| define myogenic | a characteristic of cardiac muscle where it can initiate its own contraction without nervous stimulation |
| what is the SAN? | sinoatrial node
found in the right atrium
initiates heart contraction by regularly producing action potentials |
| what is the AVN? | atrial ventricular node
found in the septum of the heart
recieves impulses from SAN and transmitts to Bundle of His after a short delay |
| what are the Bundle of His? | bundles of cardiac cells
carry the electrical impulse from the AVN and transmitt to the purkinje fibres |
| what are the Purkinje fibres? | bundles of cardiac cells
carry electrical impulses from the Bundles of His upward through the ventricles causing contraction from the bottom up |
| describe how depolarisation spreads through the heart | SAN is stimulated by the autonomic nervous system
SAN depolarises
depolarisation spreads into the atria and the atria contract
depolarisation spreads to the AVN and passes down the Bundle of His
depolarisation reaches the apex of the heart
the electrical impulses pass through the purkinje fibres
ventricles contract from the bottom up |
| why is there a delay between atrial diastole and ventricular systole? | the ventricles are filling up with blood |
| why cant depolarisation spread directly to the ventricles ? | they have a region of non conductive tissue |
| what causes the change in electrical activity in the heart? | the wave of depolarisation |
| what is an ECG? | electrocardiogram
detects and measures electrical changes to regions of the heart
can be used to diagnose heart diseases
signals are shown as waves on a computer |
| what are the parts of an ECG? | P wave
PR interval
PR segment
QRS complex
QT interval
ST segment
T wave |
| what does the P wave represent? | depolarisation of the atria |
| what does the PR interval represent? | the time between atrial depolarisation and ventricular depolarisation |
| what does the PR segment represent? | the delay of electrical impulse to reach the AVN from the atria |
| what does the QRS complex represent? | ventricular depolarisation |
| what does the QT interval represent? | the time taken for the depolarisation and repolarisation of the ventricles |
| what does the ST segment represent? | the beginning of ventricular repolarisation |
| what does the T wave represent ? | ventricular repolarisation |
| calculate cardiac output | cardiac output = stroke volume x heart rate |
| what is cardiac output? | the volume of blood pumped by the heart into the circulatory system in 1 min
measured in litres per minute (L/min) |
| what is stroke volume? | the volume of blood pumped out of the left ventricle each time the heart beats
measured in millilitres per square metre (ml/m²) |
| what is heart rate? | number of cardiac cycles per minute
measured in beats per minute (BPM) |
| what is ventilation rate? | volume of air breathed in or out in a minute
measured in litre per second (l/s) or cubic meter per hour or (m³/hr) |
| calculate ventilation rate | ventilation rate = tidal volume x number of breaths per minute |
| define tidal volume (Vt) | the volume of air that moves in or out the lungs with each respiratory cycle |
| what factors increase heart rate? | low pH
stretch receptors
decrease in blood pressure
adrenaline |
| what are baroreceptors? | sensors that are sensitive to pressure changes
found in the sinuses of the carotid artery in the neck and aortic arch |
| what are stretch receptors? | monitor the length and velocity of muscle movement
found all over the body |
| what are chemoreceptors? | sensitive to changes in CO2 and pH
found in the medulla and carotid arteries in the neck and aortic arch |
| what two ways can the heart rate be controlled? | nervous and hormonal |
| nervous control of heart rate when blood pressure increases | bp increases
baroreceptors stretch
signal is sent to the cardiovascular control centre in the medulla
a signal is sent by the parasympathetic nerve
the SAN does not depolarise
the heart rate decreases |
| nervous control of heart rate when CO2/pH changes | CO2 in blood increases/pH decreases
chemoreceptors detect the change
a signal is sent to the CV control centre in the medulla
a signal is sent by the sympathetic nerve
SAN depolarises
heart rate increases |
| parasympathetic nerve | vagus nerve
inhibitory
connects the SAN and the medulla
slows heart rate down |
| sympathetic nerve | exitatory
speeds heart rate up |
