Control Of Heart Rate Flashcards
1
Q
Myogenic
A
- heart cells initiate their own excitatory impulse (have their own inherent heart beat) rather than coming from a nerve
2
Q
Step one of the stimulation of the heart
A
- Sinoatrial node, patch of muscle in the upper right atrium, is the origin of the electrical signals (impulses) - this is called the natural ‘pacemaker’
- Waves of electrical excitation from SAN spread along the muscle cells across the wall of both atria - this causes muscles to contract and push blood into the ventricles (atrial systole)
3
Q
Step two of the stimulation of the heart
A
- Impulses do not travel directly to ventricles (to allow time for atrium to fill) preventing their immediate contraction, because of a ring of non-conducting tissue between the atria and the ventricles
- Impulses reach atrioventricular node (AVN) at the beginning of the septum and there’s a second delay – to allow time for blood to fill the ventricles
- AVN sends impulses down specialised muscle tissue in wall of septum called the Purkynje (aka Purkynje) fibres, arranged into Bundles of His
4
Q
Step three of the stimulation of the heart
A
- Electrical impulse reaches muscle at apex of heart then travels up wall of ventricles in Purkyne fibres causing contraction from the base, upwards - ventricular systole
- Blood is pumped through semi-lunar valves (the semi-lunar valve in the aorta is sometimes referred to as the aortic valve)
5
Q
What does the autonomic nervous system consist of?
A
- sympathetic nervous system and parasympathetic nervous system
6
Q
Features of the sympathetic nervous system
A
- stimulates effectors
- speeds up activities
- controls activities in stressful situations eg. Fight or flight
7
Q
Features of parasympathetic nervous system
A
- inhibits effectors
- slows down activity
- controls activities under normal resting conditions
- conserves energy and replenishes body reserves
8
Q
Control by chemoreceptors
A
- increase in muscular/metabolic activity
- carbon dioxide levels increase due to increase in respiration
- ph of blood decreases
- chemical receptors in carotid arteries increase frequency of impulses in medulla
- centre in medulla oblongata that increases heart rate increases frequency of impulses to the Sinoatrial node via the sympathetic nervous system (nervous tissue within the spinal cord)
- Sinoatrial node increases heart rate so heart beats faster
- breathing increases and excess carbon dioxide is exhaled
- blood ph returns to normal
- chemical receptors in carotid arteries reduced frequent of impulses to the medulla oblongata which causes parasympathetic to slow heart rate back to normal
9
Q
Control by pressure/baro receptors when blood pressure is higher than normal
A
- baroreceptors increase the frequency of impulses to the medulla
- the centre in the medulla oblongata that decreases heart rate increases frequency of impulses to the Sinoatrial node via parasympathetic nervous system
- Sinoatrial node decreases heart rate and reduces blood pressure
10
Q
Control by pressure/baro receptors when blood pressure is lower than normal
A
- baroreceptors increase frequency of impulses to the medulla
- the centre in the medulla oblongata that increases heart rate increases frequency of impulses to the Sinoatrial node via the sympathetic nervous system
- the Sinoatrial node increases heart rate and blood pressure
11
Q
What is the p wave
A
- impulses spreading across the atria - atrial systole
12
Q
What is the pr interval
A
- time taken for impulses to be conducted from Sinoatrial node to atrioventricular node to ventricles
13
Q
What is the qrs complex
A
- impulses spreading up through ventricles - ventricular systole
14
Q
What is the T wave
A
- recovery of ventricles during diastole
15
Q
What can you detect on an ecg?
A
- arrhythmias (irregular heartbeats)
- myocardial infarction (ST elevation)
- fibrillation (small P waves)
- hypertrophy (deep s waves)
- tachycardia or bradycardia (fast or slow heart rates)
