Electrical Activity of the Heart Flashcards
what is contraction of heart muscle stimulated by?
excitation contracting coupling
what is A?
T-tubule
what is B?
Actin
what is C?
myosin
what is D?
z-line
what is the process of a normal muscle contraction?
- action potential reaches cell and causes Na voltage channels to open
- cell depolarises and causes calcium to be released from sarcoplasmic reticulum
- calcium binds to troponin and starts the muscle contraction
where is actin anchored?
z line
what are T-tubules?
deep invaginations in the muscle membrane that interact with the organelles in the cell, such as the sarcoplasmic reticulum
what allows cardiac cells to act as one big cell?
intercalated disks
- gap junctions (electrical connection): allow cells to communicate to each other by using signalling molecules
- desmosomes (physical connection): prevent cells from separating during contraction
what are intercalated discs?
connect cardiac cells to allow them to work as a single functional organ
- gap junctions
- desmosomes
what are the differences between the action potentials of skeletal muscle and cardiac muscle?
action potential lasts for way longer in cardiac muscle
how long does the action potential last for in skeletal muscle and cardiac muscle?
2ms in skeletal muscle
250ms in cardiac muscle
what does the action potential lasting for ages in a cardiac cell allow?
calcium to enter from outside the cell as well as sodium, allowing regulation of contraction
what does the longer action potential allowing calcium and sodium to enter from outside the cell allow?
heart contraction to be stronger or weaker
refractory period is longer
which is cardiac and skeletal muscle has the longer refractory period?
cardiac muscle
what differences are there between cardiac and skeletal muscle due to cardiac muscle having a longer refractory period?
skeletal muscle contractions can add together and accumulate (tetanus) due to many action potentials being added to one another
cardiac muscle has to fully contract before it can be stimulated again and so they do not add onto each other
why is it important that the long refractory period of cardiac muscle mean tetanus cannot occur?
heart needs to fully contract and then relax to pump blood
what is tetanus?
sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a high rate
what do cardiac cells that have unstable resting membrane potentials act as?
pacemakers
what does having pacemakers allow a cell to do?
depolarise again quicker
is there a greater K+ concentration inside or outside the cell
inside
is there a greater Na+ concentration inside or outside the cell?
outside
is there a greater Ca2+ concentration inside or outside the cell?
Outside
what causes the resting membrane potential of a cell?
at rest K+ gated channels are open (leaky) which makes the cell more negative until equilbrium is rached at -90mV
what is the resting membrane potential (RMP) of cardiac muscle?
-90mV
what is the process of non-pacemaker action potential?
- resting membrane potential (high resting permeability to K+
- initial depolarisation (increase in permeability to Na+)
- plateau (increase in permeability to Ca2+, L-type, and decrease in permeability to K+)
- repolarisation (decrease in permeability to Ca2+ and increase in permeability to K+)
what causes the resting membrane potential in non-pacemaker cells?
high resting permeability to K+
what causes the initial depolarisation in non-pacemaker cells?
increase in permeability to Na+
what causes the plateau in non-pacemaker action potentials?
increase in permeability to Ca2+ (L-type)
decrease in permeability to K+
what causes the repolarisation of non-pacemaker action potential?
decrease in permeability to Ca2+
increase the permeability to K+
what are the 2 different kinds of calcium channels?
L-type
T-type
do L-type or T-type calcium channels let lots of calcium in?
L type
what cause the pacemaker potential (pre-potential) in a pacemaker action potential?
gradual decrease in permeability to K+
early increase in permeability to Na+
late increase in permeability to Ca2+ (T-type)
what causes the action potential in the pacemaker action potential?
increase in permeability to Ca2+ (L-type)
what does the pacemaker action potential of the heart explain?
autorhythmicity
what brings heart cells to action potential in the first place?
pacemaker action potential
how would you describe the difference between pacemaker and non-pacemaker cells?
not black and white, it is a spectrum
what is the pacemaker cell of the heart?
the one with the fastest rhythm, all cells around it take up this rhythm
what can electrical activity be modulated by?
- sympathetic and parasympathetic systems
- drugs
- temperature
- hyperkalemia
- hypokalemia
- fibrillation and heart block
- hypercalcemia
- hypocalcemia
what are examples of drugs that alter the electrical activity?
- Ca2+ channel blocker (decrease force of contraction)
- Cardiac glycocides (increases force of contraction)
what effect does Ca2+ channel blockers have on electrical activity?
decreases force of contraction
what effect does cardiac glycocides have on electrical activity?
increases force of contraction
what effect does temperature have on electrical activity?
increases about 10bpm per 1oC
what effect does hyperkalemia have on electrical activity?
fibrillation and heart block
what is hyperkalemia?
high plasma K+
what is hypokalemia?
low plasma K+
what effect does hypercalcemia have on electrical activity?
increased heart rate and force of contraction
what effect does hypocalcemia have on electrical activity?
decreased heart rate and force of contraction
what is hypercalcemia?
high plasma Ca2+
what is hypocalcemia?
low plasma Ca2+
what is fibrillation?
irregular heartbeat
what is heart block?
blocking action potentials getting from the atrium to the ventricles
what does the special conducting system ensure?
both atriums and ventricles contract at the same time
what is A?
superior vena cava
what is B?
sinoatrial node
what is C?
right atrium
what is D?
right bundle branch
what is E?
right ventricle
what is F?
purkinje fibres
what is G?
inferior vena cava
what is H?
left bundle branch
what is I?
left ventricle
what is J?
left atrium
what is K?
bundle of His
what is L?
atrioventricular node
what is the process of the activation of the special conducting system?
- sinoatrial node (about 0.5m/s)
- atrioventricular node (about 0.05m/s, acts as a delay)
- bundle of His
- purkinje fibres (about 5ms, acts as a rapid conducting system)
what do the left and right bundles of His break down into
purkinje fibres
what do purkinje fibres ensure?
all of the ventricle contracts at the same time
why is the delay of the atrioventricular node required?
so the atrium can get as much blood as possible into the ventricles
what is the wave seen on an electrocardiogram?
summation of little action potentials in individual myocytes
what is an electrocardiogram?
test used to check hearts rhythm and electrical activity
what is A?
P wave
what is BCD complex?
QRS complex
what is E?
T wave
what does the P wave correspond to?
atrial depolarisation
what does the QRS complex correspond to?
ventricular depolarisation
what does the T wave correspond to?
ventricular repolarisation
