Setting the Heart’s Tempo
Cardiac Muscle
The heart is Made up of A type of cardiac
muscle known as myogenic muscle:
Cardiac Muscle: Striated muscle that is
branched.
Myogenic muscle: Muscle that is able to
contract without external nerve stimulation
Proof of Myogenic Muscle
• A heart will continue to beat after it is
removed (usually only a few beats)
• A frog’s heart chopped in small pieces and
sprinkled with salt = each piece beats
How does the heart keep its rythum
Sinoatrial (SA node):
- A bundle of specialized nerve and muscle cells
located in the right atrium below the superior
vena cava
How does the heart keep its rythm
Sinoatrial (SA node):
- A bundle of specialized nerve and muscle cells
located in the right atrium below the superior
vena cava
- Acts as a pace maker
- From this group nerve impulses are
transported to other muscle cells by modified
muscle tissue
How does the heart keep its rythm
Atrioventricular (AV node):
- Acts as a conductor
- Sends the impulse along a special nerve track
down the septum between the two ventricles
How does the heart keep its rythm
Atrioventricular (AV node):
- Acts as a conductor
- Sends the impulse along a special nerve track
down the septum between the two ventricles
- This special tract is called the Purkinje fiber
and it continues up to the atrium
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Result of nerve impulses
Nerve impulse moving down Purkinje fibre:
Contracts the heart muscles starting with the
atria then the ventricles.
Monitoring the heart
Electrocardiograph: Measures the electrical
impulses traveling through the heart. This
provides information about
Monitoring the heart
Electrocardiograph: Measures the electrical
impulses traveling through the heart. This
provides information about
- rate and regularity of heartbeats,
- size and position of chambers,
Monitoring the heart
Electrocardiograph: Measures the electrical
impulses traveling through the heart. This
provides information about
- rate and regularity of heartbeats,
- size and position of chambers,
- presence of any damage (dead tissue does not
contract = abnormal wave)
Monitoring the heart
Electrocardiograph: Measures the electrical
impulses traveling through the heart. This
provides information about
- rate and regularity of heartbeats,
- size and position of chambers,
- presence of any damage (dead tissue does not
contract = abnormal wave)
- effects of drugs or devices used to regulate
the heart (pacemaker) and stress tests
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Heart rate
• Increased need for oxygen during exercise =
heart rate increases to get oxygenated blood
to cells
Tachycardia:
Bradycardia:
Heart rate
• Increased need for oxygen during exercise =
heart rate increases to get oxygenated blood
to cells
Tachycardia: Heart rate over 100 beats per
minute
Bradycardia: Heart rate under 60 beats per
minute with other symptoms such as fainting
Heart Sounds
“Lubb-dubb” : They typical heart sound created
by the closing of the heart valves
Lubb = av valves close
Dubb = closing of the semilunar valve
Diastole:
Systole:
Heart Sounds
“Lubb-dubb” : They typical heart sound created
by the closing of the heart valves
Lubb = av valves close
Dubb = closing of the semilunar valve
Diastole: the relaxing of the heart between
contractions
Systole: The contracting of the heart muscles