Conduction System
GR 12 B
The Conduction System
A. The cardiac muscle is autorhythmic, meaning it
can contract without nerve impulses or hormones.
B. These specialized cells are called nodes or nodal
cells
1. Nodal cells, or pacemaker cells, are specialized
cells that create an electrical impulse at a regular
interval
2. These cells are connected to each other and to
the conducting network
The Conduction System
Nodal cells are divided into two
groups
a. Sinoatrial node (SA)
i. Located in the wall of
the right atrium, near
the entrance of the
superior vena cava
ii. Generates an
electrical impulse at
approximately 70 to 80
impulses per minute
The Conduction System
b. Atrioventricular node
(AV)
i. A second collection
of pacemaker cells
located at the point
where the atria and
ventricles meet
ii. Cells in AV node
generate an electrical
impulse at a rate of 40
to 60 beats per minute
The Heart Rate
1. The SA node sets the heart rate at rest, many
other factors change heart rate
The Heart Rate
a. Autonomic nervous system
(sympathetic and parasympathetic) has
direct connection to SA and AV nodes and
to the myocardium
i.
Sympathetic division can
release neurotransmitters that
increase heart rate and the
force of contraction
ii. Parasympathetic division can
release a neurotransmitter via the
vagus nerve to decrease heart rate
and the force of contraction
The Heart Rate
Ions, hormones, and body temperature
can alter heart rate
i. Fever increases heart rate due to
an increased metabolic rate
ii.
Epinephrine increases heart
rate
iii.
Altered levels of sodium,
potassium, or calcium (ions)
can alter heart activity
• Low potassium can lead to a
weak heartbeat
• High calcium can prolong heart
muscle contractions to the point
where the heart can stop beating
The Heart Rate
Age, sex, and exercise can all impact heart rate
i. Healthy female heart rate is 72 to 80 bpm
ii. Healthy male heart rate is 64 to 72 bpm
Movement of electrical impulses
1. Movement of electrical impulse in the myocardium is
done by specialized conducting cells
2. The conducting cells distribute the electrical impulse in
such a way that
a. The right and left atria contract together first
b. The right and left ventricles contract together next
i. Ventricular contraction spreads from the apex to
the base of the heart
Movement of electrical impulses
a. Once an electric impulse is
generated at the SA node, it
travels to the AV node
b. Once the charge hits the
AV node, it travels through
the AV bundle, or bundle of
His
c. The impulse travels down
the right and left bundle
branch in the
interventricular septum
Movement of electrical impulses
d. These branches
spread across the inner
surface of both
ventricles
e. The impulse travels
into the Purkinje cells
to carry the impulse to
the contractile muscle
cells of the ventricles
• Watch a video on the conduction system
• Conducting System Of The Heart – YouTube