Autonomic Control Of The CVS Flashcards
What is the ANS important in regulating?
Heart rate
BP
Body temperature
(Homeostasis)
How is the autonomic nervous system divided?
Parasympathetic nervous system
Sympathetic nervous system
(Enteric nervous system = sympathetic and parasympathetic fibres)
How long are the pre-ganglionic neurones and post-ganglionic neurones of sympathetic fibres?
Pre-ganglionic = Short
Post-ganglionic = Long
How long are the Pre-ganglionic and post-ganglionic neurones of the parasympathetic fibres?
Pre-ganglionic = Long
Post-ganglionic = Short
Where do the Preganglionic neurones of the Sympathetic nervous system originate (which part of the spine)?
Thoracic lumbar region (Thoracolumbar)
Where do the Preganglionic neurones of the parasympathetic nervous system originate (which part of the spine)?
Craniosacral origin
Which post-ganglionic neurone is close to the target tissue, sympathetic or parasympathetic?
Parasympathetic post-ganglionic is close to target tissue
What neurotransmitter is released at the end of the pre-ganglionic neurones in both the sympathetic and parasympathetic nervous system?
Acetylcholine (ACh)
What receptors are present on the post-ganglionic axon bodies in both the sympathetic and parasympathetic nervous system?
Nicotinic ACh receptors
nAChRs
How does binding of ACh to nicotinic acetylcholine receptors affect the receptor?
Conformational change opens the ion channel of the receptor
Na+ influx
K+ efflux
What type of receptors are all of the adrenergic (adrenoreceptors)?
G protein coupled receptors
What is the neurotransmitter released from the post-ganglionic neurones acting on the effector cells in the Parasympathetic nervous system?
Acetylcholine (ACh)
What are the receptors present in the parasympathetic nervous system that are on the effector cells following the post-ganglionic neurones?
Muscarinic ACh receptors
NOT NICOTINIC ACh Receptor
How are muscarinic ACh receptors different to Nicotinic ACh receptors?
Are G protein coupled receptors
Don’t have ion channels in the receptor like Nicotinic ACh receptors
How many Alpha adrenoreceptors are there?
2
Alpha 1 adrenoreceptors
Alpha 2 adrenoreceptors
How many Beta adrenoreceptors are there?
3
Beta 1 adrenoreceptors
Beta 2 adrenoreceptors
Beta 3 adrenoreceptors
How many Muscarinic receptors are there?
3
M1
M2
M3
How do the sympathetic and parasympathetic nervous system work to maintain a balance together?
Sympathetic increases under stress
Parasympathetic increases under basal resting conditions
Where are B1 receptors found?
Heart
Where are B2 adrenoreceptors found?
Airways of lungs
How does the Autonomic nervous system control the cardiovascular system?
Controls:
-Heart rate
-Force of heart contraction
-Peripheral resistance of blood vessels
What is responsible for initiating the electrical activity of the heart?
The SAN
NOT the Autonomic Nervous System
What happens to the heart if it is denervated and why?
Beats Faster
Not being parasympathetically stimulated by the Vagus nerve which slows the heart (Vagal influence)
What nerve does the parasympathetic input to the heart come from/ where do the pre-ganglionic fibres come from?
10th (X) cranial nerve
Also called the Vagus nerve
Where are the post-ganglionic cells located that the vagus nerve (parasympathetic input) interacts with at the heart?
SAN
AVN
What receptors does the parasympathetic input to the heart act on and what effects does this have?
M2-receptors (muscarinic ACh receptor)
Decreases heart rate = negative chronotropic effect
Decreases AVN conduction velocity/increases time delay initiated
Where are the post-ganglionic fibres of the sympathetic input to the heart innervating?
SAN
AVN
Myocardium (This is not innervated by parasympathetic input only sympathetic)
What neurotransmitter is released by the post-ganglionic fibres of the sympathetic input to the heart?
Noradrenaline
What receptor does noradrenaline mainly act on in the sympathetic input to the heart?
Beta 1 adrenoreceptors
What does activation of the B1 adrenoreceptors in the heart cause?
Positive chronotropic effect
Positive Inotropic effect
What is meant by +ve chronotropic effect?
Increases heart rate
What is meant by +ve inotropic effect?
Increased force of contraction
So where does the sympathetic input to the heart happen?
What receptors are acted on?
SAN
AVN
Myocardium
Beta-1 adrenoreceptors
Where does parasympathetic input to the heart happen?
What receptors are acted on?
SAN
AVN
Muscarinic-2 receptors
What are baroreceptors?
Where are they found?
Stretch mediated receptors that detect changes in arterial blood pressure
How do action potentials take place in the pacemaker region (SAN) of heart?
Slow depolarisation (slow Na+ conductance due to HCN channels causing FUNNY CURRENT)
UPSTROKE = Fast opening of Ca2+ (Calcium INFLUX)
DOWNSTROKE = Opening of K+ channels (K+ EFFLUX) Ca2+ channels close
How does the sympathetic nervous system affect pacemaker potentials/heart rate?
INCREASES heart rate
It increases the speed threshold for an action potential is reached (faster APs)
How does the parasympathetic nervous system affect pacemaker potentials/heart rate?
Decreases heart rate
It decreases the speed which threshold for an action potential is reached (slower APs)
How does sympathetic activity increase the speed by which threshold for an action potential is reached?
Noradrenaline binds to Beta 1 receptors
Activates the G protein (Gs) which stimulates adenylate cyclase (enzyme)
Increases the amount of cAMP
More cAMP can act on HCN channels producing a steeper FUNNY CURRENT
Threshold therefore reached quicker = faster heart rate
How does parasympathetic activity decrease the speed by which threshold for action potentials are reached slowing heart rate?
ACh binds to M2 receptors
G protein activated (Gi) which inhibits adenylyl cyclase (enzyme)
Less cAMP produced
Less HCN channels stimulated so less Na+ moves in, also increased K+ conductance
Therefore take longer for cell to depolarise to threshold potential since takes longer for Na+ to move in through fewer HCN channels
How does noradrenaline have a positive inotropic effect on the heart?
Binds to Beta-1 receptor
Increases cAMP
cAMP activates PKA (Protein Kinase A)
PKA Phosphorylates Ca2+ channels allowing Ca2+ influx into cell
Influx of Ca2+ causes more Ca2+ to be released from the Sarcoplasmic reticulum
PKA also inhibits Phospholamban which brings Ca2+ back int SR
More Ca2+ in cytoplasm = stronger contraction
Do most vessel only have sympathetic innervation or parasympathetic innervation?
Sympathetic innervation
What receptors do most arteries and veins have?
Alpha 1 adrenoreceptors
What receptors do coronary and skeletal muscle vasculature have?
Alpha 1 + Beta 2
What is Vasomotor tone and why is it important?
The normal amount that the smooth muscle of the blood vessel is contracted at rest
Allows for vasodilation if it relaxes more
Allows for vasoconstriction if it constricts more
How does activation of the alpha 1 (A1) receptor on blood vessels with both A1 and B2 adrenoreceptors affect the blood vessel?
What neurotransmitter activates A1?
Vasoconstriction
Noradrenaline
What neurotransmitter will preferentially bind to B2 adrenoreceptors in blood vessels with both A1 and B2 at physiological concentrations?
Adrenaline
What affect does adrenaline binding to B2 have on a blood vessel?
Vasodilation
What affect does noradrenaline or adrenaline binding to A1 adrenoreceptors have on a blood vessel?
Vasoconstriction
In blood vessels that have both A1 and B2 receptors, at HIGH concentrations of adrenaline, which receptor will the adrenaline bind to?
What effect does this have?
A1
Vasoconstriction
In blood vessels that have both A1 and B2 receptors, which receptor will adrenaline preferentially bind to at normal physiological concentrations and what affect does this have?
B2
Vasodilation
How does Activating B2 adrenoreceptors cause vasodilation of vascular smooth muscle?
G protein stimulates Adenylyl cyclase
More cAMP
PKA activated
PKA Phosphorylates MLCK inhibiting it
So MLC not phosphorylated preventing actin myosin interaction (no contraction)
How does activating A1 adrenoreceptors cause vasoconstriction?
G protein stimulates IP3 (Inositol triphosphate) production
IP3 stimulates SR to release Ca2+
Ca2+ interacts with Calmodulin
Ca2+ - Calmodulin complex activates MLCK
MLCK Phosphorylates MLC allowing myosin head to interact with actin
CONTRACTION
What affect do high amounts of metabolites have on vascular smooth muscle?
Vasodilation
What receptors in the carotid sinus and aortic arch detect increased arterial blood pressure?
Baroreceptors
What happens when Baroreceptors are stretched detecting increased blood pressure?
Fire AP to medulla
Decreased sympathetic stimulation
Vasodilation
Bradycardia
What is the baroreceptor reflex?
Maintains blood pressure over short periods
Compensates for moment to moment changes in arterial BP
What is the problem with the baroreceptor reflex?
With hypertension the baroreceptors re-set to a higher level
What are the 3 categories of drugs that act on the ANS
Sympathomimetics
Adrenoceptor antagonists
Cholinergics
What are sympathomimetic drugs?
Drugs that enhance the nerves of the sympathetic nervous system
Alpha adrenoreceptor agonists
Beta adrenoreceptor agonists
What drug is administered in cardiac arrest and anaphylactic shock?
Adrenaline
When adrenaline is administered in anaphylactic shock or cardiac arrest, which adrenoreceptor is being activated?
Alpha 1 (A1)
Due to higher concentrations of adrenaline compared to normal physiological concentrations
When there is cardiogenic shock/pump failure, DOBUTAMINE is given, what type of drug is this?
B1 agonist
Sympathomimetic drug
What affect does a B1 agonist (dobutamine) have on the heart?
Increased heart rate
Increased strength of contraction
When someone has asthma they are often treated with SALBUTAMOL, what type of drug is this?
B2 agonist
Sympathomimetic
How does the B2 agonist salbutamol help treat asthma?
Vasodilation of the smooth muscle
Increased cAMP
Inc PKA
MLCK inhibited (K+ influx no Ca2+)
Muscle relaxes
What is an example of an alpha adrenoreceptor antagonist?
Prazosin
What affect does an alpha 1 (A1) antagonist have on the body?
Meachanism of action of Prazosin
Prevents noradrenaline binding to smooth muscle A1 receptors
Prevents constriction so vasodilation happens
What is a B-adrenoreceptor antagonist that is specifc to B1 receptor?
Atenolol
What affect does the B1 selective adrenoreceptor antagonist Atenolol have on the body?
Affects the heart
Prevents noradrenaline binding to B1
Slows heart rate
Reduces force of contraction
Propranolol is a non selective B1/B2 receptor antagonist, what affect will this have on the body?
Slows heart
Reduces force of heart contraction
Bronchial smooth muscle contraction (bronchoconstriction)
Prevents noradrenaline binding to the B receptors
What are cholinergics?
Muscarinic receptor agonists and antagonists
How can I remember where the beta adrenoreceptors are found?
B1 in heart (only have 1 heart)
B2 in lungs and (have 2 lungs)
Where are alpha adrenoreceptors found?
Blood vessels
What happens to blood vessels when there is:
Increased noradrenaline?
Decreased noradrenaline?
What receptor is being activated more or less?
Increased noradrenaline = Vasoconstriction (increased activation of A1)
Decreased noradrenaline = Vasodilation (Decreased activation of A1)
