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35 Cards in this Set
- Front
- Back
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What is the effect of sympathetic nervous system on pacemaker potential?
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Increases slope of pacemaker cell potential -> tachycardia
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What is the effect of parasympathetic nervous system on pacemaker potential?
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Decreases slope of pacemaker potential - brachycardia
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What is tachycardia and brachycardia?
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Tachycardia - increased heart rate
Brachycardia - decreased heart rate |
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Where do preganglionic sympathetic fibres arise from?
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T1-T6
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Where do sympathetic preganglionic fibres synapse?
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Paravertebral sympathetic ganglia
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What is the sympathetic neurotransmitter affecting the heart?
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Noradrenaline on B1 adrenoceptors
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Where do parasympathetic pre-ganglionic fibres arise from?
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Vagal motor nucleus in medulla
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Where do preganglionic parasympathetic fibres synapse?
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Within the heart
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Where do sympathetic fibres innervate the heart?
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Most areas - nodes, atrial and ventricular muscle
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Where do parasympathetic fibres innervate the heart?
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Nodes and atrial muscle
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What is the parasympathetic neurotransmitter in the heart?
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Acetylcholine on M2 muscarinic receptors
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Therefore what does the parasympathetic NS not affect?
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Ventricular contractility
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What are chronotropic effects on the heart?
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Changes in heart rate
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What are inotropic effects on the heart?
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Changes in strength of contraction
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What has the most prominent effect on the heart?
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Vagal tone
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How can atropine change the heart rate?
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Can block M2 receptors, blocks ACh, speeds up heart rate
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What influence does the sympathetic NS have on inotropic/chronotropic effects?
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Increases inotropic and chronotropic effects
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What influence does the parasympathetic NS have on inotropic/chronotropic effects?
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Reduces chronotropic effect
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How does acetylcholine decrease chronotropic effect?
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Leads to hyperpolarising K current out of cell
Harder for potential to reach threshold |
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What is calcium-induced calcium release?
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Calcium entering the cell can lead to calcium release form sarcoplasmic reticulum stores, leading to contraction
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What is the annulus fibrosus?
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The insulating layer between atria and ventricles
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How does the heart act like one big cell?
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The cardiac cells are connected by intercalated discs - action potentials spread through gap junctions
Also desmosomes connect them |
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Name the parts of conduction around the heart
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Sino-atrial node
Special tracts -> atrial muscle contraction Atrio-ventricular node Bundle of His Right & left bundle branch Purkinje fibres -> ventricular muscle contraction |
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Why is atrial excitation complete before ventricular excitation begins? What is the significance of this?
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There is a delay at the AV node (smaller cells, slower conductance)
Allows atria to top up ventricles before exciting ventricles |
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What is an electrocardiogram?
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A record of the potential changes at the skin surface that result from depolarisation and repolarisation of heart muscle
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How does reduction in calcium in the cell occur and what does it cause?
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Reuptake of Ca by sarcoplasmic reticulum or mitochondria
Exchange of Ca for Na driven by Na-K pump |
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Does calcium entering the cell cause a contraction?
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No, calcium entering the cell causes release of calcium from S.R. and mitochondria (CICR) which causes a contraction
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What happens to a cardiac cell when it is depolarising and repolarising?
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A dipole is set up - part of cell positive, part of cell negative
Fully depolarised - whole cell is positive - returns to 0 mark on voltage because there is no dipole (no difference in charge) |
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In an ECG, what does the voltage recorded depend on?
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Orientation of electrodes in relation to dipole
Mass of tissue in which dipole is set up |
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What is the triangle created around the heart in an ECG recording called?
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Einthoven's triangle
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What is represented at each number?
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1 - depolarisation of atria
2 - depolarisation of ventricles 3 - repolarisation of ventricles (repolarisation of atria not an intracellular reading) |
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What can knowing the P-P interval give you?
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Atrial rate
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What can knowing the R-R interval give you?
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Ventricular rate
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What can ECG give you information about?
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Anatomy of the heart - muscle thickness in different regions
Evaluates conduction system Cardiac drug treatment assessment |
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Why is the T wave in the same direction as the R wave?
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Ventricular muscle repolarises before the repolarisation of the bundle branch
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