cardiac impulse conduction pathway

1. Cardiac impulse conduction
and innervation
ATIK GOEL
ROLL NO 33
07-07-2023

2. SESSION OBJECTIVES
 Pacemakers of heart
 Electrical conduction system of heart
 Time delay in transmission
 Conduction velocities of various conduction fibres
 Innervation of heart

3. Introduction
Cardiac electrophysiology : All processes
involved in activation of heart , action
potential , conduction system and effects of
ANS.

4. Heart has 2 special systems for
1. Cardiac impulse generation - pacemakers
2. Impulse conduction
This allows atria to contract 1/6th second
ahead of
ventricle
and all ventricle to contract simultaneously

5. Pacemaker
 Generally S A node is pacemaker.
 It is having highest rate of firing 70 -80 beats /min.
 If SA node fails : Pacemakers are
Av node
(40-
60Beats/min)
Bundle of
his(about 40
beats/min)
Purkinje fibres
(15-40
beats/min)

6. SA node
 Flattened ellipsoid specialized cardiac muscle
15mm long 3 mm wide 1mm thick.
 Location : Immediately below and lateral to
opening of superior vena cava
 Normal Pacemaker of heart.
 It develops from right side of embryo and
innervated by right vagus

7. Av node
 Shows AV nodal delay of 0.1 sec.
 AV nodal delay has following
significance :
 Preventing excess transmission
of impulses by SA node .
 Gives time for atria to contract
fully before ventricular
depolarisation
 Located near opening of
coronary sinus
 Conducts Impulses from SA node
 Defect in it’s conduction causes
heart blocks

8. Bundle of his and purkinje fibres
BUNDLE OF HIS
Derived from AV nodal cells
They divide into 2 segments and
lies on inter ventricular septum
They are isolated in a canal till
they form purkinje fibres
 PURKINJE FIBRES
They penetrate the
ventricular wall
Their fast conduction
velocity allows ventricle to
contract almost altogether

9. CONDUCTION SYSTEM
OF HEART

10. Pathway of transmission
SA NODE
INTERNODAL
PATHWAY AV NODE
BUNDLE OF
HIS
PURKINJE
FIBRES

12. SA NODE
INTERNODAL
TRACTS
AV NODE
BUNDLE OF HIS
PURKINJE FIBRES

13.  SA NODE
 INTERNODAL TRACTS
 AV NODE
 BUNDLE OF HIS
 PURKINJE FIBRES
Special pathway in arterial wall that
transmit impulse from SA to AV node.
It has 3 parts
Anterior bachman
Middle wenckebach
Posterior thorel
Impulse from sa node can travel
directly to atrial muscle fibres

14. SA NODE
INTERNODAL
TRACTS
AV NODE
BUNDLE OF HIS
PURKINJE FIBRES

15. SA NODE
INTERNODAL
TRACTS
AV NODE
BUNDLE OF HIS
PURKINJE FIBRES

16. SA NODAL PATHWAY
INTERNODAL
TRACTS
AV NODE
BUNDLE OF HIS
PURKINJE FIBRES

19. CONDUCTION RATE
TISSUE CONDUCTION SPEED (m/sec)
SAN 0.05
ATRIAL PATHWAY 1
AVN 0.02-0.05
BUNDLE OF HIS 1
PURKINJE SYSTEM 4
VENTRICULAR SYSTEM 1
CONDUCTION VELOCITY DEPENDS ON 1. Diameter of fibre
2. Number of gap junctions

20. INNERVATION SYSTEM
OF HEART
BY VAGUS AND SYMPATHETIC NERVOUS
SYSTEM

21. VAGUS (Parasympathetic) effects
 Acetylcholine released at vagal endings increases permeability of fibres to k+
ions.
 This causes increased negativity inside the fibers called hyperpolarization
 This makes tissue less excitable
 Membrane potential of SA nodal fibers decreases to -65 to -75 mv from -55 to
-60mv.
 Therefore initial rise of sinus nodal membrane potential caused by Na and Ca
leakage requires more time to reach threshold.
 They are constantly active, producing a rhythm of 60 – 80 beats per minute. If
the vagus nerve was lesioned, the resting heart rate would be around 100
beats per minute.
Summary: acetylcholine binds on to M₂ receptors, which act to decrease the
slope of the pacemaker potential. This leads to a decrease in heart rate
negative chronotropic effect

22. SYMPATHETIC EFFECT
 The sympathetic input into the heart is via the
postganglionic fibres from the sympathetic trunk which
innervate SA node AV NODE and ventricles mainly.
 The postganglionic fibres release noradrenaline, which
acts on B₁ adrenoreceptors to increase the slope of the
pacemaker potential. By increasing permeability to na+
and ca++ ions.
 This increases the heart rate (a positive chronotropic
effect by ca++), as well as the force of contraction
(positive inotropic effect).

23. Thank you