Flashcards in Cardiovascular Medicine - Week 2 Deck (43):
Why is the heart tissue known as a functional syncytium?
Because it contracts as one unit due to the interlocking of its cells via intercalated discs and gap junctions
What anchors cardiac cells together and allows for the passage of ions via gap junctions?
Name the two cardiac muscle cells and what is the difference in their functions?
Contracticle cells do excitation contraction coupling and produce the strength of contraction and conductile/pacemaker cardiomyocytes initiate contraction but do not contribute to the strength of contraction as they have limited contractile proteins.
Where is the SA node located?
In the wall of the right atrium to the right of the superior vena cava
What is the intrinsic firing rate for the SA node in beats / min
70-100 beats per minute
Describe the membrane potential of a conductile cardiomyocytes vs a contractile cardiomyocytes
contractile cardiomyocytes have a stable resting membrane potential. conductile cardiomyocytes have unstable resting potentials known as pacemaker potentials
What connects the sinoatrial node to the av node?
The anterior,middle and posterior internodal pathways.
Why is there a delay between the transmission of the action potential from the sa node to the av node?
To allow time for the atria to empty blood into the ventricles before they contract. The delay occurs because there are less gap junctions and a smaller diameter of the cells.
Where do the Av bundle and the bundle branches travel down to reach the ventricles?
Down the interventricular septum
Name the fibers that project into the ventricular myocardium to conduct the action potential
How does the impulse travel throughout the heart?
From apex to base and endocardium to epicardium
Describe fast response action potentials and which type of Cardiac cells are an example?
Occurs in normal atrial and ventricular contractile mulches and specialised conducting fibers (purkinje fibers).phase 0 is due to a Na+ influx (rapid)
Describe slow response action potentials and which type of Cardiac cells are an example?
Occurs in the SA node and AV node . Phase 0 is due to a Ca++ influx.
Which phase represents the resting membrane stage
Describe phase 0 for a ventricular myocyte
Rapid voltage gates sodium channels open at threshold of -60mV. Depolarisation inactivates sodium channels. Voltage gated calcium and potassium channels start to open at -40mV.
Define chronotropic effect
Effect on a time or rate
Define dromotropic effect
Effecting force of muscle contraction
What effect does the sympathetic nervous system are on heart rate, conductivity and force of contractions?
Positive chronotropic, dromotropic and inotropic effect. Meaning increases rate, conduction and force of contractions. Norepinephrine is released and causes increase in sodium permeability of the cells meaning they reach depolarization faster
How does the parasympathetic nervous system cause decrease in heart rate and conductivity?
It makes the membrane pacemaker potential of the SA node cells more negative by activating acetylcholine sensitive potassium channels and therefore more potassium leaves the cells meaning it is a longer way to depolarise before reaching threshold. Also inhibits production of cAMP and this inhibits calcium cb a els and the funny current (slow sodium channels)
Why is there a plateu in phase 2?
As there is an equal inward and outward calcium and potassium current until the calcium channels deactivate.
What happens in phase 1 for a ventricular myocyte?
Sodium channels inactivate and potassium leaving the cell
What would happen if a heart attack damaged the SA node?
The AV also has the ability to be self excitable however as a much slower rate due to having less gap junctions and a smaller diameter. As this is the case, the AV node can take over however the Persons heart rate will be slower
Name where you would find conductile cells
AV node, SA node, AV Bundle, purkinje fibers
Name where you would find contractile cells
Ventricular muscle and atrial muscle
Are contractile cells also conductile?
Yes as they have gap junctions to propagate the AP
Are conductile cells also contractile?
Not very, only have limited contractile proteins
Is there gap junctions between atrial muscle cells and ventricular muscle cells?
No , only connected by the AV branches
Which direction does Repolarisation go to?
Apex to base BUT epicardium to endocardium
What determines inotropy? (Force of contraction)
Intracellular calcium concentration
What determines chronotropy? ( heart rate)
The SA Node
Where does the calcium source come from in cardiac muscle?
SR And ECF via L type calcium channels
What happens if you decrease slope of phase 0?
Slow conduction velocity
What does a potassium channel inhibitor do?
Delay Repolarisation and increase effective refractory period
What does a calcium channel inhibitor do?
Decreases phase 2 plateau, decreases ap duration, decrease effective refractory period as quicker Repolarisation and negative ionotropic as less calcium for contraction
What is If
The funny current- slow sodium channels
What does fast sodium channel inhibitors do to nodal tissue?
Nothing!! They have slow sodium channels unlike in contractile cells
When you block the slow sodium channels what would happen?
Slow rise of phase 4 and takes longer to reach threshold
Name the gates on a channel
Activation and inactivation gate
What are the ion channel gates like in RMP?
Activation gate gates closed and inactivation gates open-> no ion influz
During threshold what channel gates are open?
Both activation and inactivation gates are open for ion influx
During inactivation what channel gates are open?
Activation gates opened, inactivation gates closed