Cardiac muscle innervation

Question 1

What is meant by myogenic?

Answer 1

Doesn’t require nervous stimulation to contract

Question 2

Where is the SAN?

Answer 2

Right atrium

Question 3

What is the Em in cardiac myocytes during diastole?

Answer 3

-80mv

Question 4

How does excitation spread between adjacent myocytes?

Answer 4

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

Question 5

Length of ventricular AP?

Answer 5

200ms

Question 6

Compare length of ventricular AP and skeletal muscle AP?

Answer 6

Longer in ventricular cell

Question 7

Ca2+ influx from…is necessary for contraction

Answer 7

Extracellular space (unlike in skeletal muscle)

Question 8

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

Answer 8

Optimised in skeletal muscle

Not in cardiac muscle

Question 9

What are 2 important parts of relaxation?

Answer 9

Ca2+ detaches from troponin and remove cytosolic Ca2+

Question 10

How is contraction terminated?

Answer 10

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

Question 11

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

Answer 11

Stiff ventricle and less filling time

Question 12

What does plateau phase prevent?

Answer 12

Tetanus

Question 13

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

Answer 13

Depolarisation spreads along T tubule membrane

Activate L type channel

Ca2+ enters from extracellular space

Question 14

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

Answer 14

Ca2+ in intracellular space between T tubule membrane and SR

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

Question 15

How are channel kinetics responsible for CICR?

Answer 15

RYR open for longer than L type channel

Question 16

Describe what feedback exists for Ca2+ release from SR?

Answer 16

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

Question 17

How does ouabain operate?

Answer 17

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

Question 18

What is the organisation of SR and t-tubules?

Answer 18

One SR associated with T-tubule, called a diad

Question 19

What does raised Ca2+ allow?

Answer 19

Binds to troponin C, cross-bridge cycling

Question 20

What does Starling’s law state?

Answer 20

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

Question 21

What 3 mechanisms regulate contraction of myocardial cells?

Answer 21

Cardiac nerves
Circulating hormones
Pharmacology

Question 22

What 4 things does PKA phosphorylate to increase inotropy?

Answer 22

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)

Question 23

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

Answer 23

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