The Autonomic Nervous System and the CVS Flashcards
What is the ANS important for?
Many physiological functions
Give 4 physiological functions the ANS is responsible for?
Heart rate
Blood pressure
Body temperature
Co-ordinating the body’s response to exercise and stress
What does the ANS exert control over?
Smooth muscle
Exocrine secretion
Rate and force of contraction of heart
What smooth muscle is under ANS control?
Vascular
Visceral
What are the two divisions of the ANS?
Parasymphathetic
Sympathetic
What is the division of the ANS based on?
Anatomical grounds
What is sometimes given as the third division of the ANS?
Enteric
What is the enteric division?
A network of neurones surrounding the GI tract
What is the enteric division normally controlled via?
Sympathetic and parasympathetic fibres
How are the sympathetic and parasympathetic systems organised?
Two neurones are arranged in series.
One starts in the CNS
The two neurones synapse in the peripheral nervous system
Where is the cell body of the preganglionic neurone?
In the CNS
Where is the cell body of the postganglionic neurone?
In the PNS
Give 12 organs innervated by the sympathetic nervous system
Eyes Blood vessels Salivary glands Heart Lungs Adrenal medulla Liver GI tract Bladder Genitalia Blood vessels Sweat glands
Give 9 organs innervated by the parasympathetic nervous system, and what nerve innervates them
Eye- III Lacrimal glands- VII Salivary glands- IX Heart- X Lungs- X Upper GI tract- X Lower GI tract- Nervi erigentes Bladder-Nervi erigentes Genitalia-Nervi erigentes
What is the origin of the sympathetic division?
Thoracolumbar origin
Where do the preganglionic neurones of the sympathetic division arise from?
Segments T1 to L2 (or L3)
Where do most preganglionic neurones in the sympathetic division synapse with postganglionic neurones?
In the paravertebral chain of ganglia
Which sympathetic nerve synapse in a number of prevertebral ganglia?
Coeliac
Superior mesenteric
Inferior mesenteric ganglia
What is the original of parasympathetic nerve?
Craniosacral
What is meant by craniosacral?
Medulla part of brain stem and region of spinal cord
Where do preganglionic parasympathetic nerves travel?
In cranial nerves (III, VII, IX and X), or sacral outflow from S2-S4
Where do parasympathetic preganglionic synapse?
In ganglia close to target tissue
How long are the postganglionic neurones of the parasympathetic division?
Short
What do preganglionic neurones release?
Acetylcholine (ACh)
What is ACh?
An excitatory neurotransmitter
What do ACh do?
Acts on certain nicotinic acetylcholine receptors in postganglionic membranes
What do nicotinic ACh receptors have?
An integral ion channel that permeable to K and Na ions
What does the ion channel in nicotinic ACh receptors cause?
An overwhelming influx of Na ions, causing depolarisation and therefore the firing of an action potential
What are postganglionic sympathetic neurones usually?
Noradrenergic
What is meant by noradrenergic?
Use noradrenaline as a transmitter
What are postganglionic parasympathetic neurones usually?
Cholinergic
What is meant by cholinergic?
Have ACh as a transmitter
What is the exception to sympathetic neurones being noradrenergic?
Sympathetic innervation of sweat glands, where postganglionic neurones release ACh, which acts on muscarinic ACh receptors
What is released from preganglionic neurones in the sympathetic nervous system?
ACh
What happens to ACh once it has been released from the preganglionic neurone?
It is picked up by nicotinic ACh receptors on the postganglionic neurone
Is it always ACh that is released from preganglionic neurones in the SNS?
No
What is released from the postganglionic neurone in the SNS?
Noradrenaline
What happens to noradrenaline one it’s been released from the postganglionic neurone?
It’s picked up by adrenergic receptors on effector cells
Where are chromaffin cels located?
In the adrenal medulla
What are chromaffin cells?
Like specialised postganglionic sympathetic neurones
What do adrenal chromaffin cells do?
Release adrenaline, which circulates in the blood stream as a hormone
What do noradrenaline and adrenaline act on?
Adrenoreceptors called G protein-coupled receptors
Do G protein-coupled have an integral ion channel?
No
How do G protein-coupled receptors differ in their response to adrenaline to noradrenaline?
They respond with different affinities
What are the types of adrenoreceptors?
α and ß
What are the subtypes of α adrenoreceptor?
α1
α2
What are the subtypes of ß adrenoreceptors?
ß1
ß2
Other subtypes exist
What can different tissues have with respect to adrenoreceptors?
Different subtypes
What do different subtypes of adrenoreceptors allow?
Diversity of action
Selectivity of drug action
What are co-transmitters?
Other transmitters that are released with noradrenaline or adrenaline at synapse of post-ganglionic neurone with effect cells
Give two examples of co-transmitters
Neuropeptide Y
ATP
What is released from the preganglionic neurone in the PNS?
ACh
What happens to ACh in the PNS once its been released from the preganglionic neurone?
Its picked up by nicotinic ACh receptor on the postganglionic neurone
What is released from the postganglionic neurone in the PNS?
ACh
What happens once ACh has been released from the postganglionic neurone in the PNS?
It is picked up by muscarinic ACh receptor on effector cell
What kind of receptors are the muscarinic ACh receptors?
G protein-coupled receptors
What subtypes of G protein-coupled receptors are the muscarinic ACh receptors?
M1, M2 and M3
What happens when parasympathetic and sympathetic divisions both innervate a tissue?
They often have a opposite effect
When is sympathetic activity increased?
Under stress
When is parasympathetic activity more dominant?
Under basal conditions
What do the PNS and SNS work together to do?
Maintain balance
Give 5 examples of SNS control
Dilation of pupil of eye Relaxation of lungs Rate and force of contraction of heart increases Localised secretion from sweat glands Generalised secretion from sweat glands
How does the pupil of the eye dilate?
Contraction of radial muscle
What does dilation of the pupil use?
α1 receptor
What does relaxation of the airways of the lungs use?
ß2 receptor
What does the control of rate and force of contraction of the heart use?
ß1 receptor
What does localised secretion from sweat glands use?
α1 receptor
What does generalised secretion from sweat glands use?
M3 receptor
Give 3 examples of things controlled by the PNS
Contraction of the pupil
Contration of the airways
Decrease in the heart rate
How does the pupil contract?
Contraction of sphincter muscle
What does contraction of the pupil use/
M3 receptor
What does contraction of airways in the lungs use?
Usually M3 receptor
What does the PNS use to decrease heart rate?
M2 receptor
Where is sympathetic drive different?
In tissues that are independently regulated
What does the ANS control in the CVS?
Heart rate
Force of contraction of heart
Peripheral resistance of blood vessels
What does the ANS not do in the CVS?
Initiate electrical activity in the heart
What happens to a denervated heart?
It still beats, but at a faster rate
What is the heart under at rest?
Vagal influence
What supplies PNS input into the heart?
10th (X) cranial nerve vagus
Where does the PNS preganglionic fibre inputting to the heart synapse with postganglionic cells?
On the epicardial surface, or within the walls of the heart at the SA and AV node
What is the result of the synapse of the nerve supplying the heart being where it is?
It allows time for the atria to fully contract
What do postganglionic cells of the PNS in the heart nerves release?
ACh
What does ACh act on in the heart?
M2 receptors
What is effect of ACh on the heart?
Decreases heart rate
Decrease AV node conduction velocity
What is the effect of a decrease in heart rate called?
A negative chronotropic effect
Where do the postganglionic fibres for the SNS input into the heart from?
The sympathetic trunk
What does the SNS input into the heart innervate?
SA node, AV node and myocardium
What does SNS activation of the heart cause?
Release of noradrenaline
Where does noradrenaline act in the heart?
Mainly ß1 adrenoreceptors
What is the effect of noradrenaline in the hear?
Positiv chronotropic effect (increases heart rate)
Increases force of contraction
What is the effect of an increase of contraction called?
Positive inotropic effect
Other than ß1, what other adrenoreceptors are present in the heart?
ß2 and ß2, but the main effect is mediated by ß1 receptors
What are the autonomic inputs into the heart?
Medulla oblongata sympathetic motor neurone
Motor vagus nerve (cranial nerve X, PNS)
Sensory vagus nerve
Sensory glossopharyngeal (cranial nerve IX)
Where does the medulla oblongata sympathetic motor neurone go?
From the cardiovascular centre and to the spinal cord
Where does the medulla oblongata sympathetic motor neurone synapse?
The spinal cord
What does themedulla oblongata sympathetic motor neurone synapse with?
The cardiac accelerator nerve in the sympathetic trunk ganglion
What does themedulla oblongata sympathetic motor neurone innervate?
The ventricular myocardium, the AV node, and the SA node
What does the motor vagus nerve innervate?
SA node and AV node
What does the sensory vagus nerve innervate?
Baroreceptors in the arch of the aorta
What does the sensory glossopharyngeal nerve innervate?
Baroreceptors in the carotid sinus
What is the pacemaker of the heart?
Cells in the SAN
What do cells in the SAN do?
Steadily depolarise towards towards threshold- the slow depolarising pacemaker potential
What happens in the pacemaker potential?
There is turning on of a slow Na conductance, called the funny current.
Opening of Ca channels
What sets the rhythm of the heart?
AP firing in the SA node
What effect does sympathetic activity have on the pacemaker potential?
It increases the slope of the pacemaker potential
What is the effect of the SNS on the pacemaker potential mediated by?
ß1 receptors that are G-protein coupled receptors
How do ß1 receptors mediate the effect of the SNS on the pacemaker potential?
They increase cAMP production by stimulating adenyl cyclase.
What effect does parasympathetic activity have on the pacemaker potential?
In decrease the slope
What is the effect of the PNS on the pacemaker potential mediated by?
M2 receptors, which are G protein-coupled receptors
How do M2 receptors mediate their effect on the pacemaker potential?
They increase K conductance, and decrease cAMP by inhibiting adenyl cyclase. K brings the membrane potential down, further from threshold
What effect does noradrenaline have on the force of contraction?
It increases it
How does noradrenaline exert its effect on the force of contraction?
It acts on ß1 receptors in the myocardium, which causes an increase in cAMP, activating protein kinase A
How does the activation of PKA lead to an increased force of contraction?
Phosphorylation of Ca channels open them, increasing Ca entry during the plateau of the AP.
This leads to an increased uptake of Ca into the SR
Leads to increased sensitivity of contractile machinery to Ca
How does increased uptake of Ca into the SR increase the force of contraction?
It increases build up, so there is more Ca to be released
Increased uptake reduced duration of contraction, which is necessary if need the heart to fire at a faster rate
What do most vessels receive?
Sympathetic innervation
What vessels do not receive sympathetic innervation?
Apart from some specialised tissue, such as erectile tissue, which receives parasympathetic tissue
What receptors do most arteries and veins have?
α1 adrenoreceptors
What vessels also have ß2 receptors?
Coronary, liver and skeletal muscle vasculature
How does the affinity of circulating adrenaline differ between α1 and ß2 receptors?
It has a higher affinity for ß2 receptors
What does adrenaline do at physiological concentrations?
Preferentially bind to ß2 adrenoreceptors
What will adrenaline do at higher concentrations?
Activate α1 receptors
What does vasomotor tone allow for?
Vasodilation to occur
What leads to vasodilation?
Decreased sympathetic output
What leads to vasomotor tone?
Normal sympathetic output
What leads to vasoconstriction?
Increased sympathetic output
What effect does activating ß2 receptors have on vessels?
It causes vasodilation
How does activation of ß2 receptors lead to vasodilation?
Causes an increase in cAMP, which activates PKA. This opens K channels, and inhibits MLCK, leading to relaxation of smooth muscele
What effect does activating α1 receptors have on vessels?
Causes vasoconstriction
How does activation of α1 receptors cause vasoconstriction?
It stimulates IP 3 production, causing an increase in intracellular [Ca] from stores and via influx of extracellular calcium, causing contraction of smooth muscle
What does active tissue produce?
More metabolites
Give 4 examples of metabolites produced by active tissues
Adenosine
K+
H+
Increased PCO 2
What effect do local increases in metabolites have?
Strong vasodilator effect
What is the effect of local metabolites on vasodilation important for?
Ensuring adequate perfusion of skeletal and coronary muscle
How are changes in the state of the CVS communicated to the brain?
Via the afferent nerves
What detects changes in the state of the CVS?
Baroreceptors
Atrial receptors
What are baroreceptors involved in?
The high pressure side of the system
What are atrial receptors involved with?
The low pressure side of the system
What are cardiac baroreceptors?
Nerve endings in the carotid sinus and aortic arch that are sensitive to stretch
What stretches the baroreceptors?
Increased arterial pressure
What happens when baroreceptors detect an increase in blood pressure?
It communicates this to the medulla via the afferent pathway.
The coordinating centre of the medulla then sends efferent signals to the heart and the vessels, causing bradycardia and vasodilation
What are the effects of bradycardia and vasodilation?
Counteracts the increased mean arterial pressure
What are the types of drugs that act on the CVS?
Sympathomimetics
Adrenoreceptor antagonists
Cholinergenics
What do sympathomimetics do?
Mimic the action of the sympathetic nervous system
What are the types of sympathomimetics?
α-adrenoreceptor agonists
ß-adrenoreceptor agonist
What are cardiovascular uses of sympathomimetics?
Administration of adrenaline to restore function in cardiac arrest
Dobutamine (ß1 agonist) may be given in cardiogenic shock (pump failure)
Adrenaline administered for anaphylatic shock
Give a non-cardiovascular use for sympathomimetics?
ß2 agonist (salbutomal) used in treatment of asthma
What does salbutamol cause?
Relaxation of bronchiole smooth muscle
What do α-adrenoreceptor antagonists do?
Prevents constriction, therefore dilation, therefore decreases pressure
Why can α-adrenoreceptor antagonists be used as an anti-hypertensive agent?
Because they inhibit NA action on vascular smooth muscle
Give an example of an α1-adrenoreceptor antagonist
Prazosin
Give two examples of ß-adrenoreceptor antagonists
Propranalol
Atenolol
What does propranolol do?
Activates both ß receptors, leading to slowed heart rate and reduced force of contraction (ß1), and acts on bronchial smooth muscle (ß2), leading to bronchoconstriction
Why is propranolol dangerous for use with asthmatics?
It’s not selective
What is atenolol selective do?
ß1, and therefore the heart
What are the types of cholinergics?
Muscarinic agonists
Muscarinic antagonists
What do muscarinic agonists do?
Activate the receptors
Give an example of a muscarinic agonist
Pilocarpine
What is pilocarpine used in?
The treatment of gluacacoma
What is glaucacoma?
Pressure build up in eyeball
Why is pilocarpine used in the treatment of glucacoma?
It activates constrictor pupillae muscle, and so drains and reduces pressure in the eye
Give two examples of muscarinic antagonists
Atropine
Tropicamide
What are muscarinic antagonists used to do?
Increase heart rate
Bronchial dilation- used to dilate pupils for examination of eye
