Lecture 8 -control And Regulation Of Contraction Flashcards
How do you measure strength?
You look at the volume of blood that is ejected
What does the sympathetic nervous system do to the heart?
Increases heart rate as it innervates the nodes of the cell
What do the right sympathetic nerves do?
Innervates the SA node and causes the heart rate to go up
What is a positive chronotropic affect?
Increase in heart rate
What do the left side of the sympathetic nerves do?
Innervates the ventricular muscle which increases the stroke volume (increasing contractility)
What does the parasympathetic nervous system do to the heart?
Decreases heart rate
What does the right side of the parasympathetic nerves do?
Innervates the SA node
What does the left side parasympathetic nerves do?
Innervates the AV node
Can parasympathetic innervation happen in the ventricular muscle?
No only in the nodal tissues
What is a negative chronotropic affect?
Decrease in heart rate
What type of receptors do sympathetic nerve cells have?
Beta 1 receptors
What does sympathetic stimulation do to the regulation of heart rate?
Depolarises the SA node and increases the rate of depolarisation - depolarises the pacemaker of the cell
What happens when the rate of depolarisation increases?
Calcium channels are opened quicker as you have reached the threshold more quickly - more action potentials
What receptors are involved in the parasympathetic regulation of heart rate? And what is the neurotransmitter involved?
M2 muscarinic receptors and acetylcholine
What does parasympathetic stimulation do to the SA node (pacemaker)?
Hyperpolarises the cell and slows the heart rate - membrane potential becomes more negative
What happens when there is a slower depolarisation?
Means it takes longer to reach the threshold so the calcium channels don’t open as quick which decreases the heart rate
What drug blocks the muscarinic receptors?
Atropine
What does Adenylyl cyclase reduce?
Cyclic AMP and produces PKA
What does PKA phosphorylate?
The voltage operating calcium channel (VOC) so ca2+ channels activate quicker
What protein is the muscarinic receptor linked to?
GI protein which inhibits Adenylyl cyclase
What happens to the betagamma subunit in the parasympathetic system?
The betagamma subunit separates from the alpha subunit and the alpha subunit goes off in the membrane and binds and activates the K+ channel
What happens when the K+ channel is activated by the alpha subunit?
The k+ ions leave the cell and the cell repolarises which is why the parasympathetic stimulation hyperpolarises the SA and AV node
Why in the sympathetic response are the intracellular mechanisms more gradual?
Because cAMP levels have to build up, little NE is released during each cardiac cycle
What is the sympathetic response unable to do?
To alter the cardiac behaviour very much within one cardiac cycle
Why is the parasympathetic response rapid?
Because of the direct activation of K+ channels by betagamma subunit (there is no second messenger required)
What are vagus nerves able to do in the parasympathetic response?
Able to exert beat-by-beat control of heart rate - removal of vagus results in increase in heart rate
What stimulation dominates at rest?
The parasympathetic
Extrinsic contraction?
Outside influence on the muscle cells e.g. neurotransmitter or a hormone causes contractility
Intrinsic contraction?
Inherent in the muscle cells, a unique property of cardiac muscles in the cell
Positive inotropic effect?
Increase stroke volume
Positive chronotropic effect?
Increased heart rate
What is an increase in contractility associated with?
An increase in ca2+ ion concentration - have to have more calcium ions as calcium ions trigger contraction
What happens when there is an increased strength of contraction from a build up of pressure?
Stroke volume goes up
How does activation of beta 1 receptors result in more calcium and stronger contraction?
Because PKA phosphorylates the voltage operating calcium channel so you get more trigger ca2+ which means more CICR and stronger contractions
More CICR and stronger contractions =?
Stroke volume increases and contractility increases
What needs to happen for the muscle to relax?
Cytoplasm needs to get ride of ca2+ which occurs by sympathetic stimulation when PKA phosphorylates phospholamban
What happens when phospholamban is phosphorylated?
It speeds up the SERCA pump and you get an increase rate of pumping the ca2+ ions back out the cytoplasm
Where are RYR receptors located?
Underneath the calcium channels
What does maximum sympathies stimulation =
An increase in HR and SV independently
What are class 2 - beta blockers known as?
Negative inotropic
What do class 5 - cardiac glycosides do?
Inhibit the Na+/K+ ATPase pump
What happens when the Na+/K+ATPase pump is inhibited?
Means the intracellular Na+ concentration rises in the cell which depolarises the cell
How does the cell keep the Na+ levels normal when the Na/K+ ATPase pump is inhibited?
The Na/Ca exchanger reverses its led to get rid of the Na+ ions so Ca2+ will enter the cell - triggering a contraction
What are class 5 - cardiac glycosides?
Positive ionotropes
What is the mechanism for intrinsic regulation of stroke volume?
Frank-starling mechanism
What does an increased filling pressure of the atria or the ventricles lead to?
An increase in end diastolic volume (the volume in the atria before contraction)
What does an increase in filling pressure lead to?
An increase in EDV (end diastolic volume) which leads to an increase stretch int eh cardiac muscle which leads to an increase force of contraction
