Cardiac Cycle Flashcards
What does myogenic mean?
Means the heart can beat without input from nervous system
How does the heart contract?
Muscle cells (myocytes) in heart have electrical charge across membrane = polarised
- when this charge is reversed, it becomes depolarised, making them contract
Describe role of nodes in cardiac contraction
~ sinoatrial node produces electrical stimulation sent to atrial walls, causing atria to contract
~ signal passes down atrial septum, passing to atrioventricular node between both atria
~ AVN conducts the signal to ventricles, passes wave down bundle of nerves called the His
~ bundle of His transmits wave to base of the heart
~ electricity passes up Purkyne fibres from the His, allowing ventricles to push blood upwards
Where is the SAN located?
Wall of the right atrium
How do nodes generally generate electrical signal?
At rest nodes are polarised
Positive charge builds on inside and negative on outside of nodes, caused by a buildup of ions
When contraction occurs, nodes become depolarised —> positive ions move out of nodes stimulating a wave of electricity
How is the hearts electrical activity be monitored?
ECG
What is the name given to fast and slow heart rates?
Fast = tachycardia
Slow = bradycardia
Describe why the two types of irregular heart beat occur
- Atrial fibrillation —> atria beat faster than ventricles, due to SAN constantly forming (no distinct P or T waves)
- Ectopic heart beat —> early ventricular beat
Which waves in an ECG show which stage of the cardiac cycle?
P wave (initial small spike) —> SAN, atrial systole
QRS wave (large spike) —> AVN, ventricular systole
T wave (small bump/plateau, larger than P) —> diastole
What is the neuromuscular junction?
Point where motor neurone meets skeletal muscle fibres; transmits nerve impulses
Why are neuromuscular junctions required?
Many junctions across muscle ensure that contraction is synchronised, simultaneously stimulating action potential, making contraction fast + strong
Describe process at neuromuscular junctions
1- nerve impulse received at neuromuscular junction causing synaptic vesicles to fuse with presynaptic neurone + release acetylcholine
2- acetylcholine diffuses to post synaptic membrane of muscle fibre, altering permeability of Na ions
3- Na ions move into post synaptic membrane, causing depolarisation and contraction
4- acetylcholine broken down by acetylcholinesterase, ensuring muscle isn’t overstimulated
5- products choline and ethanoic acid (acetyl) diffuse back to presynaptic neurone; recombined w energy from mitochondria to form acetylcholine
