Cardiac muscle innervation Flashcards
What is meant by myogenic?
Doesn’t require nervous stimulation to contract
Where is the SAN?
Right atrium
What is the Em in cardiac myocytes during diastole?
-80mv
How does excitation spread between adjacent myocytes?
Through GJs, allow movement of ions between cells and depol to flow across cells
Length of ventricular AP?
200ms
Compare length of ventricular AP and skeletal muscle AP?
Longer in ventricular cell
Ca2+ influx from…is necessary for contraction
Extracellular space (unlike in skeletal muscle)
In which muscle are cross bridge formation optimised, where is it not the case?
Optimised in skeletal muscle
Not in cardiac muscle
What are 2 important parts of relaxation?
Ca2+ detaches from troponin and remove cytosolic Ca2+
How is contraction terminated?
Ca2+ removal via SERCA into SR, Ca2+ ATPase ( mitochondria + cell membrane) and NCX
What is the physiological consequence of sluggish Ca2+ reuptake into SR?
Stiff ventricle and less filling time
What does plateau phase prevent?
Tetanus
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
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
How are channel kinetics responsible for CICR?
RYR open for longer than L type channel
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
How does ouabain operate?
Block Na+K+, limits NCX, more Ca2+ into SR so stronger contraction
What is the organisation of SR and t-tubules?
One SR associated with T-tubule, called a diad
What does raised Ca2+ allow?
Binds to troponin C, cross-bridge cycling
What does Starling’s law state?
SV increases In response to more blood in ventricles before contraction (end diastolic volume)
What 3 mechanisms regulate contraction of myocardial cells?
Cardiac nerves
Circulating hormones
Pharmacology
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)
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
