L4.3.1: Intrinsic Conduction System

• INTRINSIC CONDUCTION SYSTEM

  ● “Nodal System”

  ● Cardiac muscle contracts spontaneously and independently of nerve impulses

  ● Spontaneous contractions occur regularly and continuously

  ○ Atrial cells beat 60 times per minute

  ○ Ventricular cells beat 20-40 times per minute

  ● Sets the heart rhythm
• INTRINSIC CONDUCTION SYSTEM

  ● Composed of special nervous tissues; a crossover between muscle and nervous tissue

  ● Ensures unidirectional depolarization of heart muscles (atria to ventricles)

  ● Enforces a heart rate of 75 beats per minute

  ● HEART RATE CONDITIONS

  ○ Tachycardia — rapid heart rate; over 100 bpm

  ○ Bradycardia — slow heart rate; less than 60 bpm
• How does the intrinsic conduction system work?

  [1] The sinoatrial (SA) node (often called the pacemaker) starts each heartbeat

  [2] Impulse spreads through the atria to the atrioventricular (AV) node

  [3] Atria contract

  [4] At the AV node, the impulse is delayed briefly
• How does the intrinsic conduction system work?

  [5] Impulse travels through the AV bundle (bundle of His), bundle branches, and Purkinje fibers

  [6] Impulse on the Purkinje fibers stimulate muscle fibers and

  ventricular walls or myocardium resulting in a “wringing” contraction that begins at the heart apex towards the atria [7] Ventricles contract; blood is ejected from the heart