Cardiac muscle and electrophysiology

Question 1

What is the sarcolemma?

Answer 1

The cell membrane that encloses the cardiomyocyte

Question 2

The sarcoplasm contains the ____.

Answer 2

Organelles

Question 3

T tubules are like a collecting duct system where the ____ is stored.

Answer 3

Calcium

Question 4

Are T tubules intra- or extracellular?

Answer 4

Extracellular, though they do delve into cells

Question 5

What is the function of intercalated disks?

Answer 5

Hold cardiomyocyte cells together and allows them to communicate in a mechanical sense

Question 6

The sarcomere is the ____ ____ of cardiac muscle

Answer 6

Contractile element

Question 7

The Z line to Z line is the…

Answer 7

Length of a sarcomere

Question 8

What are the two filaments of cardiac muscle?

Answer 8

Actin and myosin

Question 9

True or false: branching is not typical of cardiomyocytes

Answer 9

False

Question 10

True or false: cardiomyocytes typically have only 1 or 2 nuclei

Answer 10

True

Question 11

What are gap junctions?

Answer 11

The electrical or chemical connects between the cells

Question 12

Desmosomes act as an ____ to keep the muscles from ____.

Answer 12

Anchor

Tearing

Question 13

Why are cardiomyocytes resistant to fatigue?

Answer 13

Lots of mitochondria

Question 14

Which is the thin filament?

Answer 14

Actin

Question 15

Do the filaments themselves contract with the muscle?

Answer 15

No, just move between each other

Question 16

Which is the thick filament?

Answer 16

Myosin

Question 17

Troponin is a ____ ____.

Answer 17

Cardiac enzyme

Question 18

Which ion causes contraction?

Answer 18

Calcium

Question 19

What does calcium bind to in cardiomyocyte contraction?

Answer 19

Troponin C

Question 20

What are the two types of cells throughout the myocardium?

Answer 20

Pacemaker cells (also called nodal cells) and cardiomyocytes

Question 21

Where are pacemaker cells found in the heart?

Answer 21

• SA node
• AV node
• Bundle of His
• Perkinje fibres

Question 22

What particular quality do pacemaker cells possess?

Answer 22

Automaticity - they depolarise themselves.

Question 23

Do pacemaker cells have a higher or lower resting membrane potential than cardiomyocytes?

Answer 23

Higher, making it easier to depolarise

Question 24

What is threshold potential?

Answer 24

Minimum voltage required to open the ion channels required to cause depolarisation

Question 25

What occurs in phase 4 of depolarisation?

Answer 25

Cell is at resting membrane potential, K is inside the cell, Na and Ca are outside the cell.

Question 26

What occurs in phase 0 of depolarisation?

Answer 26

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.

Question 27

What occurs in phase 1 of depolarisation?

Answer 27

K channels open and K leaves the cell

Question 28

What occurs in phase 2 of depolarisation?

Answer 28

Ca channels open and Ca starts flowing into the cell, causing a plateau as it counteracts the exiting K

Question 29

What occurs in phase 3 of depolarisation?

Answer 29

Na/K ATPase pump pulls K back into the cell and pushed Na and Ca out in order to return to resting state

Question 30

Summarise the action potential phases

Answer 30

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

Question 31

Describe the absolute refractory period

Answer 31

The time period during which the cell will not respond to further stimulation

Question 32

Describe the relative refractory period

Answer 32

Vulnerable period; some cardiac cells have repolarised and can be stimulated to respond to a stronger than normal stimulus

Question 33

Describe the flow of electricity through the heart

Answer 33

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

Question 34

In a normal heart the SA node fires at a rate of ____ to ____ per minute

Answer 34

60 to 100

Question 35

What is the effect of inotropes?

Answer 35

Increased force of contraction

Question 36

What is an example of an inotrope?

Answer 36

Adrenaline

Question 37

What effect does more adrenaline have on the heart?

Answer 37

More Na and Ca moving into cells, resulting in a faster HR and stronger contraction

Question 38

What effect does more acetylcholine have on the heart?

Answer 38

Less Na and Ca moving into cells, resulting in a slower HR and decreased force of contraction