| Describe the Sinoatrial Node (SA Node) of the cardiac conduction system | Sinoatrial Node (SA Node) - a collection of specialised cells (pacemaker cells) located in the upper wall of the right atrium, which can spontaneously generate electrical impulses. The rate at which these impulses are generated is influenced by the autonomic nervous system |
| Define the role of sympathetic and parasympathetic nervous systems in regards to the SA Node | Sympathetic nervous system – increases firing rate of the SA node, and thus increases heart rate Parasympathetic nervous system – decreases firing rate of the SA node, and thus decreases heart rate. |
| Describe the Atrioventricular Node (AV Node) of the cardiac conduction system | The Atrioventricular Node (AV Node) acts to delay the impulses by approximately 120ms, to ensure the atria have enough time to fully eject blood into the ventricles before ventricular systole. |
| Describe the Atrioventricular Bundle (Bundle of His) of the cardiac conduction system | The Atrioventricular Bundle (Bundle of His) transmits the electrical impulse from the AV node to the Purkinje fibres of the ventricles. |
| Describe the Purkinje Fibres of the cardiac conduction system | Purkinje Fibres are able to rapidly transmit cardiac action potentials from the atrioventricular bundle to the myocardium of the ventricles Rapid conduction allows coordinated ventricular contraction (ventricular systole) and blood is moved from the right and left ventricles to the pulmonary artery and aorta respectively. |
| What is the difference between action potentials of pacemaker and non-pacemaker cells? | Non-pacemaker cells In non-pacemaker cells, calcium influx prolongs the duration of the action potential and produces a characteristic plateau phase. Non-pacemaker action potentials, also called "fast response" action potentials because of their rapid depolarization, are characteristic of atrial and ventricular myocytes. Pacemaker Cells Pacemaker cells generate spontaneous action potentials that are also termed "slow response" action potentials because of their slower rate of depolarization. |
| Describe vagal effects on cardiac electrophysiology | Ach released at nerve endings for binding with muscarinic receptors. Results in: Hyperpolarisation due to K+ leakage and decreased slope of phase 4 due to reduced inwards If and Ca2+ currents. Slows the SA depolarisation rate >>> Slowed HR (negative chronotropy). |
| Describe sympathetic effects on cardiac electrophysiology | Noradrenaline (NA) released at nerve endings. Binds to β1-adrenoreceptors. Increases Ca2+and If currents. Increasedslopeofphase4 in pacemaker cells. Increased SAN depolarization rate >>> Increased HR (Positive chronotropy) |
| Describe control of heart rate in regards to cardiac electrophysiology | Heart rate is controlled by the two branches of the autonomic (involuntary) nervous system. The sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate. The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate. |
