Muscle [Cardiac] Flashcards
Structure of atrial cells
No t tubules. Contract weakly. Gap junctions.
Structure of ventricular cells
Larger, branched, gap junctions, t tubules.
Pathway of action potentials in the cell
Initiated in the right atria in the sino-atrial node. Spreads through the atria via conducting cells (purkinje) to the ventricles.
How is Ca2+ able to stay in the cell to keep AP longer?
lCa produces Ca influx into cell through slow channels. This triggers SR channels to open. The increased calcium is balanced by the Na/Ca exchanger. Cell is kept depolarised bc not many K+ channels are open
What does the Na/Ca exchanger pump in and out and what is the effect of this?
Pumps in 3Na+
Pumps out 1 Ca2+
What is the AP like if triggered during the refractory period?
Smaller as wouldn’t get much blood therefore tension.
Timing of AP and contraction skeletal vs cardiac
Skeletal: AP during absolute refractory period then nothing during relative.
Cardiac: AP and contraction finish at the same time and start at the same but. But are just different shapes.
LTCC
L-type voltage gated ca2+ channel (lCa) in t-tubule.
Can initiate contraction with this.
What is the difference between skeletal and cardiac muscle in terms of troponin?
Cardiac: troponin has only one calcium specific site.
Skeletal: has two
Is the troponin in cardiac muscle more or less saturated than skeletal and why?
Not fully saturated with calcium due to the calcium transient (curve?) being a lower amplitude.
What type of pump is the Na/Ca exchanger? Like how is it stimulated?
Voltage-gated. Stimulated by repolarisation phase.
2 ways to get rid of Ca2+
SR ATPase
Sarcolemma Na/Ca exchanger
What are pacemaker cells? where are they found?
They are found in SA node of right atria. Reflects tension developed during contraction.
Parasympathetic nerve
Vagous nerve. decrease heart rate by releasing ACh. Slows rate of discharge of SA cells. takes longer to reach threshold.
Sympathetic nerve
Increase HR by releasing NA which increases the rate of depolarisation.