5. Autonomic Control Flashcards
What 3 things does the autonomic nervous system exert control over?
Smooth muscle
Exocrine secretion
Rate and force of contraction in the heart
What are the two divisions of the autonomic nervous system?
Parasympathetic
Sympathetic
What happens where parasympathetic and sympathetic divisions both innervates a tissue?
Have opposite effects
Where in the body are sympathetic alpha1 NA receptors found?
Pupil of the eye - dilation
Sweat glands - for localised secretion
Vasculature - for contraction/relaxation depending on what arteriole bed
Where in the body are beta1 sympathetic NA receptors found?
Heart - increase force and rate of contraction
Where in the body are beta2 sympathetic NA receptors found?
Airways of lungs - relaxation
Coronary and skeletal muscle vasculature - contraction/relaxation
Where in the body are PARASYMPATHETIC M3 ACh receptors found?
Pupil of the eye - contraction
Airways of the lungs - contraction
Where in the body are parasympathetic M2 ACh receptors found?
Heart - decrease rate
Where in the body are SYMPATHETIC M3 ACh receptors found?
Sweat glands - generalised secretion
What nerve supplies the parasympathetic input to the heart?
Preganglionic - Vagus nerve (10th X cranial)
Which nerve fibres supply the sympathetic input to the heart?
Postgangionic from the sympathetic trunk
Where is the synapse of the preganglionic parasympathetic fibres with the postganglionic fibres in the heart?
Epicardial surface or within walls of heart at SA and AV node
Where do the postganglionic fibres of the sympathetic input to the heat innervate?
SA node, AV node, myocardium
What is the name for the way in which the cells in the sinoatrial node steadily depolarise towards threshold?
Pacemaker potential
How does noradrenaline increase the force of contraction?
NA acting on beta1 receptors in myocardium, increase in cAMP, activates PKA. Leads to:
Phosphorylation of Ca2+ channels, so increased Ca2+ entry in plateau of AP.
Increased uptake of Ca2+ in SR.
Increased sensitivity of contractile machinery to Ca2+.
What type of innervation do most vessels receive? What do they release?
Sympathetic, so NA
What does vasomotor tone allow for?
Vasodilation to occur
What happens on increased sympathetic output to alpha1 adrenoceptor?
Vasculature - vasoconstriction
What type of receptors does circulating adrenaline have a higher affinity for?
Beta2 adrenoceptors
What affect does activating beta2 adrenoceptors have on vasculature?
Vasodilation (eg in heart etc so under stress want more blood to reach heart muscle)
What molecular effects does activating beta2 adrenoceptors in vasculature have?
Increases cAMP, PKA, opens K+ channels, inhibits MLCK (myosin light-chain kinase which is only present in vascular smooth muscle), leading to relaxation of smooth muscle
What molecular affects does activating alpha1 adrenoceptors have in vasculature?
Stimulates IP3 production
Increases Ca2+ conc in the cell from stores and via influx of extracellular Ca2+, resulting in smooth muscle contraction
Give 2 examples of metabolises, and what effect does increases in local metabolites have?
Increased PCO2, H+
Strong vasodilator effect
What are metabolites more important than in ensuring adequate perfusion of skeletal and coronary muscle?
Activation of beta2-receptors
What is the baroreceptor reflex important for?
Maintaining BP over short term
What can happen to baroreceptors with persistent increases in blood pressure?
They can reset to higher levels
Where are nerve endings of the baroreceptors found?
Carotid sinus and aortic arch
What are sympathomimetics?
Drugs which mimic the sympathetic nervous system
Give 2 cardiovascular uses of sympathomimetics
Adrenaline - restore function in cardiac arrest or anaphylactic shock
Dobutamine - beta1 agonist given in cardiogenic shock (pump failure)
When would you use an alpha-adrenoreceptor antagonist as an anti-hypertensive agent?
In resistant hypertension
Give 2 examples of beta-adrenoreceptor antagonists and when they are used?
Propranolol - slows HR and reduced force of contraction. But non selective beta1/beta2 antagonist so also acts on bronchial smooth muscle causing bronchoconstriction.
Atenolol - selective beta1
What are the two types of cholinergic drugs which can be used clinically? Give an example of each
Muscarinic agonists - eg pilocarpine for treatment of glaucoma
Muscarinic antagonists - eg atropine which increases HR, bronchial dilation and used to dilate pupils for examination of the eye
