Cardiac muscle and electrophysiology Flashcards
What is the sarcolemma?
The cell membrane that encloses the cardiomyocyte
The sarcoplasm contains the ____.
Organelles
T tubules are like a collecting duct system where the ____ is stored.
Calcium
Are T tubules intra- or extracellular?
Extracellular, though they do delve into cells
What is the function of intercalated disks?
Hold cardiomyocyte cells together and allows them to communicate in a mechanical sense
The sarcomere is the ____ ____ of cardiac muscle
Contractile element
The Z line to Z line is the…
Length of a sarcomere
What are the two filaments of cardiac muscle?
Actin and myosin
True or false: branching is not typical of cardiomyocytes
False
True or false: cardiomyocytes typically have only 1 or 2 nuclei
True
What are gap junctions?
The electrical or chemical connects between the cells
Desmosomes act as an ____ to keep the muscles from ____.
Anchor
Tearing
Why are cardiomyocytes resistant to fatigue?
Lots of mitochondria
Which is the thin filament?
Actin
Do the filaments themselves contract with the muscle?
No, just move between each other
Which is the thick filament?
Myosin
Troponin is a ____ ____.
Cardiac enzyme
Which ion causes contraction?
Calcium
What does calcium bind to in cardiomyocyte contraction?
Troponin C
What are the two types of cells throughout the myocardium?
Pacemaker cells (also called nodal cells) and cardiomyocytes
Where are pacemaker cells found in the heart?
- SA node
- AV node
- Bundle of His
- Perkinje fibres
What particular quality do pacemaker cells possess?
Automaticity - they depolarise themselves.
Do pacemaker cells have a higher or lower resting membrane potential than cardiomyocytes?
Higher, making it easier to depolarise
What is threshold potential?
Minimum voltage required to open the ion channels required to cause depolarisation
What occurs in phase 4 of depolarisation?
Cell is at resting membrane potential, K is inside the cell, Na and Ca are outside the cell.
What occurs in phase 0 of depolarisation?
Na channels open and Na starts coming into the cell. The cell hits threshold potential and voltage-gated channels open for Na to flood in.
What occurs in phase 1 of depolarisation?
K channels open and K leaves the cell
What occurs in phase 2 of depolarisation?
Ca channels open and Ca starts flowing into the cell, causing a plateau as it counteracts the exiting K
What occurs in phase 3 of depolarisation?
Na/K ATPase pump pulls K back into the cell and pushed Na and Ca out in order to return to resting state
Summarise the action potential phases
4: K+ ions enter cell and Na+ echange via Na/K pump
0: Rapid Na+ influx
1: K+ Cl efflux
2: Ca2 influx and K+ efflux
3: K+ efflux
Describe the absolute refractory period
The time period during which the cell will not respond to further stimulation
Describe the relative refractory period
Vulnerable period; some cardiac cells have repolarised and can be stimulated to respond to a stronger than normal stimulus
Describe the flow of electricity through the heart
SA node in the RA sets the pace -> goes through Bachmann’s bundle to the LA -> moves down intranodal tracks and terminates at AV node (rate limiting step — sets conduction delay) -> comes down to Bundle of His -> splits into L and R bundle branch (L bundle branch has two fascicles, anterior and posterior) -> moves into Purkinje fibres around the ventricles
In a normal heart the SA node fires at a rate of ____ to ____ per minute
60 to 100
What is the effect of inotropes?
Increased force of contraction
What is an example of an inotrope?
Adrenaline
What effect does more adrenaline have on the heart?
More Na and Ca moving into cells, resulting in a faster HR and stronger contraction
What effect does more acetylcholine have on the heart?
Less Na and Ca moving into cells, resulting in a slower HR and decreased force of contraction
