Certain tissues in the heart called pacemaker tissues are responsible for initiating and propagating the heartbeat. The main pacemaker tissues are the sinoatrial node, atrioventricular node, bundle of His, and Purkinje fibers. The sinoatrial node initiates each heartbeat with an electrical impulse that is transmitted via the atrioventricular node and bundle of His to the Purkinje fibers, which rapidly conduct the impulse to the ventricles and cause them to contract. An artificial pacemaker can be used to generate electrical impulses to regulate the heartbeat if the natural pacemaker tissues fail.

1. ANIMAL PHYSIOLOGY
PACE-MAKER TISSUE OF THE HEART
Dr.J.PRAKASH SAHAYA LEON. ,M.Sc.,B.Ed.,M.Phil.,Ph.D.,
ASISTANT PROFESSOR,
DEPARTMENT OF ZOOLOGY
GOVERNMENT ARTS COLLEGE FOR MEN, KRISHNAGIRI

2. PACE-MAKER TISSUE OF THE HEART
 CERTAIN TISSUES IN THE HEART, CONCERNED WITH THE INITIATION
(GENERATION OF IMPULSE ) AND PROPAGATION (CONDUCTION ) OF THE
HEART BEAT, ARE CALLED PACE-MAKER TISSUE.

 THEY ARE :
 1)SINO-ARICULAR NODE (SAN)
 2)ATRIO-VENTRICULAR NODE (AVN)
 3)ATRIO-VENTRICULAR BUNDLE (OR) BUNDLE OF HIS
 4) PURKINJE FIBERS ie.: RAMIFICATION OF BUNDLE OF HIS.

3. Origin and Conduction of Heart Beat
( PACE-MAKER ACTIVITY )
The conducting system includes the following components.
 A) Sinu-auricular node
 a) Auriculo ventricular node
 b) Bundle of His (AV Bundle)
 c) Purkinje fibres

4. A) Sinu-Auricular Node
 SAN is located on the posterior asper of the heart at the
junction of the superior vena cava with right atrium
 It consists of thin , elongated muscle fibers rich in
glycogen. Fusiform in shape with longitudinal striations
these are called p-cells or pacemaker cells.
 The impulse originated from the sinu-auricular node and it
is picked up and propagated by a special system of tissues
present in the heart.

5. B) Auriculo ventricular node (AV node)
 located at the posterior right border of the inter auricular
septum.
 The impulses arising from the sino auricular node is
picked up by the auriculo ventricular node (AV node).
 It functions as a relay station and it transmits the impulses
to other parts of the heart through the bundle of His.
 When the SA node fails to function, it acts as a resume
pace maker as it can also initiate the cardiac impulse.

6. C) Bundle of His
 The bundle of His originates from the AV node as a
bundle of tissue.
 Immediately after its origin it divides into 2 branches.
 These branches run along the inner border of each ventricle
and reach the tip of the ventricle and then runs upwards
along the outer margin of the ventricle.

7. D) Purkinje fibres
 The bundle of His and its branches produce minute
branches called Purkinje fibres on the wall of the
ventricles.
 These fibers are larger and thicker than cardiac muscle
fibers. Diameter is 70-80mm.
 They transmit the impulses very fast.
 This fibers rich in glycogen content.

8.  During a heart beat, the auricles contract first and the
ventricles contract later.
 This is because there is no muscular continuity between the
auricles and the ventricles.
 The auricles receive the impulses directly from the SA
node.
 The impulses reach the AV node about 0.03 seconds after
their origin from the SA node
 So the ventricles always contract after the auricles.

9. ARTIFICIAL PACE-MAKER
 A pulse generator, which contains both the
battery and the intelligent circuits.
 It can be very small
 This device can be connected to a lead which makes
contact with either the atrium or the ventricular
muscle.

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