CVS - Autonomic Nervous System Flashcards
What areas of the body does the ANS control?
- smooth muscle (vascular and visceral)
- exocrine secretion
- rate and force of contraction of the heart
What are the two divisions of the ANS?
- parasympathetic nervous system (cranio-sacral origin)
- sympathetic nervous system (thoraco-lumbar origin)
Which receptors does the sympathetic nervous system use to increase the rate of contraction in the heart?
Beta-1
Which receptors does the para-sympathetic nervous system use to decrease the heart rate?
Muscarinic (m2)
Which receptors does the sympathetic nervous system use to relax the lungs?
Beta-2
What does the ANS control within the cardiovascular system?
- heart rate
- force of contraction
- peripheral resistance of blood vessels
- amount of venoconstriction
- DOES NOT initiate electrical activity in the heart, if heart is denervated will beat extremely quickly
Where does the parasympathetic input enter the heart?
It synapses with postganglionic cells on the epicardial surface or within walls at SA and AV node
Which neurotransmitter and receptor does the parasympathetic nervous system use in the heart?
Acetylcholine, which acts on m2 receptors
Describe the sympathetic input to the heart
- postganglionic fibres from sympathetic trunk innervate SA and AV node and myocardium
- release noradrenaline
- acts on beta-1 adrenoreceptors
- increases heart rate and force of contraction
Where are baroreceptors found in the heart?
In the arch of the aorta and in the carotid sinus
What effect does the sympathetic nervous system have on the slope of the pacemaker potential?
It increases it, meaning there is less time between action potentials so the heart rate speeds up.
What effect does the parasympathetic nervous system have on the pacemaker potential?
It decreases the slope, meaning that there is more time between action potentials and the heart rate slows
How does noradrenaline increase the force of contraction in the heart?
- it acts on beta-1 receptors in myocardium which causes an increase in cAMP
- this activates PKA
- phosphorylation of Ca2+ channels increases Ca2+ entry during plateau of the action potential
- increased uptake of Ca2+ in SR
- increased sensitivity of contractile machinery to Ca2+
True or false - most vessels have sympathetic innervation and alpha-1 adrenoceptors
True
Some blood vessels have beta-2 receptors as well as alpha-1 receptors. Which would circulating adrenaline bind to more preferentially?
Noradrenaline from the SNS would bind to alpha-1, and circulating adrenaline would bind to beta-2
How does activating beta-2 adrenoceptors cause vasodilation?
Increases cAMP, increases PKA, opens potassium channels and inhibits MLCK which leads to relaxation of smooth muscle
How does activating alpha-1 adrenoceptors cause vasoconstriction?
Stimulates IP3 production, causing an increase in interior [Ca2+] from stores and via influx from outside cell. This leads to contraction of smooth muscle.
What is the role of metabolites in vasodilation?
Active tissue produces more metabolites, eg. H+ which leads to a vasodilator effect in the local area of the increase. This allows adequate perfusion of muscles
Which receptors detect low blood pressure?
Atrial receptors - baroreceptors detect high blood pressure
What happens if raised arterial pressure activates the baroreceptors in the aorta?
Impulse travels via the afferent pathway to the coordinating centre. Impulse travels via efferent pathways to the effectors. Bradycardia and vasodilation counteract the increased mean arterial pressure
Give a weakness of baroreceptors
They can reset to higher levels with persistent increases in blood pressure
Give some samples of cardiovascular uses of sympathomimetics
- administration of adrenaline to restore function in cardiac arrest
- dobutamine (b1 agonist) can be given in cardiogenic shock
- adrenaline given for anaphylactic shock
Give an example of a use of alpha-adrenoceptor antagonists
Can be used as an anti-hypertensive agent
Give an example of a beta-adrenoreceptor antagonist
- propranolol can be used to slow heart rate and reduce force of contraction, but also causes bronchoconstriction
