While evaluating an electrocardiogram (EKG) during a routine physical exam, the nurse notes that the patient's heart rate is 62 beats per minute with a P wave for every QRS complex and that these are occurring in regular intervals. The nurse determines that the rhythm is normal sinus rhythm, indicating that the heartbeats are following the normal electrical conduction route originating in which of the following? 


•Normal sinus rhythm originates in the sinoatrial or SA node. "Sino" means sinus, and "atrial" means from the atria which are the upper heart chambers. The SA node is located in the upper area of the right atrium.

•Electrical impulses in the heart normally originate in the SA node, then travel to the atrioventricular or AV node, then to the Bundle of His, down both bundle branches, and along the Perkinjie fibers, which then stimulate the ventricles to contract.  

•The large size of the ventricles requires more electrical impulse to cause contraction, which is why the Perkinjie fibers spread out along both ventricles. This is similar to how your car requires a larger battery charge than your flashlight.

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