The Heart
Basic Physiology
composed of striated muscle along with actin and myosin filaments that lay atop
one another
heart is composed of 3 different types of muscle:
1. Atrial
2. Ventricular
3. Excitatory and Conductive
-1 and 2 act similar to skeletal muscle except contraction is much longer
-3 is automatic rythmic excitation via action potential
Intercalated Disks
dark areas of the cardiac muscle
membranes that separate each cardiac muscle from the other
at each membrane another cardiac muscle is fused creating a gap junction
allows ions to move w/ease- when one cell becomes excited, AP spreads
The Heart 1
, 2 types:
1. Atrial Disks- contain the AV Node- allows for atrial contraction before ventricular
contraction
2. Ventricular Disks
AP in Cardiac Muscle
105 mv rise
from about -85 mv to 20 mv during each beat
remains depolarized for .2 seconds before abrupt repolarization
Plateau
1. more prolonged than skeletal muscle bc action potential is highly dependent on
opening of slow calcium-sodium channels
💡 Calcium-Sodium Channels: allow for slow inflow to the interior of the
heart; are slower to open and remain opened longer than fast sodium
The Heart 2
, 2. decreases membrane permeability to potassium bc of excess calcium influx-
causes slow outflux of potassium so it takes longer for membrane to repolarize
💡 There is also fast sodium channels present in the cardiac muscle
💡 The more calcium there is present- the greater the excitation will be
Refractory Period
time where re-excitation of an already excited cardiac muscle cannot happen
.25-.30 seconds for ventricle
much shorter for atrial- .15-.20 seconds
Cardiac Cycle
events from one beat to the next
1. Spontaneous excitation of the Sinus Node in right atrium
2. Travels to AV Node and to left atrium
-allows for blood to be pumped into the ventricles before the strong contraction of
the ventricles
1. Blood from SVC, IVC, coronary sinus are flowing into atria and some blood is
flowing passively down to the ventricle without contraction
-AV valves are open and atrial pressure is greater than ventricular
2. P wave; SA node is fired and depolarization of atria; remaining 20% of blood is
pushed through- reaching end
Diastole and Systole
The Heart 3
Basic Physiology
composed of striated muscle along with actin and myosin filaments that lay atop
one another
heart is composed of 3 different types of muscle:
1. Atrial
2. Ventricular
3. Excitatory and Conductive
-1 and 2 act similar to skeletal muscle except contraction is much longer
-3 is automatic rythmic excitation via action potential
Intercalated Disks
dark areas of the cardiac muscle
membranes that separate each cardiac muscle from the other
at each membrane another cardiac muscle is fused creating a gap junction
allows ions to move w/ease- when one cell becomes excited, AP spreads
The Heart 1
, 2 types:
1. Atrial Disks- contain the AV Node- allows for atrial contraction before ventricular
contraction
2. Ventricular Disks
AP in Cardiac Muscle
105 mv rise
from about -85 mv to 20 mv during each beat
remains depolarized for .2 seconds before abrupt repolarization
Plateau
1. more prolonged than skeletal muscle bc action potential is highly dependent on
opening of slow calcium-sodium channels
💡 Calcium-Sodium Channels: allow for slow inflow to the interior of the
heart; are slower to open and remain opened longer than fast sodium
The Heart 2
, 2. decreases membrane permeability to potassium bc of excess calcium influx-
causes slow outflux of potassium so it takes longer for membrane to repolarize
💡 There is also fast sodium channels present in the cardiac muscle
💡 The more calcium there is present- the greater the excitation will be
Refractory Period
time where re-excitation of an already excited cardiac muscle cannot happen
.25-.30 seconds for ventricle
much shorter for atrial- .15-.20 seconds
Cardiac Cycle
events from one beat to the next
1. Spontaneous excitation of the Sinus Node in right atrium
2. Travels to AV Node and to left atrium
-allows for blood to be pumped into the ventricles before the strong contraction of
the ventricles
1. Blood from SVC, IVC, coronary sinus are flowing into atria and some blood is
flowing passively down to the ventricle without contraction
-AV valves are open and atrial pressure is greater than ventricular
2. P wave; SA node is fired and depolarization of atria; remaining 20% of blood is
pushed through- reaching end
Diastole and Systole
The Heart 3
