ANS Innovation Of The Heart Flashcards
What are the 2 branches of the ANS?
Extra point - What is the debatable 3rd branch
Sympathetic and parasympathetic
Extra point - Enteric nervous system.
What is the origin of the sympathetic nerves?
Thoracolumnar origin. Segments T1 to L2/L3
What is the origin of the parasympathetic nerves?
Craniosacral - cranial nerves 3, 7, 9 and 10. Sacral nerves S2 - S4
What is the neurotransmitter in post ganglionic fibres of the sympathetic ANS?
Noradrenaline. Except for sweat glands which have Acetylcholine.
What is the neurotransmitter in the post ganglionic fibres of the parasympathetic ANS?
Acetylcholine
What are Chromaffin cells?
Specialised post ganglionic cells which are found in the adrenal glands.
What do Chromaffin cells do?
Release noradrenaline directly into the blood stream.
What are the 2 types and 4 subtypes of adrenoreceptors?
Alpha - 1 and 2
Beta - 1 and 2
Why do tissues have different subtypes of adrenoreceptors?
It allows diversity of action.
Can be exploited with selectivity of drugs for desired effect
What are adrenoreceptors ?
G protein coupled receptors with no ion channels. They receive adrenaline/noradrenaline.
Which branch of the ANS increases under stressful situations?
The sympathetic branch.
Which branch of the ANS increases after you have eaten?
The parasympathetic.
What does acetylcholine do to the heart?
Act on M2 receptors which decrease heart rate.
Where do the post ganglionic fibres of the parasympathetic ANS sit on the heart?
Epicardial surface or within the walls of the heart.
What does the sympathetic ANS do to the heart?
Innervates the sino atrial and atrial ventricular nodes as well as the myocardium.
What effect does noradrenaline have one heart?
Acts on beta 1 adrenoreceptors so increases the heart rate and force of contraction.
How does the pacemaker of the heart work?
The cells within the sino atrial node steadily depolarise toward the threshold until it meet them then an action potential is fired. This is called the pacemaker potential - turning on of slow Na+ conductance and opening of Ca2+ channels.
What is the action of the sympathetic ANS on the pacemaker potential?
Increases the slope on the graph. This is due to it effecting the beta 1 receptors and increasing cAMP.
Protein kinase causes phosphorylation of Ca2+ channels and and increase in Ca2+ entry during an action potential.
This increases the force of contraction.
What is the action of the parasympathetic ANS on the pacemaker potential?
Decreases the slope on the graph. Uses M2 receptors.
Increases K+ conductance and decreases cAMP.
Which branch of the ANS do most blood vessels receive their innovation from?
The sympathetic. Except specialised tissue eg erectile tissue which receives parasympathetic.
What type of adrenoreceptor does most arteries and veins have?
Alpha 1
Arteries and veins in which 3 extra tissue types have beta 2 adrenoreceptors?
Liver, skeletal and coronary. Adrenaline has a higher affinity for Beta 2 adrenoreceptors.
What is vasomotor tone?
The normal output of a vessel.
What is it called when the output of a vessel increases?
Vasoconstriction.
What is it called when the output of a vessel decreases?
Vasodilation.
How does vasodilation occur?
Activation of the beta 2 adrenoreceptors causes vasodilation by an increase in cAMP that opens the K+ channels so the smooth muscle relaxes.
How does vasoconstriction occur?
Alpha 1 adrenoreceptors are activated.
Increase the concentration of Ca2+ entering the cell so there is contraction of smooth muscle.
What effect does metabolites have on vasomotor tone?
They have a strong vasodilatior effect.
What are baroreceptors?
Nerve endings in the carotid sinus and aortic arch that are sensitive to stretch.
How do baroreceptors work?
When they are stretch due to an increased arterial pressure they feedback to the medulla which adjusts the efferent pathway. (The heart and vessels)
What are the 3 classes of drugs which effect the ANS?
1) Sympathonimetrics
2) Adrenoreceptor antagonists
3) cholinergics
What are the 2 types of Sympathonimetrics?
Alpha adrenoreceptor agonists.
Beta adrenoreceptor agonists.
What are the 2 types of cholinergics?
Muscarinic agonists and antagonists.
What is an example of how muscarinic agonists are used in clinical practice?
Treatment of a glucoma using Pilocapine.
What is an example of how muscularinic antagonists are used in clinical practice?
Tropicqmide is used to dilate the pupils for examination of the eye.
What is a cardiovascular use for Sympathonimetrics?
Adrenaline is used to restore function during a cardiac arrest.
OR
A beta agonist - Dobutamine - used in cardiogenic shock.
What is a clinical use for adrenoreceptor antagonists?
Alpha 1 antagonists eg Prazosin are hypertensive agents. Can be used as an anti hypertensive agent which inhibits the noradrenaline action on vascular smooth muscle causing vasodilation.
Beta adrenoreceptor antagonists eg Propranolol. Can be used to slow heart rate and reduce the force of contraction. Non selective with beta 1/2.
Why is Atenolol sometimes used instead of propranolol?
Because Atenolol is selective for beta 1 which means there is less risk of bronchoconstriction in the patient. - This can be especially dangerous for people with asthma.
