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Lecture 8 Cardiac Electrophysiology Control

Lecture 8 Cardiac Electrophysiology Control - Lecture 8...

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Lecture 8 Cardiac Electrophysiology Control I. Cardiac Muscle Fibers A. General 1. striated 2. high ATP use – develop tension very quickly 3. small (50 – 100 μ long, 10 -20 μ wide) 4. electrically connected by gap junctions called “interclated disks” 5. blend of skeletal and smooth muscle characteristics B. Contractile fibers – 98% of heart Form chambers Generate pressure Striated with all myofilaments 2 types: Conduction velocity (m/s) AP duration (seconds) Contraction duration (seconds) Atrial 0.3 – 0.5 ~0.2 ~0.2 Ventricular 0.3 – 0.5 ~0.3 ~0.3 1. Can’t tetanize cardiac tissue because to get summation/tetanus, need short electrical event that is done so that you can fire another one before a mechanical event is done. In heart, AP duration matches contraction duration, and there is a refractory period on top of it, heart has time to relax and refill 2. Atrial fibers beat faster C. Nodal fibers – don’t contribute to contraction Specialized to start depolarization Very few myofilaments – so doesn’t generate tension! 1. Sinoatrial node (SA node) right atrium 2. Atroventricular node (AV node) next to triscuspid valve Conduction velocity – 0.02 m/s Slow conduction velocity sets up delay between contraction of atria and contraction of ventricle.
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