The cardiac skeleton

Components

• Fibrous rings surround the atrioventricular canals and the origins of the aorta and pulmonary trunk.
• Membranous inter-ventricular septum

Functions

• Attachment to the valves
• Insertion for the cardiac muscle fibres.

• Consists of specialized cardiac muscle fibres
  
  
• Initiate the normal heart beat
  
  
• coordinate the contractions of the heart chambers.
  
  
• Gives the heart its automatic rhythmic beat.
  
  
• It consists of the following components:
  
  a) Sino Atrial Node : In the wall of right atrium: superior end of crista terminalis to the right of superior vena cava opening
  
  b) Atrio ventricular node: Postero-inferior part of intra-atrial septum, superior to opening of coronary sinus
  
  c) Atrio ventricular bundle of HIS : Runs anteriorly to membranous part of inter ventricular septum, lies inferior to septal cusp of tricuspid valve
  
  d) Right and Left bundle branches: Straddle the muscular parts of inter ventricular septum
  
  e) Purkinje fibres

Functioning of the impulse conducting system

• The SA node initiates the impulse, which is rapidly conducted to the cardiac muscle fibres of the atria, causing them to contract.
  
  
• The impulse enters the AV node.
  
  
• It is then transmitted through the AV bundle to
  
  
• Its branches to the papillary muscles, then throughout the walls of the ventricles.

Although the heart has its own intrinsic rythmicity , this is subject to the influence of the autonomic nervous system.