Cardiovascular system notes

Cardiovascular system notes - Cardiovascular System The...

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Unformatted text preview: Cardiovascular System The cardiovascular system includes the heart and the blood vessels. A functional cardiovascular system is vital for survival, because w/o blood circulation, the tissues lack oxygen and nutrients, and wastes accumulate. Under such conditions, the cells soon begins irreversible change, which quickly leads to death. As blood moves through the system, valves in the heart and veins ensures that blood flows in one direction. The Conduction System of the Heart Cardiac muscle, unlike skeletal muscle, does not require commands from the CNS to contract. Instead, cardiac muscle contractions are triggered by signals originating from within the muscle itself. For this reason, the contractile activity of cardiac muscle is said to be myogenic . (The contractile activity of the skeletal muscle is said to be neurogenic because the initial signal for contraction originates in neurons.) The ability of the heart to generate signals that trigger its contractions on a periodic basis-that is, to generate its own rhythm- is called autorhythmicity . The hearts autorhythmicity is due to the action of a small percentage of muscle cells, called autorythmic cells, that generate little or no contractile force but that are critical to the hearts pumping action because they coordinate and provide rhythm to the heartbeat. There are two types of autorhythmic cells: 1.) pacemaker cells that initiate action potentials and establish the heart rhythm, and 2) conduction fibers that transmit action potentials through the heart in a highly coordinated manner. Together, these cells make up the conduction system of the heart. A-D). An action potential is initiated in the SA node. From the SA node, impulses travel to the AV node by way of internodal pathways-systems of conduction fibers that run through the walls of the atria. As these signals move through the internodal pathways, they also spread through the bulk of the atrial muscle by way of interatrial pathways. The impulse is conducted to cells of the AV node, which transmit action potentials less rapidly than other cells of the conduction system. As a result, the impulse is momentarily delayed by about 0.1 second before moving onward. E) Form the AV node, the impulse travels through the atrioventricular bundle, also known as the bundle of His (pronounced hiss), a compact bundle of muscle fibers located n the interventricular septum. The AV node and bundle of His are the only electrical connection between the atria and the ventricles, which are otherwise separated by the fibrous skeleton. The signal travels only a short distance through the atrioventricular bundle before it splits into left and right bundle branches, which conduct impulses to the left and right ventricles, respectively....
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Cardiovascular system notes - Cardiovascular System The...

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