BIOL 115 Lecture Notes - Lecture 15: Heart Valve, Atrioventricular Node, Intercalated Disc
Document Summary
First the atria contract together, then the ventricles, then the heart relaxes. Occurs 70 times per minute on average. There are two audible sounds: lub-dub : lub: from the closure of the av valves, dub: from the closure of the semilunar valves, murmur: a swishing sound between lub and dub from regurgitation of blood (leaky valves) The sa node in the right atrium initiates the heartbeat by sending out an electrical signal; this causes the atria to contract: sa node is called the peacemaker. This impulse reaches the av node, also in the right atrium: av node sends a signal down the av bundle and purkinje fibers; this causes ventricular contraction. These impulses travel through gap junctions in the intercalated disks. The cardiac control center in the brain increases or decreases the heart rate depending on the body"s needs. An electrocardiogram is a record of the heartbeat.
