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The electrical conduction system is set up so that the heart can contract in a sequential regulated function. The SA node depolarizes, setting off a wave of contractions through the atrial tissues. Eventually the wave of depolarization reaches the AV node, which ******s conduction for a fraction of a second. This is enough time to let the atria properly contract and expel blood into the ventricles. After the depolarizing current passes through the AV node, it is rapidly conducted through the bundle of His system, then through to the purkinje fibers.
The bundle of his and purkinje fibers conduct current more rapidly than the surrounding ventricular myocardia. The fibers rapidly conduct current through the interventricular septum to the distal regions of the heart, allowing for a fast, concerted contractile response
SA Node --> AV Node --> Bundle of His --> Purkinje Fibers
Heart Rate is governed mainly by the Autonomic Nervous System.
Copied from wikipedia:
The SA node is richly innervated by parasympathetic nervous system fibers (CN X: Vagus Nerve) and by sympathetic nervous system fibers (T1-4, Spinal Nerves). This makes the SA node susceptible to autonomic influences.
Heart Rate is governed mainly by the Autonomic Nervous System.
Copied from wikipedia:
The SA node is richly innervated by parasympathetic nervous system fibers (CN X: Vagus Nerve) and by sympathetic nervous system fibers (T1-4, Spinal Nerves). This makes the SA node susceptible to autonomic influences.
- Stimulation of the vagus nerves (the parasympathetic fibers) causes a decrease in the SA node rate (thereby decreasing the heart rate). Parasympathetic fibers cannot change the force of contraction, however, because they only innervate the SA node and AV node (which control heart rate only).
- Stimulation via sympathetic fibers causes an increase in the SA node rate (thereby increasing the heart rate and force of contraction). Sympathetic fibers can increase the force of contraction because in addition to innervating the SA and AV nodes, they innervate the atria and ventricles themselves.
Sinoatrial Node (SA) is a region in the upper wall of the right atrium that includes autorhythmic cells. These cells can generate action potentials without the need to be stimulated. Once generated, this action potential causes the contraction of the two atria. Next, this electrical signal is passed on to the Atrioventricular Node (AV), a region located between the right atrium and the right ventricle. The signal will then travel down the Bundle of Hiss, which will branch off to give rise to the Purkinje Fibers. The purkinje fibers distributed the signal throughout the area covering the two ventricles. Once the signal arrives at this region, the two ventricles contract. This explains the delay between the contraction of the two atria and that of the two ventricles.
http://www.youtube.com/watch?v=te_SY3MeWys&feature=related
http://www.youtube.com/watch?v=pLixs5BAsRo&feature=related
http://www.youtube.com/watch?v=te_SY3MeWys&feature=related
http://www.youtube.com/watch?v=pLixs5BAsRo&feature=related