Flashcards in Autonomic Nervous System Deck (35):
What is a ganglion?
A neuron cluster
Describe the origin of the sympathetic nervous system
Describe the origin of the parasympathetic nervous system
Cranial nerves III, VII, IX, X
Sacral outflow S2-4
Describe the location of ganglia in the sympathetic nervous system
Paravertebral chain which extends further cranially and sacrally than the origin.
If they don't synapse here, go to the prevertebral chain (e.g. coeliac, superior mesenteric or inferior mesenteric ganglia)
Describe the location of ganglia in the parasympathetic nervous system.
Ganglia are very close to or within tissues
Describe the neurotransmitter and receptor used in preganglionic neurons.
Acetylcholine, binds to nicotinic receptors
State the neurotransmitter most commonly used by the sympathetic post ganglionic neurons
State the neurotransmitter most commonly used by parasympathetic post ganglionic neurons
What type of receptor is an adrenergic receptor?
G-protein coupled receptor
What type of receptor is a muscarinic receptor
G-protein coupled receptor
Describe the function of chromaffin cells and state their location.
In the adrenal gland.
Act as preganglionic synapses, releasing adrenaline into the blood stream rather than having an axon.
What type of receptor is a nicotinic receptor?
Ligand gated sodium channel
Describe the role of the ANS in the function of the cardiovascular system
Modulates heart rate and force, and peripheral resistance of blood vessels.
NO role in initiating action potentials in the heart.
What parasympathetic nerve innervates the heart, and where does it synapse?
Synapses on the epicardial surface of the SAN/AVN.
Small amount synapses on the ventricles
Describe how parasympathetic innervation affects heart rate and force.
ACh acts on M2 receptors to decrease AVN conduction and therefore heart rate.
Has minimal effect on the force of contraction due to the small amount of ventricular synapses.
It has a negative chronotrophic effect.
What sympathetic nerve innervates the heart and where does it synapse?
Cardiac accellerator nerve.
Synapses on the SAN, AVN and myocardium.
Describe how sympathetic innervation affects heart rate and force.
Noradrenaline acts on beta-1 adrenoreceptors, giving a positive ionotropic and chronotrophic effect.
Describe how sympathetic innervation affects the SAN.
The beta-1 adrenoceptor is a GPCR-Gαs, which causes cAMP release using adenylate cyclase when activated.
An increase in cAMP activates HCN in the SAN, increasing rate of depolarisation and therefore increasing rate of contraction of the heart.
Describe how parasympathetic innervation affects the SAN
The M2 receptor is a GPCR-Gαi which inhibits adenylate cyclase when activated. Activation of this therefore lowers cAMP and also increases potassium conductance, which inhibits HCN.
This decreases the rate of depolarisation, decreasing rate of contraction of the heart.
Describe how sympathetic innervation affects the ventricles.
Beta-1 adrenoreceptor activation increases cAMP which activates phosphofructokinase A. This phosphorylates calcium channels, opening them during the plateau phase of the action potential. As the local concentration of calcium is increases, this increases opening of CICR channels, uptake of calcium into the SR and sensitivity of the contractile machinery to calcium.
What channel protein is involved in forming the pacemaker (funny) current?
What ion(s) does it conduct
Sodium and potassium
Describe how coronary and skeletal muscle vasculature adrenoreceptors differ from most arteries and veins.
Coronary and skeletal muscle have beta-2 receptors as well as alpha-1 which is seen in all other vasculature.
Describe parasympathetic innervation of vasculature.
There is none.
Describe how sympathetic innervation causes dilation of blood vessels.
Beta 2 receptors are activated.
Gαs increases cAMP and stimulates protein kinase A, which opens potassium channels and inhibits MLCK, relaxing the smooth muscle.
Describe how sympathetic innervation causes constriction of blood vessels.
Alpha-1 receptors activated.
Gαq increases IP3 production which increases calcium influx from stores and causes an influx of extracellular calcium, causing contraction of smooth muscle.
Describe the main process ensuring adequate perfusion of skeletal and coronary muscle.
Active tissue produces a large number of metabolites. A local increase in these causes a strong vasodilator effect.
Where in the brain do the vagus nerve and sympathetic fibres communicate?
Where are baroreceptors found and what is their function?
In the aortic arch and carotid sinus. Check blood pressure (high pressure environment)
What is the function of atrial receptors?
To check the low pressure side of the cardiovascular system.
What nerve sends blood pressure information from the carotid arteries to the brain, and where in the brain does it synapse?
Give an example of sympathomimetics used in the CVS and their function.
Adrenaline - restores function in cardiac arrest, or for anaphylactic shock
Dobutamine - beta-1 agonist for cardiogenic shock
Give an example of a sympathomimentics used outside of the CNS.
Salbutamol - beta-2 agonist to treat asthma
Give an example of an adrenoreceptor antagonist and its function.
Prazosin - alpha-1 antagonist. An antihypertensive agent, inhibiting NA action on vascular smooth muscle receptors, causing vasodilation.
Propanolol - beta-1/2 antagonist which slows heart rate and force of contraction, but also causes bronchoconstriction.
Atenolol - beta-1 antagonist which slows heart rate and force of contraction with minimal bronchoconstriction
Give an example of a cholinergic agonist and its function.
Pilocarpine - muscarinic agonist used to treat glaucoma. Causes constriction of the pupillary muscles, allowing aqueous humour to drain more quickly.