Learning Module 1:
Cardiac Physiology
Clark J. Cotton
What is Your Heart Rate?
•
To take your pulse, place your
fingers on your wrist and count
heart beats.
•
Alternatively, place your fingers
over your neck and count beats.
•
Your pulse is the number of beats
in 15 seconds multiplied by 4.
What is a Heart?
•
The heart is composed of
contractile muscle, similar to our
skeletal muscle.
•
The heart acts as a pump for our
bodies’ blood supply.
– Blood is pumped to the lungs
via the right ventricle to pick
up oxygen.
– Blood is pumped to the tissue
via the left ventricle to
distribute oxygen throughout
the body.
Basic Heart Anatomy
•
Heart consists of 4 chambers
(2 atria & 2 ventricles).
•
Atria are smaller than ventricles,
left ventricle bigger than right
ventricle.
•
Blood flows in the following
order:
1. Right atria
2. Right ventricle
3. Lungs
4. Left atria
5. Left ventricle
6. Rest of Body
What is an Action Potential?
•
Normally, our cells maintain a
membrane potential of -55mV.
•
During an action potential, the
membrane potential quickly
reaches +5mV for a short time.
•
The large spike in membrane
potential is due to an influx of
positive Na+ and Ca2+ ions.
What Causes a Heart Contraction?
•
There are several areas of the heart that rhythmically fire action potentials
generating a wave of electrical energy. This electrical signal is what causes
the heart muscles to contract.
•
The S-A node depolarizes at the fastest rate and is therefore the
pacemaker for the heart. The rest of the nodes transfer the electrical signal
of the SA-node to the other chambers of the heart, stimulating them to
contract in turn.
Electrocardiograms (ECGs)
•
Because a large number of cells in
the heart rhythmically depolarize,
with each contraction, we can
record the electrical changes on
our body surface.
•
This electrical trace is known as an
electrocardiogram.
Electrocardiogram and Heart Rate
1.
ECG
The SA-node is the first part of
the heart to show electrical
activity.
Heart
Electrocardiogram and Heart Rate
2.
ECG
Shortly after the SA-node fires,
both atria of the heart depolarize
(P-wave) followed closely by
atrial contraction.
Heart
Electrocardiogram and Heart Rate
3.
ECG
There is a brief pause, and then
the AV-node, Bundle of HIS,
and Purkinje fibers fire in
succession (QRS complex).
Heart
Electrocardiogram and Heart Rate
3.
ECG
There is a brief pause, and then
the AV-node, Bundle of HIS,
and Purkinje fibers fire in
succession (QRS complex).
Heart
Electrocardiogram and Heart Rate
3.
ECG
There is a brief pause, and then
the AV-node, Bundle of HIS, and
Purkinje fibers fire in
succession (QRS complex).
Heart
Electrocardiogram and Heart Rate
3.
ECG
There is a brief pause, and then
the AV-node, Bundle of HIS, and
Purkinje fibers fire in succession
(QRS complex).
Heart
Electrocardiogram and Heart Rate
4.
ECG
Following Ventricular
depolarization, the ventricles
contract and repolarization
(T-wave) occurs.
Heart
How Does the Electrical Signal Travel
Throughout the Heart?
•
The electrical signal from
pacemaker cells spreads to nearby
cells via gap junctions.
•
Gap junctions are channels that
are shared by two adjacent cell
membranes.
•
When one heart cell fires an
electrical signal, the signal quickly
spreads to neighboring cells.
Concept Maps
•Concept maps are a great way to organize
complex material in an easy to understand
manner.
•For example, consider the concept of a
farm. To describe a farm, you might use
the following terms:
Farm, Farmer, Banker, Hired
Help, Livestock, Land,
Machinery, Crops, Manure.
•A concept map provides a useful
framework in which to visualize these
terms.
Concept Maps
•Concept maps are a great way to organize
complex material in an easy to understand
manner.
•For example, consider the concept of a
farm. To describe a farm, you might use
the following terms:
Farm, Farmer, Banker, Hired
Help, Livestock, Land,
Machinery, Crops, Manure.
•A concept map provides a useful
framework in which to visualize these
terms.
Cardiac Physiology Concept Map
•Construct a concept map of cardiac
physiology using the following terms:
Atria, Ventricles, gap junctions, action
potentials, p-waves, QRS complex, twave, arteries, veins, systole, diastole,
pacemaker, SA-node, AV-node, Bundle
of HIS, Purkinje fibers,
electrocardiogram.