation caused by Na+ leaving cell faster than K+ through If channels

2.CA2+ channels open as membrane approaches threshold, causes more rapid depolarisation

3.K+ channels open causing efflux of K+ and membrane repolarises

Question 17

describe the general shape of the graph of action potential of pacemaker cells and list the stages

Answer 17

slow depolarisation, action potential, repolarisation
graph-see notes

Question 17

what does efflux mean

Answer 17

movement out of cell

Question 17

describe the action potential of cardiomyocytes (contractile system)

Answer 17

resting phase- resting potential (-90mV) due to constant leak of K+, sodium and calcium channels closed

depolarisation- NA+ channels open and ions enter, depolarises inside cell (cell gets more positive inside), causes action potential

early repolarisation- cell is slightly positive, outward flow of K+ returns transmembrane potential to 0

plateau phase- K+ leave cell via delayed rectifier K+ channels, CA2+ go in cell, electrically balanced, tmp maintained at a plateau below 0 mV (refractory period)

repolarisation- CA2+ channels inactivated (no more going in cell), more K+ leaving cell so cell gets more negative

Question 17

describe the general shape of the graph of action potential of cardiomyocytes and list the stages

Answer 17

resting, depolarisation, early repolarisation, plateau, repolarisation

graph- see notes