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The heart is myogenic - it is able to beat on its own even after the organism that posessed the heart has died, if placed in well oxygenated Ringer's solution at 37 degrees Celsius. The heart controls the heartbeat electrically, as follows:
* The heartbeat originates at the sinoatrial node (SAN) which is made up of diffusely orientated cardiac fibres and nerve endings from the Autonomic Nervous system (ANS). The SAN initiates the heartbeat, but the rate at which the heart beats can be altered by stimulation from the ANS (the vagus nerve slows heart rate whilst the sympathetic nerve increases heart rate). * The cells of the SAN maintain a differential ionic gradient of -90mV across their membranes. When Sodium ions diffuse into the cells, it leads to depolarisation, and a wave of excitation is spread across the cells of the SAN and is transmitted across the atria at a rate of 1m/s. The atria contract simulataneously. * There is a septum of non-conduction tissue between the atria and the ventricles. This prevents the wave of excitation from spreading directly from the atria to the ventricles. * Instead, the wave of excitation has to travel through a small area of conductive tissue between the atria and ventricles known as the Atrio-ventricular node (AVN).
* This takes longer - around 0.1-0.15 seconds for the wave of excitation to be spread from atria and ventricles, and it means that there is enough time for atrial systole to be completed before ventricular systole occurs. (N.B systole means contraction). * The wave of excitation then travels along the Purkynje fibres which transmit the wave of excitation down the septum of the heart, to the apex, and then spreads upwards. As a result the ventricles contrct simulataneously. * Once the heart has started to contract it is unable to respond to any other stimulus until it has started to relax - it is said to be in the refractory period. * Where there is lack of coordination in the contraction of heart tissue, fibrillation is said to occur - the heart does not contract and relax as a whole - instead it simply 'flutters' and is unable to pump oxygenated blood around the body effectively. Fibrillation can be reversed by using defibrillators to give an electric shock to the heart which makes the heart contract as a whole again.
What else can I help you with?
An electrocardiogram is a recording of electrical changes occurring in the myocardium during what?
Cardiac cycle
What is one complete heartbeat called?
The cardiac cycle.
How does the P wave the qrs complex and t wave relate to the electrical and mechanical evemts of the cardiac cycle?
its related to the dialysis
What is the importance of cardiac cycle?
The importance of cardiac cycle is to sustain human life.
What happens during the T wave of the cardiac cycle?
During the T wave of the cardiac cycle, the ventricles of the heart repolarize, meaning they reset their electrical charge in preparation for the next heartbeat. This phase represents the relaxation and recovery of the heart muscle after contraction.
Is the p wave part of the cardiac cycle?
Yes - On an ECG the P wave is the first wave of the cardiac cycle. It represents the Sinoatrial node which is the natural pacemaker of the heart firing and causing the atria to contract in order to fill the ventricles.
What is the graph detecting the electrical changes in the heart as it beats?
An electrocardiogram is a graphical recording of the cardiac cycle produced by an electrocardiograph monitoring heart beats.
What is a complete cycle of a heart contraction and relaxation called?
Cardiac cycle, which is made up of atrial and ventricular systole and diastole.
What is cardiac depolarization?
Cardiac depolarization refers to the process by which the heart's cardiac muscle cells undergo a change in electrical charge, leading to the initiation of a heartbeat. This occurs when sodium ions rush into the cells, causing the interior to become more positively charged. This electrical event triggers the contraction of heart muscle fibers, allowing the heart to pump blood effectively. Depolarization is a crucial part of the cardiac cycle, ensuring coordinated heart function.
When do the AV valve close during the cardiac cycle?
AV valves close during the systole phase of the cardiac cycle.
What is a cardiac cycle?
Cardiac cyccle is the term referring to all of the events related to the flow of blood that occur from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is the heart rate.
How is the cardiac cycle timing regulated?
The cardiac cycle timing is primarily regulated by the sinoatrial (SA) node, which serves as the heart's natural pacemaker. It generates electrical impulses that initiate each heartbeat, causing the atria to contract. These impulses then travel to the atrioventricular (AV) node, which introduces a slight delay before transmitting signals to the ventricles, ensuring coordinated contractions. Additional factors, such as autonomic nervous system inputs and hormones, can influence heart rate and the timing of the cardiac cycle.
