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Questions and Answers
What is the threshold membrane potential required to fire an action potential?
What is the threshold membrane potential required to fire an action potential?
Which ion is responsible for the repolarisation of the membrane during phase 3 of the action potential?
Which ion is responsible for the repolarisation of the membrane during phase 3 of the action potential?
What is the primary function of HCN channels in the pacemaker potential?
What is the primary function of HCN channels in the pacemaker potential?
What is the effect of parasympathetic activity on the heart rate?
What is the effect of parasympathetic activity on the heart rate?
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What is the shape of the action potential in the sinoatrial node?
What is the shape of the action potential in the sinoatrial node?
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What is the intrinsic heart rate of the sinoatrial node when all autonomic inputs are blocked?
What is the intrinsic heart rate of the sinoatrial node when all autonomic inputs are blocked?
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What type of receptors are activated by noradrenaline in the sympathetic nervous system?
What type of receptors are activated by noradrenaline in the sympathetic nervous system?
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What is the primary function of voltage-gated calcium channels during phase 0 of the action potential?
What is the primary function of voltage-gated calcium channels during phase 0 of the action potential?
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What is the primary location of cardiac pacemaker cells?
What is the primary location of cardiac pacemaker cells?
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What is the term for the slow depolarisation of pacemaker cells towards the membrane potential threshold?
What is the term for the slow depolarisation of pacemaker cells towards the membrane potential threshold?
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What type of channels allow Na+ entry into pacemaker cells, enabling slow depolarisation?
What type of channels allow Na+ entry into pacemaker cells, enabling slow depolarisation?
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What is the significance of the pacemaker cells with the fastest pacing rate?
What is the significance of the pacemaker cells with the fastest pacing rate?
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What is the term for the ability of cells to generate their own action potentials?
What is the term for the ability of cells to generate their own action potentials?
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What is the phase of the action potential in the SA node where the slow depolarisation of pacemaker cells occurs?
What is the phase of the action potential in the SA node where the slow depolarisation of pacemaker cells occurs?
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What is the difference between the action potential generated by cardiac pacemaker cells and ventricular myocardial cells?
What is the difference between the action potential generated by cardiac pacemaker cells and ventricular myocardial cells?
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What is the term for the ability of the atrioventricular node and Purkinje fibres to generate action potentials?
What is the term for the ability of the atrioventricular node and Purkinje fibres to generate action potentials?
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Study Notes
Cardiac Pacemaker Cells
- Pacemaker cells are mostly found in the sinoatrial node (SAN), which is situated in the upper part of the wall of the right atrium.
- These cells have natural automaticity, meaning they can generate their own action potentials.
- The atrioventricular node (AVN) and the Purkinje fibres also have latent pacemaker cells, but they are normally overridden by the SAN.
Action Potential in Sinoatrial Node
- The action potential in the SA node occurs in three phases: pacemaker potential, depolarisation, and repolarisation.
- Phase 4 (Pacemaker potential): slow depolarisation of pacemaker cells towards the membrane potential threshold, achieved by activation of hyperpolarisation activated cyclic nucleotide gated channels (HCN channels).
- HCN channels allow Na+ entry into the cells, enabling slow depolarisation, and are activated when the membrane potential is lower than -50mV.
- Phase 0 (Depolarisation): voltage-gated calcium channels open, allowing an influx of Ca2+, which produces a faster rate of depolarisation to reach a positive membrane potential.
- HCN channels inactivate, and K+ channels open at the peak of the action potential.
- Phase 3 (Repolarisation): efflux of K+ ions out of the cells, resulting in the repolarisation of the membrane.
Control by the Autonomic Nervous System
- The autonomic nervous system (ANS) alters the slope of the pacemaker potential to alter heart rate.
- Parasympathetic activity lengthens the interval between pacemaker potentials, slowing heart rate, via acetylcholine acting on M2 muscarinic receptors at the SAN.
- Sympathetic activity shortens the interval between impulses, increasing heart rate, via noradrenaline acting on B1 adrenoceptors.
- If all autonomic inputs are blocked, the intrinsic heart rate is about 100 beats per minute.
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Description
Learn about the role of voltage-gated calcium channels in generating action potentials in neurons. Understand how these channels interact with HCN channels to produce a rapid depolarization.
