This document summarizes the pacemaker tissues of the heart, including the sinoatrial node, atrioventricular node, bundle of His, and Purkinje fibers. It describes the location and function of each tissue in conducting electrical impulses and initiating heartbeats. The sinoatrial node initiates impulses that are conducted through the atrioventricular node and bundle of His before being transmitted to the ventricles via Purkinje fibers. Artificial pacemakers can be used to generate electrical pulses when the heart's natural pacemaker tissues fail.

1. PACE-MAKER TISSUES OF THE
HEART
Dr.J.PRAKASH SAHAYA LEON, M.Sc.,B.Ed.,M.Phil.,Ph.D.,
ASSISTANT PROFESSOR, DEPARTMENT OF ZOOLOGY,
GOVERNMENT ARTS COLLEGE FOR MEN,
KRISHNAGIRI, TAMILNADU, INDIA
(DEPUTED FROM ANNAMALAI UNIVERSITY)

2. PACE-MAKER TISSUES 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) SA NODE
 2) AV NODE
 3) BUNDLE OF HIS
 4) PURKINJE FIBERS

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

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.
Source : Net , University Books, SARAS Publication

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