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Slide 1

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The mammalian heart is special in that the electrical stimulation
necessary for contraction of its muscles originates from within the
heart itself
Within the heart there is a network of specialised cardiac muscle cells
designed for initiating each heart beat and for the rapid and
co-ordinated spread of excitation
This network of specialised cardiac muscle cells is known as
This conduction consists of:
· the Sino-atrial node (known as the SA node or
· the Atrio-ventricular node or AV node
· the Bundle of His
· conduction fibres called Purkinje fibres
As the stimulus for contraction of the heart originates from within
cardiac muscle, the heartbeat is described as being
MYOGENIC…read more

Slide 2

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The origin of the heartbeat is Another node of
from within a specialised patch AV node specialised tissue known
of cardiac muscle tissue, located as the AV node is
in the wall of the right atrium, located in the right
and known as the sino-atrial portion of the septum
node or SA node between the atria
SA node and close to the
AV valves
in wall of
right atrium Bundle of His
with left and right
bundle branches
The left and
right bundle
branches divide
into smaller
The AV node connects branches
with a bundle of large called Purkinje
fibres called the bundle fibres that
of His, which divides into spread
left and right bundle throughout the
branches ventricular muscle…read more

Slide 3

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When the SA node emits spontaneous As the impulses spread
electrical impulses, they spread rapidly across the atria, they
across both atria due to the inter-connecting stimulate a wave of
nature of the cardiac muscle cells contraction within the
atrial walls and
When the electrical atrial systole is
impulses reach the triggered
border between the
atria and ventricles Fibrous Tissue
they are blocked by
a band of non- Impulses are
conducting AV conducted from
fibrous tissue Node AV node along
the bundle of His
In order to reach The bundle fibres
the ventricles, divide into
electrical impulses numerous
must pass through Purkinje fibres
the AV node, which that permeate
slows down the throughout the
speed of electrical ventricular
transmission muscles
This delay, called the AV delay, The spread of
is extremely important as it electrical impulses
allows the atria to complete their throughout the
contraction before the ventricles ventricles triggers
begin to contract ventricular systole…read more


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