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Electrical excitability of cells > Cardiac muscle innervation > Flashcards

Flashcards in Cardiac muscle innervation Deck (23)
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1

What is meant by myogenic?

Doesn't require nervous stimulation to contract

2

Where is the SAN?

Right atrium

3

What is the Em in cardiac myocytes during diastole?

-80mv

4

How does excitation spread between adjacent myocytes?

Through GJs, allow movement of ions between cells and depol to flow across cells

5

Length of ventricular AP?

200ms

6

Compare length of ventricular AP and skeletal muscle AP?

Longer in ventricular cell

7

Ca2+ influx from...is necessary for contraction

Extracellular space (unlike in skeletal muscle)

8

In which muscle are cross bridge formation optimised, where is it not the case?

Optimised in skeletal muscle
Not in cardiac muscle

9

What are 2 important parts of relaxation?

Ca2+ detaches from troponin and remove cytosolic Ca2+

10

How is contraction terminated?

Ca2+ removal via SERCA into SR, Ca2+ ATPase ( mitochondria + cell membrane) and NCX

11

What is the physiological consequence of sluggish Ca2+ reuptake into SR?

Stiff ventricle and less filling time

12

What does plateau phase prevent?

Tetanus

13

What happens in ECC (from beginning to L type channel)?

Depolarisation spreads along T tubule membrane

Activate L type channel

Ca2+ enters from extracellular space

14

Describe ECC (from Ca2+ from ECC to end)?

Ca2+ in intracellular space between T tubule membrane and SR

Ca2+ binds RYR2 on SR membrane and activates it - CICR

15

How are channel kinetics responsible for CICR?

RYR open for longer than L type channel

16

Describe what feedback exists for Ca2+ release from SR?

Larger Ca2+ transient inhibits L type channel, increases NCX activity so reduced Ca2+ in SR and next Ca2+ transient smaller

17

How does ouabain operate?

Block Na+K+, limits NCX, more Ca2+ into SR so stronger contraction

18

What is the organisation of SR and t-tubules?

One SR associated with T-tubule, called a diad

19

What does raised Ca2+ allow?

Binds to troponin C, cross-bridge cycling

20

What does Starling's law state?

SV increases In response to more blood in ventricles before contraction (end diastolic volume)

21

What 3 mechanisms regulate contraction of myocardial cells?

Cardiac nerves
Circulating hormones
Pharmacology

22

What 4 things does PKA phosphorylate to increase inotropy?

L type channel: increase open probability

Phosphalamban: increase Ca2+ reuptake and more Ca2+ for next contraction

Delayed rectifier K+ channel: shortens AP duration

TnI: reduces Ca2+ sensitivity of thin filament - relaxation. (Stronger relaxation, stronger contraction)

23

How do less cAMP and PKA from para nerves decrease HR?

less cAMP - less funny current

Less PKA - less K+ activity, slows pacemaker potential decay

Beta/gamma dimer activates IkAch channel - hyperpolarise cells, more difficult to reach threshold