CVS - Autonomic Nervous System Flashcards
What does the autonomic nervous system exert control over?
Smooth muscle
Exocrine secretion (salivary glands)
Rate and force of contraction in the heart
What are the two divisions of the ANS?
What is the third division sometimes mentioned?
Parasympathetic
Sympathetic
Enteric nervous system - network of neurones surrounding GI tract, normally controlled by sympathetic and parasympathetic fibres
Where is the cell body of the preganglionic neurone located?
And post ganglionic?
CNS
PNS
What is the origin of the sympathetic division?
What segments do the preganglionic neurones arise from?
Where do they synapse with the post ganglionic neurones?
Thoracolumbar origin
- preganglionic in the thoracic spinal cord and lumbar spinal cord
Arise from segments T1 to L2
Most synapse in Paraverterbal chain of ganglia
Some synpase in a number of prevertebral ganglia
** Short preganglionic, long post ganglionic neurones **
What is the origin of the parasympathetic division?
Where do the preganglionic fibres travel?
Where do they synapse with the post ganglionic neurones?
Craniosacral origin
In cranial nerves or sacral outflow
Ganglia - close to target cells
Long pre-ganglionic, short post ganglionic.
What do preganglionic neurones release?
What receptors does it act on?
What type of ion channel do these receptors have?
Acetylcholine
Nicotinic Ach receptors on post ganglionic cell
Integral ion channel - which is permeable to K+ and Na+
What causes an action potential to be fired down the axon?
Influx of Na+ ions, depolarises the cell.
Reaches threshold and action potential fired down the axon
What type of receptors do the post ganglionic neurones of the
a) sympathetic neurones
b) parasympathetic neurones
Have?
What is the exception?
Sympathetic - noradrenergic (noradrenaline as transmitter)
Parasympathetic - cholinergic (Ach as transmitter)
Sweat glands (sympathetic) - post ganglionic release Ach which acts on muscarinic ACh receptors
What cells of the adrenal medulla are like specialised post ganglionic sympathetic neurones?
What do they release? Where does it circulate?
Chromaffin cells
Release adrenaline - which circulates in the blood stream
What is the type of receptors to noradrenaline and adrenaline?
What are their types? And subtypes?
Adrenoreceptors which are G protein coupled receptors
alpha adrenoreceptors = a1-adrenoreceptor, a2-adrenoreceptor
Beta adrenoreceptors = b1-adrenoreceptors, b2-adrenoreceptor
Why do different tissues have different subtypes of receptors?
Allows for diversity of action
Selectivity of drug action
What is a co-transmitter?
Name two types of Co- transmitter
Other transmitters released with noradrenaline and adrenaline at the synpase of the post ganglionic neurone with the effector cells
NPY and ATP
What receptors does ACh act on?
What type of receptors are they?
Is there an integral ion channel?
Muscarinic receptors
G protein coupled receptors (M1, M2, M3)
No integral ion channel
What receptors have an integral ion channel?
And which don’t?
Nicotinic receptors
Muscarinic receptors - G protein coupled receptors DONT.
In the parasympathetic nervous system what receptors are on the post synaptic and effector cells?
Pre ganglionic releases Acetylchloline
Post ganglionic = Has nicotinic receptors on (with integral ion channel)
Effector cells = have Muscarinic receptors (M1, M2, M3) NO integral ion channel
In the sympathetic nervous system what receptors are on the post synaptic and effector cells?
Pre ganglionic releases ACh
Post ganglionic = nicotinic ACh receptors
Effector cell = adrenogenic receptors
What are the functions of the autonomic nervous system?
Regulates physiological functions e.g. BP
SNS and PNS innervate a tissue they often have opposite effects
When is sympathetic activity increased?
When is parasympathetic system more dominant?
Under stress
Under basal conditions
They work together to maintain balance
Is sympathetic drive to different tissues independently regulated?
Yes e.g. Sympathetic activity to the heart can be increased without increasing activity to the GI tract
On some occasions (fight or flight) there can be a more coordinated sympathetic response
What does the autonomic nervous system control in the CVS?
Heart rate
Force of contraction of the heart
Peripheral resistance of blood vessels - controls arterioles constriction and how much resistance there is to the blood flow
What influence is the heart under at rest?
What happens if you denervate the heart (remove all innervation)?
Vagal influence - PNS dominates and keeps HR down
Heart will beat to 100bmp
Where are the preganglionic fibres in the parasympathic input to the heart?
Where do the preganglionic neurones synapse with the post ganglionic neurones?
What do the postganglionic cells release?
Which receptors do they act on?
What are the effects?
Pre ganglionic fibres at 10th cranial nerve vagus
On epicardial surface of at SA and AV node
ACh
M2 receptors
Decrease heart rate and decrease AV node conduction velocity
note - not much effect on force of contraction
Where do the post ganglionic fibres from the sympathetic input to the heart come from?
What do they innervate?
What do they release?
What receptors does it act on?
What are the effects?
Sympathetic trunk
Innervate SA node, AV node and myocardium
Noradrenaline
Acts mainly on Beta 1 adrenoreceptors
Increase heart rate
Increase force of contraction
How do cells in the SA node set the pace of the heart?
What sets the rhythm of the heart?
They steadily depolarise towards the threshold
Slow depolarising pacemaker potential
Turning on of a slow Na+ conductance (If - funny current)
Opening of Ca2+ channels
Action potentials firing in the SA node
What is the sympathetic effect of the ANS on pacemaker potentials?
Mediated by B1 receptors
Gs protein coupled receptors (S=stimuli)
Increase cAMP, active the HCN channels, more channels open, faster the slope back to threshold
Speeds up pacemaker potential
What is the parasympathetic effect of the ANS on pacemaker potentials?
Parasympathetic effect mediated by M2 receptors
Gi (i= inhibitory) protein coupled receptor
Increase K+ conductance, pulls resting potential more negative from threshold so takes longer to get back to threshold.
Decrease cAMP - cAMP will deactive the HCN channels
How does noradrenaline increase force of contraction?
Noradrenaline acting on B1 receptors in myocardium causes an increase in cAMP –> activates PKA
Phosphorylation of Ca2+ channels increases Ca2+ entry during the plateau of the action potential
Increased uptake of Ca2+ in sarcoplasmic recticulum
Increased sensitivity of contractile machinery
What type of innervation do most vessels receive?
What is the exception?
Sympathetic
Some specialised tissue e.g. Erectile tissue has parasympathetic innervation
What types of receptors are in most arteries and veins?
Alpha 1 adrenorecptors
Coronary arteries just from b2 receptors
Skeletal muscle has alpha 1 adrenorecptors and b2 receptor
Some blood vessels have B2 receptors as well as adrenoreceptors
What allows vasodilation to occur?
Vasomotor tone
What receptor does adrenaline have a greater affinity for?
What will happen at high concentrations?
B2 receptors than alpha 1 adrenoreceptors.
It will activate alpha 1 receptors
What effect will adrenaline have on activating b2 receptors?
Vasodilation - increases cAMP –>PKA –>opens K+channels and inhibits MLCK –> relaxation of smooth muscle
What effect will adrenaline have on activating alpha 1 adrenoreceptors?
Vasoconstriction - stimulates IP3 production
Increase in Ca2+ from stores via influx of extracellular calcium binds to calmodulin –> contraction of smooth muscle
What is the role of local metabolites?
What effect do local increases in metabolites have?
Active tissue produces more metabolites e.g. K+, H+, adenosine, incrase PCO2.
Strong vasodilator effect
More important for ensuring adequate perfusion of skeletal and coronary
muscle than activation of B2 receptors
How are changes in the state of the CVS communicated to the brain?
What is their role?
What receptors are found on the high pressure and low pressure side of system?
Via afferent nerves
Alters activity of efferent nerves
Baroreceptors - high pressure side
Atrial receptors - low pressure side
Where are the nerve endings of baroreceptors found?
What are they sensitive to?
Where is the control centre located?
Carotid sinus and aortic arch
Sensitive to stretch
Higher the BP, wider the walls of the artery will stretch, cause more AP to be fired.
Adrenal medulla
What drugs act on the ANS?
Sympathomimetics - alpha adrenoreceptor and beta adrenoreceptor
Adrenorecptors antagonists
Cholinergics - muscarinic agonist and antagonists
What uses do sympathomimetric drugs have on the CVS?
When do you administer adrenaline?
What is dobutamine? When may it be given?
What drug is given for asthma and why?
To restore function in cardiac arrest, along with electric shocks to restart heart
Also administered for anaphylactic shock
B1 agonist - given in cardiogenic shock (pump failure)
Salbutamol - B2 agonist - causes relaxation of bronchiole smooth muscle so you can breathe better
Give an example of a alpha one antagonists and describe how it works?
Give two examples of a beta adrenoreceptor antagonist. What effects does the drug have on the beta 1 and beta 2 receptors?
Prazosin - anti hypertensive. Inhibits noradrenaline action on vascular smooth muscle a1 receptors = vasodilation.
Propranolol - non selective B1/B2 antagonist. Slows heart rate and reduces force of contraction (b1) but also acts on bronchial smooth muscle causing bronchoconstriction (b2)
Atenolol - selective B1 (cardio-selective) - less risk of bronchoconstriction
Name a muscarinic agonist and when it is used.
Name a muscarinic antagonists and when it’s used. When may it be used in examination.
Agonist - pilocarpine, used in treatment of glaucoma - activates constrictor papillae muscle
Antagonist - atropine/tropicamide - increases HR and bronchial dilation - used to dilate pupils for examination.
Where are alpha adrenoreceptor found?
Where are beta adrenoreceptors found?
Smooth muscle
Heart, smooth muscle of airways of lung, adipose and some blood vessels - particularly in skeletal muscle
What is cardiac output the product of?
Heart rate
Stroke volume
What is the principal means by which distribution of flow around the CVS is controlled?
Interplay between the sympathetic vasoconstrictor tone and the action of vasodilator substances
What is the normal resting heart rate?
60bpm
How is the action of the parasympathetic system on heart rate mediated?
How it the action of the sympathetic system on heart rate mediated?
Via acetylcholine acting on M2 muscarinic receptors
Noradrenaline acting on Beta 2 adrenoreceptors
What is the autonomic nervous system important for?
Regulating many physiological functions e.g. Heart rate, BP, body temperature (homeostasis)
Coordinating the body’s response to exercise
Outside of voluntary control
