- Cardiac responses to physical activity
- The cardiac impulse
- The dynamic action of the heart is that of a dual-action pump in that both sides of the heart contract simultaneously, even though the functions of the two sides are different.
- Cardiac contractions are initiated by an electrical impulse the originates from the pacemaker or sinoatrial node. Because the heart generates its own impulses is said to be myogenic.
- The electrical impulse travels down the atrial mycardium until it reaches the atrioventricular node, situated in the wall of the septum. This is followed by the atrial walls contracting (atrial systole).
- The AV node conducts the impulse through the bundle of his to the branched network of purkinje fibres located within the septum and the ventricular walls, causing both ventricles to contract (ventricular systole).
- The cardiac cycle
- The cardiac cycle is a sequence of events that make up one heart beat and lasts for about 0.8 seconds, thus occurring about 75 times per minute.
- The cardiac cycle consists of a period of relaxation of the heart muscle, known as diastole (0.5 seconds) followed by a period of contraction of the heart muscle, known as systole (0.3 seconds).
- During systole the electrical impulse is initiated in a set-timed sequence.
- Cardiac diastole
- During diastole (0.5 seconds), the relaxed heart muscle allows the chambers to fill with blood.
- This occurs with the cuspid valves open, and the semi-lunar valves closed.
- Cardiac systole
- During atrial systole (0.3 seconds), the SA node impulse causes a wave-like contraction over the atria, forcing blood past the the cuspid valves into the ventricles. The semi-lunar valves remain closed.
- In ventricular systole, the impulse reaches the AV node, the cuspid valves close because the fluid pressure (of blood) in the ventricles is greater than the atria, and rises further as the ventricles contract.
- The semi-lunar valves open (since now the fluid pressure in the ventricles is greater than in the main arteries) and blood is pushed out into the pulmonary artery (towards the lungs) and the aorta (around the body).
- The cardiac responses
- -Heart rate is defined as 'the number of beats of the heart per minute (bpm)' -The average resting HR for males is 70bpm, and for females 72bpm. -At rest, the HR for a trained athlete = 60bpm (less than this would be bradycardia), and the HR for an untrained person = 70-90bpm.
- The cardiac impulse
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