Organ Systems- Electrical and Mechanical Activity of the Heart- 5 and 6
Cardiac Fibers According to AP > What type of channels are involved in fast/slow fibers?
** In fast fibers > You have Na channels involved ** In slow fibers > You have Ca channels involved ** Na channels open fast so more steep phase 0 and Ca channels open more slowly therefore less steep phase 0 in slow fibers
AV node =
- Similar to SA node but slower - Surrounded by fibrous tissue - Delay in conduciveness (0.1 sec) - Importance - "Gatekeeper" - Atria have time to contract
Cardiac Cycle > Summary of events
- Start will P in the ECG which corresponds to atrial depolarization (atria systole) - Then you have QRS which is ventricular systole (ventricles contract/depolarize) - Lastly you have T which is repolarization of the ventricles - Repolarization of atria is not as big as ventricles therefore not well seen on ECG - Atrial and ventricular systole do not overlap (do not contract at the same time) - However the diastole partially does overlap between atria and ventricle
Important characteristics of the cardiac muscle in terms of electrophysiology
1) Initiation of action potential 2) Duration of action potential 3) Propagation 4) Coordination 5) Modulation 6) Cannot rest!
Two broad types of cardiac muscle cells =
1. Conductile cells 2. Contractile cells
S1 =
1st Heart Sound "LUB"
S2 =
2nd Heart Sound "DUB"
Absolute refractory period =
Absolute refractory period is a time when the cell cannot be excited (purple line above)
Anytime when you talk about a gap between S1 and S2 it is...
Anytime when you talk about a gap between S1 and S2 it is ventricular systole
At the end of diastole, the ____ push a little blood into the ____ and that why you have...
At the end of diastole the atria push a little blood into the ventricles and thats why you have another smaller bump on the graph
Cardiac Cycle > What does not overlap?
Atrial and ventricular systole do not overlap (do not contract at the same time)
Duration of AP- Skeletal vs. Cardiac Muscle
Cardiac muscle has much longer duration of AP then skeletal muscle becuase when cardiac muscle contracts and spreads contraction to neighbouring cells whereas in skeletal muscle it does not. The SA node starts the contraction.
Closure of the valves gives you...
Closure of the valves gives you a sound that you can hear on a stethoscope > ** But their opening does not give a sound
Relations between the electrical event and the actual mechanical contraction > When is there completion of repolarization?
Completion of repolarization approx. coincides with peak force
"Fibrous Cardiac Skeleton" > This organization is important for > Coordinated contraction of myocytes within atria or ventricles > Need for cells that differ regarding their... Conduction velocity
Conduction velocity ** Not referring to blood velocity
Contraction or excitation starts in ____ →____
Contraction or excitation starts in SA node —> info then goes to both artia —> then to AV node which sends excitation to apex of ventricles
Contraction starts from ____ to...
Contraction starts from the apex to push the blood into the aorta and not towards the apex (which will cause the heart to explode)
Depolarization of the atria =
Depolarization of the atria is the P wave
Depolarization of ventricle =
Depolarization of ventricle is the QRS
Relations between the electrical event and the actual mechanical contraction > How long is the duration of the AP?
Duration of action potential approx. parallels duration of contraction
Cardiac Fibers According to AP > What is involved in phase 2 of both?
During the phase 2 in both (plateau phase) there is Ca involved
Cardiac Cycle > Which events come first?
Electrical events slightly precede mechanical events.
Highest conduction velocity is from...
Highest conduction velocity is from purkinji cells —> it sends information quickly so ventricles can contract
Cardiac Cycle > What does partially overlap?
However the diastole partially does overlap between atria and ventricle
If the SA node is not working...
If the SA node is not working and the AV node has to take over then the P wave will overlap the QRS wave, because it will cause simultaneous contraction of artria and ventricle
If the SA node is not working properly then ____ can take over for...
If the SA node is not working properly then AV node can take over for initiating contraction - If that is not working then bundle of His can take over but if SA node is not working then heart is never going to be contracting to the best of its abilities
Initiation of AP- Skeletal vs. Cardiac Muscle
Initiation of action potential (AP) in skeletal muscle occurs from outside with neurnal fiber from motor unit Movement inside the heart starts from within the heart itself and does not need external input, in this case nervous system helps with modulation of contraction
Isovolume contraction means...
Isovolume contraction means that the volume remains the same but the pressure differs (increase or decrease)
Cardiac Cycle > Lastly you have...
Lastly you have T which is repolarization of the ventricles
Which type of layer is going to contract faster?
Layer that is closest to the ventricle is going to contract faster then the layer that is farther away —> endo (inside) vs epicardium (outside)
SA node =
Natural (primary) pacemaker of the heart Spontaneous induced depolarization
"Fibrous Cardiac Skeleton" > This organization is important for > Coordinated contraction of myocytes within atria or ventricles > Need for cells that differ regarding their...
Need for cells (fibers) that differ regarding their: - Resting state (MP) - Action potential (AP) - Refractory periods ** Have longer refractory period then skeletal muscles - Conduction velocity ** Not referring to blood velocity
Need less energy to excite the cell in ____ vs. during...
Need less energy to excite the cell in phase vs during the relative refractory period
2nd highest conduction velocity is from...
Next highest is Bundle of His
Cardiac Fibers According to AP > Phase 1 =
Phase 1 is a temporary repolarization
Cardiac Fibers According to AP > Phase 3 has changes in...
Phase 3 (repolarization) has changes in Ca and Na permeability, phase 1 is a temporary repolarization
Relations between the electrical event and the actual mechanical contraction > Phase 4 coincides with what?
Phase 4 (resting state) coincides with relaxation of muscle (diastole)
Cardiac Fibers According to AP > Phase 2 =
Plateau Phase
Relations between the electrical event and the actual mechanical contraction > When does a rapid depolarization occur?
Rapid depolarization slightly precedes force development
"Fibrous Cardiac Skeleton" > This organization is important for > Coordinated contraction of myocytes within atria or ventricles > Need for cells that differ regarding their... Refractory periods
Refractory periods ** Have longer refractory period then skeletal muscles
Cardiac Fibers According to AP > Phase 3 =
Repolarization
Phase 4 =
Resting State
Which ventricle has less pressure?
Right ventricle has less pressure cause it send blood to the lungs
Is S1 or S2 stronger?
S1 is stronger then S2
SA and AV node is surrounded by...
SA and AV node is surrounded by fibroskeleton of the heart
SA and AV node is surrounded by fibroskeleton of the heart > This allows for...
SA and AV node is surrounded by fibroskeleton of the heart > This allows for a little lag to occur between depolarizations so that the atria can fully contract before the ventricles contract > If the delay does not happen then the valves between the atria and ventricles would close early and the ventricles would not fully be filled with blood
____ are in control of cardiac contraction
SA and AV node, and bundle of His are in control of cardiac contraction
SA node = ____ cells and do what?
SA node are slow cells and intiate activity in the atria
Skeletal muscles can communicate through....
Skeletal muscles can communicate through gap junctions that transmit Ca2+ and cardiac muscles have intercalicated disks that also contain gap junctions, therefore if one cell contracts this excitation signal will spreads until all the cells are contracting
Cardiac Fibers According to AP > ____ initiates the AP
Slow response fibers initiates the AP
Two broad types of cardiac muscle cells > Conductile Cells
Specialized in initiation and propagation of action potential
Cardiac Cycle > Start with...
Start will P in the ECG which corresponds to atrial depolarization (atria systole)
Cardiac Fibers According to AP > Starting point for fast response vs. slow response...
Starting point for fast response is more negative then slow response —> therefore slow response cells are more unstable but this is a good thing becuase the instability helps them initiate the AP
T =
T = Repolarization of the ventricles
Two broad types of cardiac muscle cells > Contractile Cells
The "working" myocardium
____ starts the contraction in cardiac muscle
The SA node starts the contraction.
The action potentials in different regions of the heart have...
The action potentials in different regions of the heart have characteristic features
What coincides with the closure of valves?
The beginning and end of the ventricular systole coincide with the closure of valves.
Cardiac Fibers According to AP > The fast response fibers can stay at ____ until they...
The fast response fibers can stay at the resting potential until they do not have to but the slow response fibers are the ones who wake up by themselevs after they have gone into their resting phase
The relative refractory period =
The relative refractory period is towards the end of depolarization and the cell can be excited but only with a higher level of input
Rhythmical discharge of a sinus nodal fiber > The sinus nodal AP is compared with...
The sinus nodal AP is compared with that of a ventricular muscle fiber
Cardiac Cycle > Start with ____ , then have...
Then you have QRS which is ventricular systole (ventricles contract/depolarize)
There is a small lag between...
There is a small lag between the closure of one set of valves and the opening of the other set. (corresponding to the isovolumetric contraction and relaxation)
Cardiac Fibers According to AP > Under certain condition, ____ response may change to ____ response...
Under certain condition, fast response may change to slow response such as in ischemia or atrial fiberiliation and heart beats irregularily
Ventricular muscle fibers start compared to SA node fiber
Ventricular muscle fibers start are more negative potential then SA node fiber
"Fibrous Cardiac Skeleton" > This organization is important for > Arrangement of...
• Arrangement of left and right bundle branches and Purkinje fibers
"Fibrous Cardiac Skeleton" > This organization is important for > Coordinated contraction of...
• Coordinated contraction of myocytes within atria or ventricles
"Fibrous Cardiac Skeleton" > This organization is important for > Hierarchical Arrangement of centers that could...
• Hierarchical arrangement of centers (SA node, AV node, Bundle of His) that could initiate rhythmic contraction, in terms of - location - pacemaker properties
"Fibrous Cardiac Skeleton" > This organization is important for > Propagation of ____ activity
• Propagation of electrical / mechanical activity in an efficient order / manner
"Fibrous Cardiac Skeleton" > This organization is important for > Structural Stability
• Structural stability - For also not allowing direct communication between cells
"Fibrous Cardiac Skeleton" > This organization is important for: SUMMARY
• Structural stability - For also not allowing direct communication between cells • Hierarchical arrangement of centers (SA node, AV node, Bundle of His) that could initiate rhythmic contraction, in terms of - location - pacemaker properties • Arrangement of left and right bundle branches and Purkinje fibers • Coordinated contraction of myocytes within atria or ventricles • Propagation of electrical / mechanical activity in an efficient order / manner • Timing (allowing little planned delays, e.g. for atria to contract a short time ahead ventricles)
"Fibrous Cardiac Skeleton" > This organization is important for > Timing
• Timing (allowing little planned delays, e.g. for atria to contract a short time ahead ventricles)
