Cardiovascular Two

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Cardiovascular Two
2012-07-10 09:01:08
Conduction system cardiac muscle electrical contractile activity

Conduction system, cardiac muscle, electrical and contractile activity
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  1. Describe the external nerve supply to the heart?
    •Sympathetic nerves fromĀ 

    • - upper thoracic spinal cord, through sympathetic chain to cardiac nerves
    • - directly to ventricular myocardium
    • - can raise heart rate to 230 bpm

    •Parasympathetic nerves

    • - right vagus nerve to SA node
    • - left vagus nerve to AV node
    • - vagal tone – normally slows heart rate to 70 - 80 bpm
    • - No vagal innervation to ventricular myocardium
  2. Describe the cardiac conduction system?
    •myogenic - heartbeat originates within heart

    •autorhythmic – regular, spontaneous depolarization

    •Sinoatrial (SA) node: pacemaker, modified cells, initiates heartbeat, sets heart rate, located in right atrium

    •fibrous skeleton insulates atria from ventricles

    •AV node: electrical gateway to ventricles in right atrium

    •AV bundle: pathway for signals from AV node into ventricles

    •Right and left bundle branches: divisions of AV bundle that enter interventricular septum

    •Purkinje fibers: upward from apex spread throughout ventricular myocardium to excite cardiomyocytes
  3. Relate the structure of cardiac muscle to its function?
    •Short, branched cells, one central nucleus

    • •Less Sarcoplasmic reticulum, large T-tubules
    • - admit more Ca2+ from ECF

    • •Intercalated discs join myocytes end to end
    • - interdigitating folds - ­ increase surface area
    • - Desmosomes - hold cells together, structural support
    • - electrical junctions - gap junctions allow ions to flow between cardiomyocytes

    •Aerobic respiration, rich in myoglobin and glycogen, large mitochondria

    •Organic fuels: fatty acids, glucose, ketones and lactic acid

    •Fatigue resistant
  4. . Explain how the SA node fires spontaneously and rhythmically?