Electrical activation heart Flashcards
Where is the Sinoatrial node sound?
Crista terminalis of right atrium
What generates rhythm of heart (pacemaker)?
Sinoatrial node (SAN)
How is heart activated?
1) Action potential generated
2) Reaches -60mV leads to opening HCN
channels (hyperpolarisation gated cyclic
nucleoside channels)
3) HCN allows Na+ ions move into cell-
depolarisation from -60mV to -40mV
4) Voltage gated Ca2+ channels open- Ca2+
enters
- lead depolarisation cell membrane +20mV
5) +20mV results in opening K+ channels
6) K+ move out cell, loss of +ve charge results
repolarisation
7) Hyperpolarisation threshold reached
- reopens HCN and Na+ moves into cell
This is a cycle, no need activation
What increases/decreases HR?
Catecholamine- increases
- faster repolarisation
- reach threshold faster
- HR increased
Acetylcholine- decreases
- slows opening HCN
Draw graph show pacemaker action potential?
How does action potential spread?
Exit SAN- spread cells through gap junctions- connexins
Activate other myocytes- Na+ depolarise adj cells
What is the pathway of heart conduction?
1) SA Node
2) AV Node
3) Bundle of His
4) R/L Bundle branches
5) Purkinje Fibres
Label?
Outline process myocardial action potential?
Cardiac myocyte polarised, no HCN channels Activation of myocardium results:
1) Resting potential -90mV
2) Depolarisation cell- reach threshold -70mV 3) Leads Na gated fast channels opening
- Na+ enters the cells, depolarises +20mV
4) K+ channels open
- K+ leaves cell -15mV
5) Voltage gated Ca+2 channels open
- Ca+2 move in
- counters K channels
- result plateau for 200msec
6) Entry Ca+2 into cell cause contraction
myocyte
7) Ca+2 closes, K+ channel opens leads
repolarisation
8) Reaches resting potential -90mV
What 4 steps in myocardial action potential?
What ion responsible?
Draw graph cardiac myocyte action potential (label)
What occurs when calcium enters cardiac myocytes?
Cardiac myocytes have T-tubules
Entry Calcium
Filaments contract- actin-myosin coupled movement
Function of SAN?
Determine HR
60-100 bpm
What is normal HR?
60-100 BPM
What is resting membrane potential?
-60mV
Hyperpolarisation results HCN opening
Calcium enter
Depolarisation cell
Function AVN?
Exit electrical impulse from atria to ventricle
Slow impulse 100-200msec
Allows atria contract and ventricles to fill
Why is there a slow down in impulse?
Allow atria to contract and ventricles fill
Function of his-purkinje system?
Allow rapid electrical conduction into ventricles
Bundle his- large fibres, gap junctions
Rapid spread conduction in ventricles
Effect sympathetic input on HR?
Increases HR (positive chronotropic)
Increase force contraction (positive inotropic)
Increase CO 200%
What controls sympathetic input?
Adrenaline and Noradrenaline
Type 1 beta adrenoreceptors
Increased adenyl cyclase and cAMP
Effect parasympathetic input on HR?
Decrease HR (by 30-40bmp)- negative chrontropic
Decrease force contraction- negative inotropic
Decrease CO (50%)
What is parasympathetic input controlled by?
Acetylcholine- M2 receptors inhibit adenyl
cyclase
- less cAMP
How is there a difference in activation between myocardial and skeletal?
Myocardial- activated adjacent cell
Skeletal- activated nervous system
In what activation is there a plateau phase? Why?
Myocardial- Ca channels open
- maintain plateau phase
- allow refractory period
- allow heart fill
Skeletal- no plateau
- rapid entry Na
- repolarised K+
- no plateau- tetany- spasm occur
