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- Action potential
- The change in electrical potential that occurs between the inside and outside of the cell of a nerve or muscle fibre when it is stimulated.
- Adenosine receptors
- A class of protein whose activation by adenosine leads to a number of important physiological responses. In the heart, these include a slowing of heart ratei and a slowing of the conduction of electrical impulse generated at the sinus node.
- Arrhythmia
- A term given to any abnormal electrical activity in the heart which results in an abnormal heart rhythm and/or rate.
- Asphyxiation
- Smothering – a severe decrease in oxygen concentration in the body, leading to death.
- Atrial fibrillation (AF)
- An abnormal heart rhythm originating in the atria. Control of the heart rhythm is taken away from the sinus node pacemaker by electrical events in other areas of the atria, resulting in rapid, unsynchronised and irregular atrial stimulations. There is no coordinated contraction, and only a proportion of the impulses are conducted through the atrioventricular node, resulting in a variable and often increased ventricular contraction rate.
- Atrial flutter (AFL)
- Supra-ventricular rhythm disorder characterised by a high atrial contraction rate (300/min) which results in a ventricular contraction every third or fourth time.
- Atrioventricular (AV) node
- A small mass of tissue situated in the wall of the right atrium adjacent to the septum between the atria that passes impulses received from the sinus node to the ventricles.
- Atrium, atria
- Upper chambers of the heart that receive blood from the veins and force it into the ventricles below.
- Autonomic nervous system
- The part of the nervous system that regulates involuntary vital functions, including the activity of the cardiac (heart) muscle. The autonomic nervous systemi has two divisions: the sympathetic nervous systemi and the parasympathetic nervous system.
