HEART RATE Flashcards
effect of adrenaline
direct effect on SAN to increase HR (anticipatory rise)
causes dilation of arterioles supplying skeletal muscles
constricts arterioles going to digestive system/ non essential organ
maximise blood flow to active muscles
sympathetic
stimulation of sympathetic nerves prepares body systems for action (fight or flight)
parasympathetic
stimulation controls the body’s systems when resting and digesting
cardiovascular control centre
controls the HR
locate in medulla oblongata region of brain
detects accumulation of CO2, lactate in blood, reduction of oxygen and increased temperature
cardiovascular control centre to heart
nerves: sympathetic nerve (accelerator), vagus nerve (parasympathetic)
role of nerves in heart
sympathetic nerve stimulates the SAN to cause an increase in HR
impulses from vagus nerve slow down the HR
stimulus -> change in HR
stimulus
contraction of skeletal muscles
stimulation in stretch receptors in muscles and tendons
send impulses to cardiovascular control centre
raises HR via sympathetic nerve
increase in venous return
rise in stroke volume
rise in HR and SV together result in higher cardiac output
higher cardiac output
caused by rise in HR and SV together
causes quicker transportation of oxygen and fuel to muscles
blood pressure rises
effect of cardiac output on blood pressure
BP rises with higher cardiac output
pressure receptors in aorta and carotid artery send nerve impulses back to cardiovascular control centre to prevent BP rising too far
inhibitory nerve impulses sent CCC to SAN
excessive rise in BPP is avoided by negative feedback (prevents a further rise in HR)
myogenic nature of heart
can contract without external stimulation
contraction initiated by small changes in electrical charge of cardiac muscle cells
depolarisation of heart
starts at sinoatrial node
SAN generates electrical impulse which spreads across the right and left atria
causes right and left atria to contract simultaneously
impulse travels to atrioventricular noe
- impulse conducted to ventricles after short delay
signal reaches purkyne fibres
branches carry impulse to inner cells of the ventricle an spreads through ventricle walls
sinoatrial node
specialised muscle fibres in right atrium
known as pacemaker
purkyne fibres
large, specialised muscle fibres that conduct impulses rapidly to the apex of the ventricles
right and left bundles collectively called Bundle of His
fibres continue around each ventricle and divide into smaller branches that penetrate the ventricular muscle
contraction of heart
first ventricular cells to be depolarised are at the apex of the heart
contraction begins at apex and travels upwards toward atria
produces wave of contraction up the ventricle
pushes blood into aorta and pulmonary artery
ECG
measures and displays electrical activity of heart during cardiac cycle
ECG method
electrodes attached to chest and limbs to record electrical currents produced
when there is a change of polarisation in heart, small electrical current can be detected on skin surface
ecg measures this current on skin
p wave
shows depolarisation of the atria
QRS complex
wave of depolarisation resulting in contraction of the ventricles (ventricular systole)
hides the small signals of atrial repolarisation
PR interval
time taken for impulses to be conducted from the SAN across the atria to the ventricles, through the atrioventricular node
T wave
repolarisation of the ventricles during the heart’s relaxation phase
bradycardia
HR less than 60bpm
could be symptoms of heart problems/ or common healthy heart in athletes
tachycardia
HR greater than 100bpm
result of anxiety/ fear/ fever/ exercise
could be symptom of coronary heart disease/ heart failure/ use of medicines/ drugs/ fluid loss/ anaemia
