KINESIOL 1YY3 Lecture Notes - Lecture 4: Pacemaker Potential, Qt Interval, Purkinje Fibers
2 Feb 2016
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Document Summary
Specialized cardiac muscle cells - in the av node, sa node, av bundles. Resting membrane potential is not -80 it is -60. They have sodium leak channels in greater abundance. Sodium leaks back to the cell - once it"s enough to reach threshold the voltage gated calcium channels open to cause the action potential (depolarization phase) Sodium is still leaking - re-establishing the membrane potential. It reaches threshold much faster than other fibers. Av node it takes a bit longer - fires at a slower rate - 60-70 beats per minute. Sa node is the fastest - fires before the av node even starts to fire - fires at a faster rate - Purkinje fibers - very slow - 25-30 beats per minute. Absolute refractory period - happens when we have depolarization, plateau and part way into the repolarization. Relative refractory period - a lot of action potentials releasing in a row not allowing the heart to fully** contract.
