Autonomic Control Of The CVS Flashcards
What receptor is stimulated in the pupil of the eye by the sympathetic nervous system ?
A1- which causes dilation of the pupils due to contraction of the radial muscle.
Which receptor is stimulated in the pupil of the eye under parasympathetic influence ?
M3- this causes contraction of the pupil of the eye due to contraction of the sphincter muscle
What receptor is stimulated in the airways under sympathetic influence ?
B2- which causes the airways to relax.
What receptors are activated in the airways of the lungs under parasympathetic influence ?
M3- which causes the smooth muscle to contraction.
What receptors are activated in the heart under sympathetic influence ?
B1 which increases the rate and FORCE of contraction.
What receptors are activated in the heart during parasympathetic influence ?
M2- which causes a decrease in the heart rate,
What receptors are activated in the sweat glands under sympathetic influence - for example when we are nervous ?
A1- this causes sweaty palms / armpits when nervous.
M3 receptors are activated for generalised secretions.
Is the sweat gland under parasympathetic control ?
NO
What does the autonomic nervous system control in terms of the CVS?
1) heart rate
2) force of contraction
3) peripheral resistance of blood vessels
Does the autonomic nervous system initiate electrical activity in the heart ?
No
Would the heart rate increase or decrease , when the heart is denervated ?
Increase , this is because usually the is under the influence of the vagus nerve ( parasympathetic influence ) which allows a slower heart rate.
What is the tenth ( X) cranial nerve called ?
Vagus nerve
Outline the parasympathetic input to the heart
- preganglionic fibres of the vagus nerve synapse with the postganglionic cells on the epicardial surface or within the walls of the heart at the SA/AV node.
- the postganglionic cells release ACH.
- the ACH acts on the M2 receptors in the heart which works to decrease heart rate ( negative chronotropic effect ) and decrease AV node conduction velocity.
Outline features of the sympathetic input to the heart
- post ganglionic fibres from the sympathetic drink inner fates the SA node , AV node and mycocardium.
- releases noradrenaline and acts mainly on B1 adrenoreceptors which increases heart rate ( positive chrontropic effect) , and increases force of contraction ( +ve inotropic effect)
Are there any other beta receptors in the heart - other than B1?
B2 and B3 adrenoreceptors are also present in the heart but the main effect is mediated by b1 adrenoreceptors.
How does sympathetic/parasympathetic stimulation of th heart affect action potentials in the SA node ?
- Sympathetic activity increases the steepness of the depolarising slope ( funny current ).
- this is because sympathetic effect mediated by B1 adrenoreceptors which are G protein coupled receptors which increases cAMP. Which speeds up pacemaker potential.
WHEREAS with the parasympathetic activity , it would decrease the steepness of the slope. The effect is mediated by M2 receptors. Which are G protein coupled receptors which increase K+ conductance ( so it is harder to get to threshold ) and decrease CAMP.
How does noradrenaline increase the force of contraction of the heart ?
1) noradrenaline acts on B1 receptors in the myocardium which causes an increase in cAMP. cAMP goes off to activate protein kinase A.
2) protein kinase A in responsible for the phosphorylation of VOCC ( voltage operated calcium channels). Which causes an influx of Ca2+ because this channel is remained open for longer. This influx causes calcium inducer receptors ( eg ryanodine ) on the surface of the SR to activate which causes an increase release of Ca2+.
3) this leads to an increased force of contraction.
Do vessels mainly receive sympathetic or parasympathetic innervation?
Sympathetic innervation except some specialised tissue for example erectile tissue which have parasympathetic innervation.
Most arteries and veins have which type of receptors?
A1- adrenoreceptors but coronary and skeletal muscle vasculature also have B2 receptors.
Under normal psychological conditions where there needs to be a normal level of vascular tone , what hormone is released ?
Noradrenaline
When there is a decreased sympathetic output, what occurs to the vessels ?
- there is a decreased release of noradrenaline which results in vasodilation.
When there is an increased sympathetic output , what occurs to the vessels ?
They vasodilation because there is an increased release of noradrenaline.
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What type of blood vessels also contain b2- adrenoreceptors as well as A1?
Skeletal muscles
Myocardium
Liver
At physiological concentration circulating adrenaline will preferentially bind to which type of receptor in blood vessels ?
B2 adrenoreceptors which would initiate vasodilation.
This is because circulating adrenaline has a higher affinity for b2 adrenoreceptors than a1 receptors.
At higher concentrations of adrenaline * ( eg during fight or flight or exercising) - what receptors would adrenaline bind to ?
A1 receptors which would cause vasoconstriction.
What are the effects of activating B2- adrenoreceptors in the smooth muscle of vessels ?
B2 receptors are G(s) protein coupled receptors.
2) This would increase production of cAMP from ATP. This would result in the activation of protein kinase A.
3) Protein kinase A opens potassium channels and inhibits MLCK ( myosin light chain kinase) which causes relaxation of the vascular smooth muscle as this prevents the interaction between actin and myosin.
Thus vasodilation.
What are the effects of activating A1 adrenoreceptors in the vascular smooth muscle of vessels ?
1) A1 receptors are G(q) protein coupled receptors.
2) once activated , this activated phospholipase C enzymes which hydrolyses PIP2 into IP3 and DAG.
3) IP3 is responsible for the increase of Ca2+ from stores . Which results in contraction of smooth muscle
THIS RESULTS IN VASOCONSTRICTION.
What sort of metabolites do active tissue produce ?
Adenosine
k+
H+
Increase in PCO2
What is the importance of local metabolites increasing ?
They have a strong vasodilator effect - they are more important for ensuring adequate perfusion of skeletal and coronary muscles than activation of B2-receptors .
Where are baroreceptors found ?
1) carotid sinus
2) aortic arch
What do baroreceptors detect ?
Changes in arterial pressure because they are sensitive to stretch.
Outline the baroreceptors reflex when arterial blood pressure is high ?
- Baroreceptors in the carotid sinus or aortic arch would be stretched.
- A signal would then be sent along an afferent pathway to the medulla oblongata ( at the base of the brain). Which acts as a co ordinating centre.
- This would then be signalled along the efferent pathways ( eg the vagus nerve) to effectors such as the heart and vessels.
- This would cause bradychardia and vasodilation to counteract the increased mean arterial pressure.
Is the barorecetor reflex important in maintaining blood pressure over short term or long term ?
Short term
Give an example of a muscarinic antagonist ?
Atropine or tropicamide which increases heart rate , bronchial dilation?
- used to dilate pupils for examinTions in the eye.
Give examples of muscarinic agonists ?
Pilocarpine which is used in treatment for gluacome which activates constrictor pupillae muscles.
Give examples of a-adrenoreceptors antagonists ?
A1-antagonist eg prazosin. Which is used as a hypertensive treatment. As it inhibits noradrenaline action on vascular smooth muscle allowing vasodilation.
Give examples of B-adrenoreceptors antagonists ?
Propranolol which is a non selective B1/B2 antagonist.
- this slows the heart rate and reduced force of contraction (B1) but also acts on bronchial smooth muscle ( bronchoconstriction).
- ATENOLOL. Which is a selective b1 anatagonist which lessens the risk of bronchoconstriction
What are sympathomimetics?
Drugs that mimic the effects of th sympathetic nervous system.
For example a-adrenoreceptors and b-adrenoreceptors agonists
Giv examples of sympathomimetics
Administration of adrenaline to restore function in cardiac arrest.
- B1 agonist - dobutamine may be given in cardiogenic shock
- Adrenaline is administered for anaphylactic shock ( a1- smooth muscle contraction which improves circulation of blood flow ) B1- heart muscle contraction and smooth muscle relaxation (B2).
